A proper attempt to diagnose the cause of chronic post-surgical pain permits appropriate steering of the clinical management

(1)

I

IAIABC System

Impairment Rating, Ambiguity, IAIABC System

Iatrogenic Causes of Neuropathy

PAOLOMARCHETTINI

Pain Medicine Center, Scientific Institute San Raffaele, Milan, Italy

marchettini.paolo@hsr.it

Synonyms

Post Surgical Nerve Injury; Chronic Postoperative Pain;

Chronic Post-Surgical Neuralgia Definition

Iatros in Greek means physician, the term iatrogenic defines a pathological complication of medical care.

Iatrogenic neuropathyis a nerve injury caused by surgical or pharmacological treatment or by its consequence.

It is estimated that iatrogenic neuropathy is a major cause of chronic pain, although the condition is still unrecognized and poorly managed. The encompassing term “chronic post-surgical pain syndrome” which is commonly used to cluster all these not so rare outcomes of surgery, is unhelpful as it offers little insight into the pathophysiology operating in each case. For the sake of clarity, the use of the widespread terms “failed” and

“syndrome” are not useful when defining post-surgical pain conditions, as they do not determine the etiology of the pain. A proper attempt to diagnose the cause of chronic post-surgical pain permits appropriate steering of the clinical management.

Characteristics

Pain and other abnormal sensory symptoms replicate the typical description of sensory aberration in mono- or poly-neuropathy (Hansson et al. 2001). Iatrogenic neuropathy however, has more psychological complications, because the recognition of nerve injury is often missed or belated. The onset of neuropathic pain can be delayed for days, weeks or, rarely, months. Doctor

and patient may erroneously attribute early onset neuropathic pain to the expected “normal” post-operative pain. The operation was technically successful and there were no infections or other obvious complications. Delayed recognition may also be the consequence of immobilization by postoperative cast, bed rest, re- duced activity or sedation due to anesthetic or analgesic medication. The nerve injury may selectively affect a sensory branch, hampering objective evidence of the lesion. The intensity of the pain is often unrelated to the severity of the nerve damage; indeed partial nerve injury may predispose to neuropathic pain to a greater extent than total injury. When the diagnosis is made, at times many years later, patients are frustrated by delayed treatment and by inadequate and unspecific clinical management (Horowitz 1984). The typical clinical picture of chronic pain, sensory disorder, insomnia and depression is complicated by frustration and disbelief toward physicians and other medical care providers, judged in general to be responsible for the prolonged and unnecessary suffering.

Symptoms

When a patient describes tingling (spontaneous dis- charges in large myelinated fibers), pins and needles (small myelinated fibers), cramps and burning (unmyelinated fibers) in the region of the surgical procedure, iatrogenic nerve injury is high on the list of differential diagnoses. The diagnosis is made based on such typical neuropathic symptoms and on the identification of sensory disorder in the anatomical territory of the injured nerve(s). It is also fundamental to search for a Tinel sign to identify the site of the injury. A condition that may hamper the diagnosis is a partial injury in continuity.

Painful iatrogenic neuropathy often originates from injury confined to a sensory nerve, without evidence of muscle wasting and weakness. At times the nerve injury is rather selective, affecting small fascicular rami and may be hard to detect clinically and electrophysiologi- cally. Command of peripheral nerve sub anatomy helps early recognition. As all neuropathic pains, iatrogenic neuralgia also can be spontaneous and evoked by stimuli to the skin or perhaps just movement. At times even minor stimuli, normally not painful, can evoke a burning and unpleasant tingling sensation or thermal sensations (dysesthesia - allodynia). Stimulus evoked pain is so

(2)

950 Iatrogenic Causes of Neuropathy

distressing that patients report sensory dysfunction beyond the anatomical distribution of hypoesthesia, in territories that are wider than those supplied by the injured nerve. However, sensory dysfunction is usually confined within a territory that surrounds the cutaneous distribution of the affected plexus, root or peripheral nerve. Occasionally, the nerve injury is the consequence of progressive entrapment in the surgical scar. Such entrapment, unlike anatomical entrapment syndromes, is rarely focal, usually being more homogeneously dis- tributed along the scar. In the early phase, ectopic neural activity may exist in the absence of nerve conduction block and neurophysiological signs may remain within normal values for a long time. The clinical equiva- lence is that the positive symptoms of pain, paresthesia and dysesthesia may appear without striking negative phenomena (hypo-anesthesia).

Diagnosis

In clinical practice recognizing a cutaneous nerve injury by the patient’s description of tingling pins and needles and burning is relatively simple. Diagnosing an injury of nerves supplying deep structure is more demanding.

In such cases the pain quality replicates the quality of a deep tissue injury, making the differential diagnosis between neuropathy and connective tissue disease not always so self-evident. Deep neuropathic pain is commonly more widespread and more difficult to localize, it is often referred at a distance from the injury site and might spread along an entire radicular territory. At times entrapment can be related to or aggravated by movement or positioning. If a nerve injury is suspected, a thorough clinical examination including sensory hyperphenom- ena (identification and documentation of allodynia and hyperalgesia) as well as sensory loss and motor function is required. Nerve conduction studies and quantitative sensory testing may be helpful in supporting the clinical diagnosis. When a comparison with a contralat- eral nerve is possible, the sensitivity of such a test is im- proved. The clinical assessment should also take into ac- count that any injury to the sensory component of a motor nerve may result in pain. The motor system should be examined properly through electromyography and motor nerve conduction studies. This comprehensive sen- sorimotor examination allows objective identification of the neurological dysfunction. Careful evaluation means that precise follow-up can be ensured, providing a yard- stick helpful in reassuring the patient that the nerve damage is not worsening and is possibly improving. Such evaluation also provides specific evidence in the event of medico-legal assessment. Assessment of the social and psychological aspects of the disease is also necessary, so that the full picture can be documented.

Epidemiology

Solid data are still much wanted. Cox et al. (1974) found a 27% incidence of neuropathic symptoms in the best-

case scenario after saphenectomy. The majority of the injuries were symptomless. Only 12% of the patients, less than half of those with a clinically identifiable injury, reported subjective sensory abnormalities and only 5% of all operated patients reported pain. The most frequently injured nerves during medical interventions are 1)

brachial plexus; 2) palmar cutaneous branch of the median nerve; 3) infrapatellar cutaneous branch of the saphenous nerve, 4) ilioinguinal, iliohypogastric, gen- itofemoral and femoral nerves, 5) accessory and greater auricular nerves, 6) long thoracic nerve and 7) alveolar nerve. Our observation reiterates the homogeneous lists of Horowitz (1984), Dawson and Krarup (1989) and Sunderland (1991).

