Clinical Manifestation of Cervical OPLL Kazuo Kaneko

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Clinical Manifestation of Cervical OPLL

Kazuo Kaneko

Introduction

Ossiﬁ cation of the posterior longitudinal ligament (OPLL), which is most frequently found at the cervical spine, causes several symptoms. OPLL can be detected on lateral plain radiographs, and the diagnosis and morphological details of cervical OPLL have been clearly demonstrated by magnetic resonance imaging (MRI) and computed tomography (CT).

The shape and volume of OPLL are quite varied.

OPLL is sometimes found in a limited area but often extends over a wide area behind the posterior wall of the vertebral body and disc of the spine, occupying anywhere from less than 10% to more than 50% of the anterior portion of the spinal canal. OPLL is classiﬁ ed into four types on lateral plain radiography: (1) seg- mental; (2) continuous; (3) mixed; (4) localized [1,2].

The shape is also quite irregular. OPLL is one of the most signiﬁ cant lesions that compromise the spinal canal, causing compression of the spinal cord and the nerve roots in various ways.

Because of the varied shape and volume of the OPLL, the clinical syndrome manifests differently among indi- viduals. Clinical symptoms and signs caused by cervical OPLL are categorized as: (1) cervical myelopathy, or a spinal cord lesion with motor and sensory disturbance of the upper and lower limbs, spasticity, and bladder dysfunction; (2) cervical radiculopathy, with pain and sensory disturbance of the upper limbs; and (3) axial discomfort, with pain and stiffness around the neck.

Usually these syndromes are combined to various degrees. Cervical myelopathy, or a spinal cord lesion, is the essential syndrome because OPLL basically com- presses the spinal cord under the narrow spinal canal, and the compressed cord produces severe disturbance of the activities of daily living [3,4].

The clinical syndrome of cervical OPLL mostly develops insidiously, and the time of onset is usually unclear.

However, occasionally there is an acute spinal cord

injury after an accidental fall or a hyperextension force to the neck. Rarely, OPLL is found while screening during a medical checkup of a patient with no symptoms. When OPLL is found in a person who has no symptoms or discomfort, the ossifi cation is considered to be a radiographic fi nding in the spine, such as a degenerative change. The formation and growth of OPLL are thought to occur slowly, so OPLL is not always symptomatic. In cases in which cervical OPLL is found by radiography, the syndrome might manifest at various degrees of severity—from no symptoms to severe paralysis. The clinical entity of cervical OPLL can be defi ned as neurological complaints or defi cits or as annoying discomfort around the neck originating from the compressed or entrapped neural tissues caused by OPLL of the cervical spine.

Incidence of OPLL and Clinical Survey

Based on research on OPLL sponsored by the Japanese Ministry of Health and Welfare, OPLL is found in about 1%–2% of the total population in Japan [1,5]. In the other reports, cervical OPLL has been found in 1.9%–

4.3% of the Japanese population [6]. Mongoloid or Asian people seem to have a frequency similar to that in Japan. According to previous reports, the incidence of OPLL in Japan is relatively higher than that in the United States or European nations, although its incidence is similar to that in Utah in the United States (1.3%) [7]. More epidemiological studies are needed, however, to determine the actual incidence of OPLL in various countries. No particular region was found to predominate regarding the incidence of OPLL in Japan.

Therefore, some genetic background is suspected in OPLL formation.

The average age at the onset of symptoms is about 50 years. OPLL is not reported in children or adolescents.

About 70% of patients are 45–65 years of age. The frequency gradually increases at ages above 40 years, with the greatest frequency in those in their ﬁ fties. Cervical OPLL has a male predominance of 2 : 1, whereas thoracic OPLL is more frequently seen in women.

Department of Orthopaedic Surgery, Yamaguchi University School of Medicine, 1-1-1 Minami-Kogushi, Ube 755-8505, Yamaguchi, Japan

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No speciﬁ c type of physical constitution or occupa- tion was reported for the patients. It remains unclear, however, if obesity and diabetes mellitus inﬂ uence the incidence of OPLL. Several systemic metabolic back- grounds (e.g., growth hormone, sex hormone) have been proposed to play a causative role in OPLL. For example, patients with OPLL have a higher incidence of diabetes than the overall population and may have coexisting hypoparathyroidism, acromegaly, vitamin D-resistant rickets, spondyloepiphyseal dysplasia, and myotonic muscular dystrophy.