The surgical interventions most commonly associated with nerve injury are peripheral anesthetic nerve block, odontoiatric treatment, ENT surgery, cardiovascular surgery, orthopedic surgery and general surgery.

Odontoiatric Treatment

In endodontic surgery, nerve damage may result from direct intrusion of instruments or implants into the mandibular canal or from introducing neurotoxic substances such as paraformaldehyde close to the inferior alveolar nerve.

ENT Surgery

Nasal sinus surgery may damage the maxillary branch of the trigeminal nerve, resulting in persistent pain in the region of the eye (Neuhaus 1990).

Cardiovascular Surgery

Varicose vein striping, particularly of the saphenous vein, may result in nerve injury. After thoracotomy, a sensory disorder, in particular mechanical allodynia indicating a neuropathic component for the pain, has been found in 80 consecutive patients complaining of chronic pain after coronary artery by pass grafting (Eisenberg et al. 2001).

Orthopedic Surgery

Shoulder arthroscopy, as with all arthroscopic tech- niques, is becoming a more frequent cause of iatroge- nesis, although reports vary widely (from 10% to one case out of 439 (Stanish and Peterson 1995).

Carpal tunnel release is a common surgical intervention that can be complicated by a lesion of the median and, more rarely, of the ulnar nerve. The reported incidence of iatrogenic nerve injury varies from five out of eighty three cases to 0.8% in a series of 3035 hands reported in a review of fourteen papers. Almost 10% of patients complaining of complications following endoscopic carpal tunnel release have neuropathic pain (Kelly et al. 1994).

Breast surgery is associated with chronic pain sequels in over 20% of patients (Foley 1990). Harvesting of bone for grafting has been reported amongst the causes of injury to the lateral femoral-cutaneous nerve (Hudson

(3)

I

Iatrogenic Neuropathy 951

et al. 1979). Incision around the knee joint has been associated with lesions of the infrapatellar branch of the saphenous nerve. In 1983, Swanson and co-workers reported a 63.2% incidence of prepatellar neuropathy in eighty-seven patients immediately after open meniscectomy, while Sherman and co-workers noted only a 0.6% incidence of reported symptoms following 2,640 arthroscopic procedures on the knee (Swanson 1983, Sherman et al. 1986). In 1995, Mochida and Kikuchi reported a 22.2% incidence of sensory disturbances in sixty-eight consecutive patients operated on between 1990 and 1991 (Mochida and Kikuchi 1995). Limb amputation is also frequently followed by chronic pain (the highest frequency reported is as high as 80% of the amputees).

General Surgery

Lymph node biopsy in the neck is sometimes associated with injury to the accessory nerve and cutaneous nerves in the neck (Murphy 1983). Ilioinguinal nerve lesion is an important complication following inguinal hernioplasty (Heise and Starling 1998). Anterior hernioplasty, which requires the dissection of spermatic cord and sensory nerves, is a more common cause of this injury.

Laparoscopic repair of the hernia is increasing simulta- neously with the injuries to neural structures coursing through the groin. The femoral branches of the gen- itofemoral nerve and the lateral cutaneous nerve of the thigh, not visible during laparoscopic inguinal hernia repair, are more vulnerable. Abdominal rectopexy has been associated with femoral nerve injury in six patients out of a series of twenty-four patients, twenty-one of whom were operated on for rectal prolapse and three for recto-rectal intussusception (Infantino et al. 1994).

Therapy

Treatment of painful iatrogenic neuropathy requires all means used in the management of any other neuropathic pain (Senegor 1991, Sindrup and Jensen 1999). In this medically provoked condition, it is even more fundamental to care for the psychological co-morbidities.

These should be prevented by early recognition of the neuropathic symptoms and the identification of the injured nerve. Early recognition, besides improving pain management, avoiding psychological overlay and possibly preventing chronification, favors the reestab- lishment of a trustful patient doctor relationship.

References

1. Cox SJ, Wellwood JM, Martin A (1974) Saphenous nerve injury caused by stripping of the long saphenous vein. Br Med J 1:415–417

2. Dawson DM, Krarup C (1989) Perioperative nerve lesions. Arch Neurol 46:1355–1360

3. Eisenberg E, Pultorak Y, Pud D et al. (2001). Prevalence and characteristics of post coronary artery bypass graft surgery pain (PCP). Pain 92:11–17

4. Foley KM (1990) Brachial plexopathy in patients with breast cancer. In: Harris JR, Hellman S, Henderson IC et al. (eds) Breast Diseases, 2nd edn. Lippincott JB, Philadelphia, pp 722–729

5. Hansson PT, Lacerenza M, Marchettini P (2001) Aspects of clinical and experimental neuropathic pain: the clinical perspective.

In: Hansson PT, Fields HL et al. (eds) Neuropathic Pain: Patho- physiology and Treatment. Progress in Pain Research and Man- agement. IASP Press, Seattle, pp 1–18

6. Heise CP, Starling JR (1998) Mesh inguinodynia: a new clinical syndrome after inguinal herniorrhaphy? J Am Coll Surg 87:514–518

7. Horowitz SH (1984) Iatrogenic causalgia. Classification, clinical findings, and legal ramifications. Arch Neurol 41:821–824 8. Hudson AR, Hunter GA, Waddell JP (1979) Iatrogenic femoral

nerve injuries. Can J Surg 22:62–66

9. Infantino A, Fardin P, Pirone E et al. (1994) Femoral nerve damage after abdominal rectopexy. Int J Colorectal Dis 9:32–4 10. Kelly CP, Pulisetti D, Jamieson AM (1994) Early experience with

endoscopic carpal tunnel release. J Hand Surg (Br) 19:18–21 11. Mochida H, Kikuchi S (1995) Injury to infrapatellar branch of

saphenous nerve in arthroscopic knee surgery. Clin Orthop Relat Res 320:88–94

12. Murphy TM (1983) Complications of diagnostic and therapeutic nerve blocks. In: Orkin FK, Cooperman LH (eds) Complications in anaesthesiology. Lippincott, Philadelphia

13. Neuhaus RW (1990) Orbital complications secondary to endoscopic sinus surgery. Ophthalmology 97:1512–1518

14. Senegor M (1991) Iatrogenic saphenous neuralgia: successful therapy with neuroma resection. Neurosurgery 28:295–298 15. Sherman OH, Fox JM, Snyder SJ et al. (1986) Arthroscopy-"no-

problem surgery” An analysis of complications in two thousand six hundred and forty cases. JBJS 68:256–265

16. Sindrup SH, Jensen TS (1999) Efficacy of pharmacological treat- ments of neuropathic pain: an update and effect related to mech- anism of drug action. Pain 83:389–400

17. Stanish WD, Peterson DC (1995) Shoulder arthroscopy and nerve injury: pitfalls and prevention. Arthroscopy 11:458–466 18. Sunderland S (1991) Miscellaneous causes of nerve injury. In:

Sunderland S (ed) Nerve injuries and their repair. A critical ap- praisal. Churchill- Livingstone, Edinburgh, pp 197–199 19. Swanson AJ (1983) The incidence of prepatellar neuropa-

thy following medial meniscectomy. Clin Orthop Relat Res 181:151–153

Iatrogenic Effect/Response

Definition

Iatrogenic effects/responses are outcomes inadvertently induced by a physician or surgeon or by medical treatment or diagnostic procedures.

Acute Pain Management in Infants

Cancer Pain, Assessment in Children

Iatrogenic Neuropathy

Definition

Iatrogenic neuropathy is a nerve injury caused by surgical or pharmacological treatment, or by its consequence.

(4)

952 IB4-Binding Neurons

IB4-Binding Neurons

IB4-Positive Neurons, Role in Inflammatory Pain

CHERYLL. STUCKY

Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI, USA

cstucky@mcw.edu

Synonyms

IB4-Binding Neurons; GDNF-Dependent Neurons;

IB4-Positive Nociceptors

Definition

An IB4-positive neuron is a sensory neuron whose cell body lies in the dorsal root or trigeminal ganglia and whose membrane expresses surface carbohydrates (α- D galactose groups of glycol conjugates) that bind the plant lectin isolectin B4 (IB4) fromGriffonia simplici- folia I. IB4-positive neurons have small size cell bodies and primarily give rise to unmyelinated fibers, many of which are nociceptive.

Characteristics

IB4-positive neurons comprise one of two broad classes of small diameter, C-fiber sensory neurons. The other class (IB4 negative) typically expresses neuropeptides such as substance P and calcitonin gene related peptide (CGRP) and expresses trkA receptorsfor nerve growth factor(NGF). IB4-positive neurons express receptors forglial cell line-derivedneurotrophic factor

IB4-Positive Neurons, Role in Inflammatory Pain, Figure 1 Schematic of cross- section of the lumbar spinal cord and innervation by the general subclasses of primary afferent neurons.

(GDNF) and depend on GDNF for survival after birth (Bennett et al. 1998). IB4 positive neurons selectively express the P2X3 Receptor for ATP. IB4-positive neurons are relatively poor in expression of neuropeptides or trkA receptors (Silverman and Kruger 1990;

Averill et al. 1995; Molliver et al. 1995), but some studies show overlap between IB4 binding and neuropeptide or trkA expression (Wang et al. 1994; Kashiba et al.

2001). The central terminals of IB4-positive neurons terminate predominantly in the inner lamina II of the superficial dorsal horn of the spinal cord (Gerke and Plenderleith 2004), whereas IB4-negaitve neurons terminate mainly in lamina I and outer lamina II (Fig. 1).

The neurochemical differences between IB4 positive and negative neurons suggest that the two classes of small diameter neurons may have different functional properties in conveying nociceptive information. Com- pared to IB4 negative neurons, IB4 positive neurons isolated from uninjured mice or rats have longer duration action potentials and higher densities oftetrodotoxin (TTX) resistant sodium channelcurrents (Stucky and Lewin 1999), higher densities of N-type Ca²⁺channel currents (Wu and Pan 2004) and higher densities of voltage gated K⁺(Kv) channel currents (Vydyanathan et al. 2005). Furthermore, IB4 positive neurons from uninjured mice are significantlyless responsive to noxious chemical stimuli, including capsaicin and protons, than IB4 negative neurons (Dirajlal et al. 2003).

Several authors have hypothesized that IB4 negative, but not IB4 positive, neurons contribute to inflammatory pain (Mantyh and Hunt 1998; Snider and McMahon 1998). To address this hypothesis, a recent study investigated whether peripheral inflammationin vivo alters the response properties of isolated IB4 positive or IB4 negative neurons to the noxious stimulus capsaicin, which activates the transient receptor potential vanilloid 1 (TRPV1) receptor ( TRPV1 receptor) (Breese et al. 2005). TRPV1 function was investigated because

(5)

I

IB4-Positive Neurons, Role in Inflammatory Pain 953

IB4-Positive Neurons, Role in Inflammatory Pain, Figure 2 Inflammation sensitizes IB4 positive neurons to capsaicin. (a) Examples of whole cell voltage clamp recordings from an IB4 positive and an IB4 negative small diameter neuron (≤ 26 μ m) that responded to 1 μ M capsaicin. (b) Percentage of IB4 positive and IB4 negative neurons from the L4/L5 DRG of control or CFA-injected mice that responded to a 10 s exposure to 1μ M capsaicin.

Capsaicin-evoked currents in all cells tested were> 40 pA.*** indicates that significantly more IB4 positive neurons from inflamed mice responded to capsaicin compared to the control IB4 positive group (P< 0.0001; Fisher’s Exact test). (c) Percentage of IB4 positive and IB4 negative small diameter neurons isolated from the L4/L5 DRG from control or CFA-injected mice that responded to 100 nM capsaicin.* indicates that significantly more IB4 positive neurons from inflamed mice responded to capsaicin compared to control IB4 positive neurons (P< 0.05; Fisher’s Exact test). The percentage of IB4 negative neurons that responded to 100 nM capsaicin was unaltered by inflammation. (Modified from Breese et al. 2005).

TRPV1 is a key heat transducer on nociceptors and me- diates the heat hyperalgesia that accompanies peripheral inflammation (Caterina et al. 2000; Davis et al. 2000).