Although there is little clinical signifi cance, ossifi cation of other ligamentous structures outside the spinal canal—including the anterior longitudinal ligament, supraspinous ligament, and nuchal ligament—is frequently seen. There is consensus that clinicians must make note of the fact when the patient has concomitant OPLL or ligamentum fl avum (OLF) at other spinal levels. Reportedly, 9%–17% of patients with cervical OPLL have OPLL, OLF, or both at other spinal levels, so there is a question of whether those lesions are responsible for the myelopathy.

Clinical Features

No speciﬁ c symptoms and signs of cervical OPLL are reported. Approximate 45% of patients with cervical OPLL have some neurological symptoms, and 16.8% of patients need help with their activities of daily living;

5% of patients have no symptoms [1]. Electrophysio- logic assessment using somatosensory evoked poten- tials and transcranial magnetic stimulation is useful for detecting the presence and severity of cervical myelopathy. The clinical features of cervical OPLL were noted in a previous edition of this book [7]. In general, the most common complaint at the onset (Table 1) is par- esthesia or numbness of the hands. Neck pain or discomfort around the neck and clumsiness of the fi ngers are the next most common symptoms. The complaints then gradually increase and extend to the lower limbs, which leads to diffi culty walking. Most patients visiting the clinic show spastic involvement of the lower extrem- ities with an increase in the deep tendon refl exes, frequently the presence of Babinski’s sign, and sensory changes in the limbs (Table 2).

Based on an analysis of 262 patients with cervical OPLL at the fi rst visit to our clinic, the symptoms were neck/nuchal pain in 69% of patients, pain/numbness of the upper limbs in 67%, motor weakness/clumsiness of the upper limbs in 42%, pain/numbness of the lower limbs in 39%, motor weakness of the lower limbs or diffi culty with gait in 41%, and bladder/rectal disturbance in 16%. In the upper limbs, the neurological signs were changes in refl exes (biceps and triceps tendon

refl exes) in 59% (hyperrefl exia 52%, hyporefl exia 7%), positive Hoffman’s refl ex in 41%, and sensory change in 56%. Those in the lower limbs were hyperrefl exia of the patellar or ankle tendon refl exes (or both) in 57%, positive Babinski’s refl ex in 25%, and sensory changes in 37%. There was a distinct difference in the laterality in 27% of patients.

Myelopathy and Radiculopathy

The pathophysiology of cervical myeloradiculopathy (Table 3) is mechanical compression of the spinal cord and nerve roots. OPLL plays a role as a static compression factor; and intervertebral motion, as the dynamic factor, has an important role in the progression of neurological symptoms [8]. The incidence of myelopathy ranges from 20% to 50% in cervical OPLL patients, who complain of some clinical symptoms. OPLL is seen in about 25% of patients with cervical myelopathy in Table 1. Initial symptoms of cervical ossiﬁ cation of the posterior longitudinal ligament at the onset and their frequency (%)

Symptoms Frequency (%)

Neck and nuchal pain/stiffness 46: 46 (neck) Pain/numbness of upper limb 39

Sensory change (upper limb) 10: 59 (upper limb) Weakness/clumsiness (upper limb) 10

Pain/numbness of lower limb 14

Weakness/clumsiness (lower limb) 10: 30 (lower limb) Sensory change (lower limb) 6

Data are percentages of cases

Table 2. Symptoms and signs at the time of the ﬁ rst visit to the clinic

Symptoms and signs Frequency (%)

Neck/nuchal

Pain/stiffness 69

Upper limb

Pain/numbness 67

Sensory change 56

Motor weakness/clumsiness 42

Reﬂ ex changes 59

Hoffmann-positive 41

Lower limb

Pain/numbness 39

Sensory changes 37

Motor weakness/difﬁ cult gait 41

Hyperreﬂ exia 57

Positive Babinski sign 25

Bladder/rectal disturbance 16

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Japan and North America [1,9]. Two major scales are used worldwide for judging the severity of myelopathy:

the Nurick scale [10] and the Japanese Orthopaedic Association (JOA) scale. The Nurick myelopathy scale offers six grades of neurological classiﬁ cation: grade 0, intact, mild radiculopathy without myelopathy; grade I, mild myelopathy; grade II, mild to moderate myelopathy; grade III, moderate myelopathy; grade IV, moderate to severe myelopathy; grade V, severe myelopathy, quadriplegia. The JOA score is described in the other section.