Peripheral inflammation was induced by injection of

complete Freund’s adjuvant(CFA) in the hind paw of mice. Two days later, the lumbar 4–5 ganglia, which contain the cell bodies of neurons that project to the hind paw were isolated and dissociated and whole cell patch clamp recordings were performed on small diameter neurons. Fig. 2 shows that the proportion of IB4 positive neurons that respond to capsaicin with an inward current is markedly increased (3-fold) after inflammation, whereas IB4 negative neurons are unaltered. The increase in capsaicin responsiveness in IB4 positive neurons is due to increased TRPV1 function because IB4 positive neurons fromTRPV1-Null Micewith CFA inflammation are unresponsive to capsaicin. Similarly, inflammation increases the proportion of IB4 positive

IB4-Positive Neurons, Role in Inflammatory Pain, Table 1 TRPV1- immunoreactivity in IB4 positive and IB4 negative small diameter neurons from control and CFA-injected mice

TRPV¹⁻ir ( % ) Control ( % ) Inflamed ( % )

% total neurons 10.7± 4.0 25.0± 3.0 *

% of IB4 positive neurons 4.5± 2.1 15.5± 3.6 †

% of IB4 negative neurons 20.9± 12.2 34.7± 8.6 m) L4/L5 DRG neurons co-stained for IB4 and TRPV1. * indicates that thepercentage of neurons that are TRPV1-mmunoreactive(TRPV1-ir) was increased in CFA-injected mice compared tocontrol mice (P< 0.05; two- tailed unpaired t -test). † indicates thatthe percentage of IB4 positive neu- rons that are TRPV1-ir wasincreased in CFA-injected mice compared to con- trol mice (P< 0.05; two-tailed unpairedt-test). The percentage of TRPV1- ir IB4 negativeneurons was not significantly altered in CFA-injected mice compared to controlmice (P> 0.3; two-tailed unpairedt-test). n = 5 con- trol mice (1201total neurons analyzed for TRPV1 and IB4 staining); n = 12 CFA-injected mice (1232 total neurons analyzed for TRPV1and IB4 staining) (Breese et al. 2005).

neurons, but not IB4 negative neurons, that respond to protons (pH 5.0) in a TRPV1-dependent manner (not shown). In parallel, CFA-induced inflammation increases by 3-fold the percentage of IB4-positive neurons that express TRPV1-immunoreactivity, but has no effect on IB4 negative neurons (Fig. 3 and Table 1).

Since the IB4 positive small diameter neurons are selectively increased in TRPV1 function and expression during peripheral inflammation, they may play an important role in inflammatory pain. Natural stimuli for TRPV1 during inflammation may be noxious heat or endogenous TRPV1 ligands including protons,N- arachidonoyl-dopamine, anandamide or eicosanoids such as leukotriene B4, 12-(S)-HPETE or 15-(S)- HPETE molecules. An increase in the number of IB4 positive neurons that respond to TRPV1 stimuli including heat or endogenous TRPV1 inflammatory ligands could increase, by spatial summation, the amount of nociceptive information transmitted to the dorsal horn of the spinal cord and ultimately contribute to inflammatory pain and hyperalgesia. The IB4-positive neurons’ capacity to become sensitized highlights them as a putative target for novel therapies for inflammatory pain.

References

1. Averill S, McMahon SB, Clary DO et al. (1995) Immuno- cytochemical localization of trkA receptors in chemically identified subgroups of adult rat sensory neurons. Eur J Neu- rosci 7:1484–1494

2. Bennett DL, Michael GJ, Ramachandran N et al. (1998) A distinct subgroup of small DRG cells express GDNF receptor com- ponents and GDNF is protective for these neurons after nerve injury. J Neurosci 18:3059–3072

3. Breese NM, George AC, Pauers LE et al. (2005) Peripheral inflammation selectively increases TRPV1 function in IB4-positive sensory neurons from adult mouse. Pain 115:37–49

4. Caterina MJ, Leffler A, Malmberg AB et al. (2000) Impaired nociception and pain sensation in mice lacking the capsaicin receptor. Science 288:306–313

(6)

954 IB4-Positive Neurons, Role in Inflammatory Pain

IB4-Positive Neurons, Role in Inflammatory Pain, Figure 3 Inflammation increases TRPV1-immunoreactivity in IB4-positive neurons. Confocal images of acutely isolated DRG neurons from control (a) and CFA-injected (b) wild-type mice that were co-stained with IB4 and a TRPV1 antibody. Lumbar 4/5 DRG neurons were isolated from control, non-injected mice or mice 22 days after CFA injection and fixed 6-9 h later for staining. Merged confocal images show that few IB4-positive neurons from control mice are TRPV1-immunoreactive, but after CFA-induced peripheral inflammation, more IB4-positive neurons are immunoreactive for TRPV1. Although neurons from control and inflamed mice were fixed at thee same time after isolation, neurons from CFA-injected mice typically exhibited more processes, less round somata and more clustering than controls.

5. Davis JB, Gray J, Gunthrope MJ et al. (2000) Vanilloid receptor-1 is essential for inflammatory thermal hyperalgesia.

Nature 405:183–187

6. Dirajlal S, Pauers LE, Stucky CL (2003) Differential response properties of IB(4)-positive and -negative unmyelinated sensory neurons to protons and capsaicin. J Neurophysiol 69:1071–1081

7. Gerke MB, Plenderleith MB (2004) Ultrastructural analysis of the central terminals of primary sensory neurones labeled by trans-

ganglionic transport of Bandeiraea simplicifolia I-isolectin B4.

Neuroscience 127:165–175

8. Kashiba H, Uchida Y, Senba E (2001) Difference in binding by isolectin B4 to trkA and c-ret mRNA-expressing neurons in rat sensory ganglia. Brain Res Mol Brain Res 95:18–26 9. Mantyh PW, Hunt SP (1998) Hot peppers and pain. Neu-

ron 21:644–645

10. Molliver DC, Radeke MJ, Feinstein SC et al. (1995) Presence or absence of TrkA protein distinguishes subsets of small sensory

(7)

I

IDET 955

neurons with unique cytochemical characteristics and dorsal horn projections. J Comp Neurol 361:404–416

11. Silverman JD, Kruger L (1990) Selective neuronal glycocon- jugate expression in sensory and autonomic ganglia: relation of lectin reactivity to peptide and enzyme markers. J Neu- rosci 23:789–801

12. Snider WD, McMahon SB (1998) Tackling pain at the source:

new ideas about nociceptors. Neuron 20:629–632

13. Stucky CL, Lewin GR (1999) Isolectin B(4)-positive and -negative nociceptors are functionally distinct. J Neurosci 19:6497–6505

14. Vydyanathan A, Wu ZZ Chen SR et al. (2005) A-type voltage- gated K+ currents influence firing properties of isolectin B4- positive but not isolectin B4-negative primary sensory neurons.

J Neurophysiol 93:3401–3409

15. Wang H, Rivero-Melian C, Robertson G et al. (1994) Trans- ganglionic transport and binding of the isolectin B4 from Griffonia simplicifolia I in rat primary sensory neurons. Neu- roscience 62:539–551

16. Wu ZZ, Pan HL (2004) High voltage-activated Ca(²⁺) channel currents in isolectin B(4)-positive and -negative small dorsal root ganglion neurons of rats. Neurosci Lett 368:96–101

IB4-Positive Nociceptors

IB4-Positive Neurons, Role in Inflammatory Pain

IBS

Descending Modulation of Visceral Pain

Irritable Bowel Syndrome

Visceral Pain Model, Irritable Bowel Syndrome Model

IC₅₀Value

Definition

IC50 Value is the concentration where 50% of the inhibitory effect of a drug is reached.

NSAIDs, COX-Independent Actions

Ice-Pick Pain

Definition

This describes a sharp jabbing pain in contrast to a per- sisting ache.

Primary Stabbing Headache

Ice-Water Bucket Test

Definition

A test involving immersing an extremity into a bucket filled with ice and water, usually resulting in a temperature of 4 degrees Celsius. The test can be used as a test of pain sensitivity (e.g. by measuring how long the extremity is left immersed before pain becomes intolerable) or as a defined conditioning stimulus for testing the body’s inhibitory responses to pain or nociceptive input. If the latter is intended, the extremity is left in the bucket for a defined length of time (or until a defined temperature is reached), with quantitative sensory testing (or other for- mal sensory testing) being performed before and after the test to quantitate the inhibitory response.

Quantitative Sensory Testing

ICF

Definition

International Classification of Functioning, Disability and Health. It was developed by the World Health Orga- nization. The ICF has addressed many of the criticisms of prior conceptual frameworks, and has been developed in a worldwide comprehensive consensus process over the few last years.

Disability and Impairment Definitions

ICSI

Synonym

O’Leary-Sant Interstitial Cystitis Symptom Index

Definition

ICSI stands for O’Leary-Sant Interstitial Cystitis Symp- tom Index, which is utilized for quantifying the degree of symptoms associated with interstitial cystitis.

Interstitial Cystitis and Chronic Pelvic Pain

IDET

Synonym

Intra Discal Electrothermal Therapy

Definition

IDET stands for Intra Discal Electrothermal Ther- apy – this technique is also called annuloplasty, and

(8)

956 Idiopathic

involves treatment of posterior annulus with heat from a thermal resistive coil in an attempt to repair, denervate and stabilize an annular tear.

Discogenic Back Pain

Intradiscal Electrothermal Therapy

Spinal Fusion for Chronic Back Pain

Idiopathic

Definition

If a condition or disease is of unknown cause, it is described as idiopathic.

Diabetic Neuropathies

Idiopathic Ataxic Neuropathy

Ganglionopathies

Idiopathic Cramps

Definition

This type of cramp is the main symptom of a disease about which little is known, the cause of the cramp being obscure or speculative. Idiopathic cramps can be either sporadic or inherited, and are usually not associated with any cognitive, pyramidal, cerebellar, or sensory abnormalities.

Muscular Cramps

Idiopathic Headache

Headache, Episodic Tension Type

Idiopathic Myalgia

Myalgia

Idiopathic Orofacial Pain

Atypical Facial Pain, Etiology, Pathogenesis and Management

Idiopathic Stabbing Headache

Primary Stabbing Headache

Idiopathic Vulvar Pain

Vulvodynia

IEGs

Immediate Early Genes

iGluRs

Ionotropic Glutamate Receptors

Ignition Hypothesis

Definition

Hypothesis, proposed by Rappaport and Devor (1994), which attempts to explain paroxysmal pain in trigeminal neuralgia in terms of sustained afterdischarge and cross excitation, amplified by positive feedback among neighboring neurons in the trigeminal root and/or ganglion.

Pain Paroxysms

Tic and Cranial Neuralgias

IL–1beta

Definition

IL-1beta is a cytokine with many properties similar to TNF. At higher endocrine concentrations, it is associated with fever and formation of acute-phase plasma proteins in the liver.

Cytokines as Targets in the Treatment of Neuropathic Pain

IL-4

Definition

Interleukin-4 is an anti-inflammatory cytokine that has also been shown to have analgesic properties.

(9)

I

Immune Cell Recruitment 957

IL-6

Definition

IL-6 is a cytokine with mostly proinflammatory and al- gesic actions. It is a member of the IL-6 cytokine family that includes leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF).

IL-10

Definition

Interleukin-10 is an anti-inflammatory cytokine that has also been shown to have analgesic properties.

Ilium

Definition

The Ilium is the upper portion of the hipbone.

Sacroiliac Joint Pain

Illness Behaviour

Interpersonal Pain Behaviour

Illusory Cramp

Definition

Illusory cramp is a phenomenon in which the sensation of cramping is experienced, but little or no contraction of the muscle occurs.

Muscular Cramps

Imagery

Definition

Representations in the mind of visual, auditory, tactile, olfactory, gustatory or kinesthetic experiences. The subjective reality of these experiences may vary between and within individuals. Guided, directed or elicited imagery can be a potent means of changing subjective experiences of pain.

Therapy of Pain, Hypnosis

IME

Independent Medical Examinations

Imitation Learning

Modeling, Social Learning in Pain

Immediate Early Genes

Synonym IEGs Definition

Immediate early genes (IEGs) are genes that are rapidly induced in the absence of de novo protein synthesis.