Abnormal patterns of reﬂ exes in upper limbs, distribution of muscle weakness, and distribution of numbness or sensory disturbance is useful for detecting the symptomatic intervertebral level for myelopathy, such as cervical spondylotic myelopathy. In some patients with complicating thoracic OPLL or OLF (or both), it is difﬁ cult to diagnose the level responsible for the myelopathy. In such cases, electrophysiologic assessment can be helpful.

Unlike the symptoms and signs of cervical spondylotic or discogenic radiculopathy, radiculopathy due to OPLL is vague; and the deﬁ nition of radiculopathy is not easy. Therefore, the reported incidence of radiculopathy in cervical OPLL shows great variation.

Axial Discomfort

The patients often present with dull pain and neck stiffness. These symptoms are felt in the middle of the neck and spread to the suboccipital region or across the shoulder, where the sensation may seem to emanate from the levator scapulae muscles. The pains are mostly vague and mild, unlike those of cervical disc disorder.

Neck motion is often limited or severely stiff, espe- cially in patients with large continuous-type OPLL. The axial discomfort may originate from stimulation of the sinuvertebral nerve spreading in the posterior longitudinal ligament or constriction of the nerve root in the canal; however, the exact origin remains unclear.

Natural Course and Development of Myelopathy

Myelopathy caused by cervical OLL develops gradually, or occasionally there is deterioration after an accident.

According to a report of a 10-year follow-up, 17% of patients without myelopathy evident at the fi rst examination developed myelopathy during the follow-up period. Risk factors associated with the development of myelopathy included more than 60% OPLL-induced stenotic compromise of the cervical canal and increased range of motion (ROM) of the cervical spine. The space available for the spinal cord (SAC) and the ROM of the cervical spine are important factors for the development of myelopathy. Pathological compression by the ossifi ed ligament above a certain critical point (<6 mm of SAC) may be the most signifi cant factor in inducing myelopathy, whereas below that point dynamic factors may be largely involved in inducing myelopathy.

Surgery has proved effective for the management of patients with moderate or severe myelopathy [8]. A minor traumatic event is known to be a risk factor for aggravation of neurological symptoms. In a retrospec- tive investigation of 552 patients with OPLL, 24 patients (13%) identiﬁ ed cervical trauma as the trigger of their myelopathy. In the prospective investigation, 70% of patients did not develop myelopathy over a follow-up of more than 20 years. Only 6% of 368 patients without myelopathy at the time of the initial consultation sub- sequently developed trauma-induced myelopathy [11].

It is thought that prophylactic surgery prior to the onset of myelopathy is unnecessary in most patients with OPLL.

OPLL grows slightly larger on radiographic observa- tion in about 40%–60% of the cases. Growth in length is to either the rostral or caudal side, and growth in thickness is inward to the canal side. Continuous-type or mixed-type OPLL tends to grow larger than the seg- mental type. Although OPLL grows slowly and not always relative to the severity of the clinical symptoms, in some cases it becomes evident during a long-term follow-up (Fig. 1). Some reports have noted that certain surgical procedures were believed to have a harmful effect on the growth of OPLL. OPLL development has been observed in about 70% of patients who undergo posterior surgery, a relatively higher incidence than in those who undergo an anterior procedure.

Conclusions

Cervical OPLL is sometimes encountered in Japan, but it does not always correlate with the severity of the patient’s clinical symptoms. About 45% of patients with Table 3. Frequency of each syndrome

Syndrome Frequency (%)

Myelopathy 45

Neck/shoulder pain 25

Posttraumatic cord lesion 10

Radiculopathy 7

Combined 13

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cervical OPLL have various clinical syndromes related to compression of the spinal cord or cervical nerve roots (or both). The clinical entity cervical OPLL is deﬁ ned as a condition eliciting neurological complaints or deﬁ cits or annoying discomfort around the neck originating from compressed or entrapped neural tissues caused by OPLL of the cervical spine.

The onset of symptoms is insidious, and myelopathy mostly progresses slowly. Occasionally, an acute spinal cord lesion, similar to a central cord lesion, occurs after minor trauma. The severity of the preexisting myelopathy, SAC, and the ROM of the cervical spine are important factors for myelopathy development.

References

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Fig. 1. Lateral plain radiograph shows marked development of ossiﬁ cation of the posterior longitudinal ligament (OPLL) at the 10-year follow-up

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