The best characterized immediate early genes are c-jun and c-fos; both genes encode transcription factors that bind to specific regulatory sequences and activate expression of responsive genes. c-jun has a leucine zipper motif, which forms a heterodimer with a variety of proteins including c-fos. The jun-fos protein complex, also known as the activator complex (AP)-1, binds to a number of cellular promoters through a common element (5’-TGACTCA-3’). IEGs are distinct from

“late response” genes, which can only be activated later following the synthesis of early response gene products.

IEGs have therefore been called the “gateway to the genomic response“.

Amygdala, Pain Processing and Behavior in Animals

NGF, Regulation during Inflammation

Immortalization

Definition

Immortalization is to confer the property of continuous division by the addition or upregulation of a gene, that when expressed in the cell, stimulates the cell to contin- uously divide until removed or downregulated.

Cell Therapy in the Treatment of Central Pain

Immune Cell Recruitment

Definition

Inflammation induces immune cell migration from the circulation in multiple steps, including rolling, adhesion, and transmigration of immune cells through the vessel wall.

Opioids and Inflammatory Pain

(10)

958 Immune Cells

Immune Cells

Definition

B- and T-lymphocytes, macrophages and monocytes are immune cells patrolling through the body. They can mi- grate to areas with inflammation (chemotaxis).

Opioid Modulation of Nociceptive Afferents in vivo

Immunocompetent Cells

Definition

Immunocompetent cells are able to respond to bacterial and viral stimuli. These cells respond by releasing clas- sical immune mediators including proinflammatory cytokines. Within the CNS, these cells include astrocytes and microglia. Activation of these cells with immuno- genic substances induces exaggerated pain.

Cord Glial Activation

Immunocytochemistry

Definition

Immunocytochemistry is a method for demonstrating the localization of compounds in tissues, based on the use of antibodies.

Immunocytochemistry of Nociceptors

Opioid Receptors at Postsynaptic Sites

CHERYLL. STUCKY

Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI, USA

cstucky@mcw.edu

Synonyms

Immunohistochemistry; Immunoreactivity; Immunos- taining; Neurochemistry; Neurochemical Markers;

Nociceptors, Immunocytochemistry Definition

The study of molecules or proteins (antigens) found in the cytoplasm or membrane of nociceptors by using immunologic staining methods, such as the use of fluorescent antibodies or enzymes (e.g. horseradish peroxidase). The immunocytochemistry procedure is usually performed on sections of tissue that has been fixed by a cross-linking fixative like paraformaldehyde or glutaraldehyde. Typical tissues include the dorsal

root or trigeminal ganglion, peripheral nerve or target tissue such as skin. Most of these immunocytochemical markers label not only the cell bodies but also the axons and terminals of the sensory neurons.

Characteristics

Nociceptive sensory neurons express a large variety of molecules that are involved in neuronal communication and many of these molecules are present in high enough concentrations to be detected by immunocytochemical methods. For example, nociceptors contain neurotrans- mitters and neuropeptides which, when released from central terminals act on spinal cord neurons or when released from peripheral terminals act on other cells in the skin or target tissues. Furthermore, nociceptors express ion channels and receptors in their plasma membrane that allow them to respond to external stimuli (heat, cold, mechanical force) or internal stimuli such as molecules released by other cell types. The goal of this essay is to highlight examples of the major immunocytochemical markers that are most frequently used to characterize subpopulations of nociceptors within thedorsal root ganglion(DRG) or trigeminal ganglion. However, because DRG and trigeminal neurons are exceptionally heterogeneous with respect to their expression of peptides, enzymes and receptors, there are many molecules and subpopulations of neurons that are not described here.

Peptidergic Population: CGRP and Substance P

The most extensively characterized neuropeptides in nociceptive sensory neurons arecalcitonin gene related peptide(CGRP) andsubstance P. The CGRP- and substance P-expressing population of small diameter neurons is frequently called the “peptidergic”

population of small diameter neurons because both of these neuropeptides are found in many small diameter neurons that stain darkly with basic aniline dyes and are called “small dark cells.” Small dark cells can be distinguished from large light cells, which stain clear or lightly, because they contain many neurofilaments that do not stain with the basic dyes.

Calcitonin Gene-related Peptide

CGRP is expressed by more sensory neurons than other peptides and estimates range from 20–80% of DRG or trigeminal ganglion neurons expressing CGRP. The wide range among studies is due to differences between species, the location along the cervical to sacral neuraxis, the target tissue innervated and whether or not colchicine, which blocks microtubule transport of neuropeptides, was used. Most studies agree that 35–50% of all rat lumbar DRG neurons express CGRP.

Within the spinal cord, CGRP is localized exclusively in primary afferent neurons. Most CGRP-expressing sensory neurons are small or medium size in diameter (many are nociceptors), but a few are large diameter.

(11)

I

Immunocytochemistry of Nociceptors 959

This is consistent with the finding that the afferent fibers of CGRP-positive neurons are primarily unmyelinated C fibers and thinly myelinated Aδ fibers and a few are large myelinated Aβ fibers (McCarthy and Lawson 1990).

Substance P

Substance P (SP) is expressed in approximately 20%

of DRG neurons and most of these are small diameter neurons, although a few are medium diameter. Con- sistent with this, individually identified SP-expressing DRG neurons have either C fiber or Aδ fiber axons and exhibit nociceptive response properties (Lawson et al.

1997). Substance P is highly colocalized with CGRP in that nearly all SP-expressing DRG neurons also contain CGRP, although only half of the CGRP-expressing neurons also contain SP.

Other Characteristics

The peptidergic population of small dark neurons over- laps extensively with expression of trkA, the high affinity receptor for the neurotrophinnerve growth factor (NGF) and depends on NGF for survival during development (Averill et al. 1995). Because good antibodies are available for the trkA receptor, immunocytochemistry for trkA is frequently used as an alternative marker for the peptidergic population of small dark neurons. The central terminals of the peptidergic/trkA neurons are concentrated in lamina I and II

outerof the superficial dorsal horn as well as in lamina V and X of the spinal cord.

CGRP-positive and SP-positive neurons innervate all types of peripheral target tissue, including skin, muscle, joint, bone and visceral organs. It is important to note that the expression pattern and levels of CGRP and SP in DRG neurons change with injury. Both CGRP and SP increase following persistent peripheral inflammation and conversely, they decrease following peripheral nerve lesion (Donnerer et al. 1992; Villar et al. 1991).

This caveat must be carefully considered when using these markers to label and follow subpopulations of neurons in models of injury.

Other neuropeptides found in (typically smaller) subpopulations of mammalian DRG neurons that can be localized via antibody staining include somatostatin, vasoactive intestinal peptide, galanin, vasopressin, bombesin, dynorphin, enkephalin, neuropeptide Y, cholecystokinin and endothelin-1. Their distribution and characteristics will not be discussed in detail here.

Non-Peptidergic or “Peptide Poor” Population:

Isolectin B4 and FRAP

The population of small dark C fiber neurons that is poor in expression of the neuropeptides CGRP or SP is typically characterized by labeling with the plant lectin, isolectin B4 (IB4). Isolectin B4 binds to surface carbohydrates, specifically the Alpha(α)-D Galactose

groups of glycol conjugates (Silverman and Kruger 1990). The IB4 binding technique is most frequently used today because it is very adaptable, easy to perform, and IB4 conjugated directly to fluorescein (IB4-FITC) or other fluorescent markers can be used to label live neurons within minutes after performing physiological experiments (Stucky and Lewin 1999). However, the

“peptide poor” population can also be labeled by immunoreactivity to the antibody LA4, which recognizes the α-galactose oligosaccharides (Dodd and Jessell 1985) or by the presence of the fluoride resistant acid phosphatase (FRAP) enzyme, an extra-lysosomal acid phosphatase that is resistant to fluoride ions (Silverman and Kruger 1988). The function of theα-D galactose groups is not clear, but they have been hypothesized to play a role in the cell-cell interactions during the development of connections of primary afferent neurons to the dorsal horn of the spinal cord (Dodd and Jessell 1985). The function of FRAP is not known.

Other Characteristics

The IB4 positive/FRAP positive population of small diameter neurons also expresses receptors forglial cell- line derived neurotrophic factor(GDNF) and depends on GDNF for survival during postnatal development (Molliver et al. 1997; Bennett et al. 1998). Receptors for GDNF include the ligand binding domainGFRα1 or GFRα2and the signal transducing, tyrosine kinase domain, RET. IB4 positive neurons primarily terminate in lamina IIinnerof the superficial dorsal horn of the spinal cord, a region also known as the substantia gelatinosa.

Although a number of investigations have reported a clear separation between the peptidergic/trkA and the non-peptidergic/IB4 binding populations, other reports indicate that CGRP/SP/trkA and IB4/FRAP staining overlap extensively (Wang et al. 1994; Kashiba et al.

2001). The diverse findings may be due to differences in methods used or sensitivity of detection of the labels. It is likely that there is at least a subpopulation of neurons that expresses neuropeptides and binds IB4.

Importantly, IB4 binding decreases substantially following nerve injury (Bennett et al. 1998) and therefore caution must be exercised when using this marker to label subpopulations of neurons in animal models of injury.

Neurofilament Markers: Antibodies RT97 and N52

The antibody clones RT97 and N52 both recognize the high molecular weight (200 kD)neurofilament protein NF200,which is found in sensory neurons that have myelinated axons. Both RT97 and N52 antibody labeling have been used to identify the large light population of DRG neurons. One difference between the two antibodies is that RT97 recognizes only the phosphorylated form of the 200 kD neurofilament protein whereas N52 recognizes both the phosphorylated and

(12)

960 Immunocytochemistry of Nociceptors

non-phosphorylated forms of the protein. Thus, there may be some differences in the populations of neurons labeled by these two markers. An advantage of RT97 is that a cell-by-cell correlation between RT97 staining and conduction velocities has been made for rat and all A fiber (Aδ and Aβ) DRG neurons were found to be RT97-positive whereas all C fiber neurons were RT97-negative (Lawson and Waddell 1991). No such correlation between N52 and conduction velocity has yet been made.

There is almost no overlap between RT97 and IB4 staining or between N52 and IB4 staining, indicating that RT97/N52 and IB4 label distinct subpopulations of large light and small dark neurons, respectively.

There is, however, significant overlap between RT97 and CGRP as approximately 30% of RT97-positive neurons contain CGRP and these are medium/large size neurons (McCarthy and Lawson 1990).

Ion Channels: TRPV1 and P2X3

Subpopulations of nociceptors can also be identified by antibodies that recognize specialized transduction molecules on the plasma membrane. Examples of these include receptors for noxious heat (TRPV1 receptor) and for ATP (P2X3receptor).

Transient Receptor Potential Vanilloid 1 (TRPV1) Receptor

The TRPV1 receptor/ion channel is the receptor for capsaicin, the potent algogen found in “hot” chili peppers (Caterina et al. 1997). Formerly known as VR1, TRPV1 is a member of the transient receptor potential family of ion channelsand when activated, allows calcium and sodium to flow into the neuron, resulting in depolarization. Besides capsaicin, TRPV1 also responds to moderately noxious heat (> 43˚C), acid (~pH 5.0) and a number of other endogenous ligands that may be present during inflammation or injury, including N-arachidonoyl-dopamine, anandamide or

eicosanoidssuch as leukotriene B4, 12-(S)-HPETE or 15-(S)-HPETE molecules. Good antibodies to TRPV1 exist and TRPV1 immunoreactivity is found on many small diameter and some medium diameter sensory neurons (Caterina et al. 1997). Because capsaicin responsiveness is often used as a functional marker for nociceptors, TRPV1-immunoreactivity is frequently used as a neurochemical marker for nociceptors. Many TRPV1-immunoreactive neurons contain the neuropeptides CGRP or SP, whereas others bind IB4 (Tominaga et al. 1998). As is the case with neuropeptide immunoreactivity and IB4 binding, TRPV1 expression is also not stable after injury. The mRNA and protein for TRPV1 decreases in directly injured DRGs afteraxotomyor

Spinal Nerve Ligation Model. Conversely, TRPV1 increases in adjacent DRGs after spinal nerve ligation and is reported to increase following peripheral inflammation (Hudson et al. 2001).

P2X₃Receptor for ATP

Extracellular adenosine triphosphate (ATP) has been implicated in nociceptive signaling in normal and pathological pain conditions and ATP directly excites nociceptors. P2X3receptors are multimeric ion channels gated by ATP. They exist on native DRG neurons as either P2X3homomers or as a heteromeric combina- tion with the P2X2receptor (P2X2/3). Good antibodies against the P2X3receptor are available and studies doc- ument that P2X3receptors are selectively expressed on small diameter DRG neurons. Under uninjured conditions, P2X3receptors are almost exclusively localized to the IB4-binding population and only a few P2X3- positive neurons contain neuropeptides (Bradbury et al., 1998). Consistent with the pattern for IB4 binding neurons, the central terminals of P2X3-expressing neurons project primarily to the lamina IIinner of the superficial dorsal horn. The expression of P2X3recep- tors decreases following nerve injury and this decrease can be reversed by in vivo administration of GDNF (Bradbury et al. 1998).

References

1. Averill S, McMahon SB, Clary DO et al. (1995) Immuno- cytochemical localization of trkA receptors in chemically identified subgroups of adult rat sensory neurons. Eur J Neu- rosci 7:1484–1494

2. Bennett DL, Michael GJ, Ramachandran N et al. 1998) A distinct subgroup of small DRG cells express GDNF receptor compo- nents and GDNF is protective for these neurons after nerve injury.

J Neurosci 18:3059–3072

3. Bradbury EJ, Burnstock G, McMahon SB (1998) The expression of P2X3 purinoreceptors in sensory neurons: effects of axotomy and glial-derived neurotrophic factor. Mol Cell Neurosci 12:256–268

4. Caterina MJ, Schumacher MA, Tominaga M, Rosen TA, Levine JD, Julius D (1997) The capsaicin receptor: a heat-activated ion channel in the pain pathway. Nature 389:816–824

5. Dodd J, Jessell TM (1985) Lactoseries carbohydrates specify subsets of dorsal root ganglion neurons projecting to the superficial dorsal horn of rat spinal cord. J Neurosci 5:3278–3294 6. Donnerer J, Schuligoi R, Stein C (1992) Increased content and

transport of substance P and calcitonin gene-related peptide in sensory nerves innervating inflamed tissue: evidence for a regulatory function of nerve growth factor in vivo. Neuro- science 49:693–698

7. Hudson LJ, Bevan S, Wotherspoon G et al. (2001) VR1 protein expression increases in undamaged DRG neurons after partial nerve injury. Eur J Neurosci 13:2105–2114

8. Kashiba H, Uchida Y, Senba E (2001) Difference in binding by isolectin B4 to trkA and c-ret mRNA-expressing neurons in rat sensory ganglia. Brain Res Mol Brain Res 95:18–26 9. Lawson SN, Waddell PJ (1991) Soma neurofilament immunore-

activity is related to cell size and fibre conduction velocity in rat primary sensory neurons. J Physiol 435:41–63

10. Lawson SN, Crepps BA, Perl ER (1997) Relationship of substance P to afferent characteristics of dorsal root ganglion neurones in guinea-pig. J Physiol 505:177–191

11. McCarthy PW, Lawson SN (1990) Cell type and conduction velocity of rat primary sensory neurons with calcitonin gene-related peptide-like immunoreactivity.34:623–632

12. Molliver DC, Wright DE, Leitner MJ et al. (1997) IB4-binding DRG neurons switch from NGF to GDNF dependence in early postnatal life. Neuron 19:849–861

(13)

I

Impact of Familial Factors on Children’s Chronic Pain 961

13. Silverman JD, Kruger L (1988) Lectin and neuropeptide labeling of separate populations of dorsal root ganglion neurons and associated “nociceptor” thin axons in rat testis and cornea whole- mount preparations. Somatosens Res 5:259–267

14. Silverman JD, Kruger L (1990) Selective neuronal glycocon- jugate expression in sensory and autonomic ganglia: relation of lectin reactivity to peptide and enzyme markers. J Neurocy- tol 19:789–801

15. Stucky CL, Lewin GR (1999) Isolectin B(4)-positive and -negative nociceptors are functionally distinct. J Neurosci 19:6497–6505

16. Tominaga M, Caterina MJ, Malmberg AB et al. (1998) The cloned capsaicin receptor integrates multiple pain-producing stimuli.

Neuron 21:531–543

17. Villar MJ, Wiesenfeld-Hallin Z, Xu XJ et al. (1991) Further studies on galanin-, substance P- and CGRP-like immunoreactivities in primary sensory neurons and spinal cord: effects of dorsal rhi- zotomies and sciatic nerve lesions. Exp Neurol 112:29–39 18. Wang H, Rivero-Melian C, Robertson G et al. (1994) Trans-

ganglionic transport and binding of the isolectin B4 from Griffonia simplicifolia I in rat primary sensory neurons. Neu- roscience 62:539–551

Immunocytokines

Cytokines, Effects on Nociceptors

Cytokines, Regulation in Inflammation

Immunodeficient

Definition

An innate, acquired, or induced inability to develop a normal immune response.

Animal Models of Inflammatory Bowel Disease

Immunoglobulin Therapy

Definition

Intravenous administration of immunoglobulin has been clinically shown to have anti-inflammatory im- munomodulatory effects in GBS and CIDP. Doses required are higher than those required for immunode- ficiency states.

Inflammatory Neuritis

Immunohistochemistry

Definition

Immunohistochemistry is a staining method using the principle of antigen-antibody interactions to demon- strate a defined protein in tissue sections.

Toxic Neuropathies

Immuno-Inflammatory Muscle Pain

Muscle Pain in Systemic Inflammation (Polymyalgia Rheumatica, Giant Cell Arteritis, Rheumatoid Arthri- tis)

Immunoisolation

Definition

When supplying donor grafted tissue or cells, immunoisolation allows the separation of that tissue from the host, for example in an inert device that cannot be detected by the host immune system. Such a procedure is more likely to lead to long-term survival of donor tissue or cells.

Cell Therapy in the Treatment of Central Pain

Immunoreactivity

Immunostaining

Immunosuppression

Definition

Inhibiting the activation and function of immune cells either by disease, or by drugs.

Proinflammatory Cytokines

Vascular Neuropathies

Impact of Familial Factors on Children’s Chronic Pain

LINDSAYS. UMAN¹, CHRISTINET. CHAMBERS² 1Department of Psychology, Dalhousie University, Halifax, NS, Canada

2Departments of Pediatrics and Psychology, Dalhousie University and IWK Health Centre, Halifax, NS, Canada

luman@dal.ca, christine.chambers@dal.ca

Synonyms

Psychosocial factors; Familial Factors; Parental Re- sponse; Family Environment