Diagnosis of OPLL and OYL: Overview Masato Tanaka

Diagnosis of OPLL and OYL: Overview

Masato Tanaka ¹ , Atsunori Kanazawa ² , and Kazuo Yonenobu ³

Introduction

The radiographic diagnosis of ossifi cation of the poste- rior longitudinal ligament (OPLL) is not diffi cult once a physician understands the disease entity in question.

However, the diagnostic workup of OPLL is not simple.

Depending on the condition of the patient, a functional assessment—such as evaluation of neurological symp- toms, prediction of the progression of OPLL, investiga- tion of associated diseases, and prognostication of treatment—should be performed.

The Committee for the Development of Clinical Prac- tice Guidelines for OPLL has systematically reviewed the diagnosis of OPLL. Because of the nature of the diagnosis, most studies are transverse or case series, so the level of supporting evidence is not high. However, detailed observation studies are signifi cant and clini- cally valuable.

History

Obtaining a history, especially regarding the following in regard to OPLL, is important: family history, episode of trauma, mode of progression, and duration of symp- toms before treatment. Approximately 30% of siblings of patients with OPLL develop OPLL to a variable extent, and genetic factors are believed to be the etiology of this condition [1]. Episodes of trauma in relation to the development or progression of symptoms is important.

Although a history of trauma has not been defi ned as a predictor of poor outcome [2–4], it is a risk factor for spinal cord injury [5,6].

Clinical Manifestations

Symptoms caused by cervical OPLL are those of cervi- cal myelopathy and cervical radiculopathy, axial dis- comfort around the neck, and limitation of neck motion.

About 45% of patients with OPLL have motor dysfunc- tion of the extremities, which might impair their life- style [7]. Matsunaga et al. reported that about 40% of symptomatic patients presented with myelopathy [8].

According to a nationwide survey, the symptoms are pain/numbness of the upper limb in 74%, neck/nuchal pain in 64%, changes of refl exes in the lower limbs in 58 %, sensory change in the upper limbs in 55%, and changes of refl exes in the upper limbs [9].

The initial symptoms of ossifi cation of the yellow ligament (OYL) are usually numbness or tingling dys- esthesia in the feet or legs and sometimes diffi culty walking. A girdle sensation or tightness of the trunk or legs, a dull pain in the back, and a stiff spine are some- times accompanying symptoms. The main pathology of clinical symptoms is mechanical compression of the spinal cord and nerve roots; the dynamic factor associ- ated with movement of the spine is less involved. In addition, OYL is frequently accompanied by OPLL at other levels. The incidence of the association of cervical OPLL with thoracolumbar OYL is 44.9% [10] and often gives rise to complex motor symptoms. Motor impair- ment is more severe in patients with tandem cervical and thoracic lesions than with an isolated cervical lesion.

Imaging Diagnosis

Plain Radiography

Usually, OPLL is diagnosed on lateral plain radiographs as an abnormal radiopacity along the posterior aspects of the vertebral bodies. According to the Investigation Committee on OPLL of the Japanese Ministry of Health and Welfare, OPLL is radiographically classifi ed into four types on the basis of the sagittal plane appearance:

1

Department of Orthopaedic Surgery, Okayama University Medical School, 5-1 Shikata-cho, 2-Chome, Okayama 700- 8558 , Japan

2

Department of Orthopaedic and Rheumatic Surgery, National Hospital Organization, Osaka-Minami Medical Center, 2-1 Kidohigashi, Kawachinagano, Osaka 586-8521, Japan

3

Vice-Director, National Hospital Organization, Osaka- Minami Medical Center, 2-1 Kidohigashi, Kawachinagano, Osaka 586-8521, Japan

111

112 M. Tanaka et al.

continuous, segmental, mixed, localized (Fig. 1). The segmental type is most common, occurring in 39% of patients with OPLL. The absolute anteroposterior canal diameter does not always parallel the degree of spinal cord signs; yet patients with space available for the spinal cord (SAC) who have <9 mm on fi lms of the cer- vical spine can develop severe spinal cord symptoms [11,12]. All patients with an SAC <6 mm have presented with myelopathy. Canal stenosis due to the ossifi ed masses is the essential factor of spinal cord compres- sion in such patients. In contrast, patients with an SAC

>14 mm have never presented with myelopathy. Patients with an SAC of >6 mm but <14 mm do not always present with myelopathy. Segmental motions of the cer- vical spine in these patients play an important role in the onset of myelopathy [13].

Computed Tomography

Computed tomography (CT) is much more sensitive than plain radiography and is thus indispensable for visualizing the detailed outline of an ossifi ed mass. On CT scans, OPLL is observed as an ossifying mass, usually as dense as bone, lying dorsal to the vertebral bodies or discs. Reconstruction CT is particularly helpful for determining the thickness, coronal and sagittal exten- sion, the shape of the OPLL, and the extent of narrow- ing of the spinal canal by OPLL. Therefore, CT is valuable when planning surgical intervention.

Magnetic Resonance Imaging

Because magnetic resonance imaging (MRI) is less sen- sitive and less specifi c for the diagnosis of an ossifi ed or calcifi ed mass, its principal use is in the assessment of associated cord compression and intramedullary cord lesions such as cord edema and myelomalacia.

MRI can be more sensitive than CT when distinguish- ing whether a hypertrophic posterior longitudinal liga-

ment adjacent to the dura is or is not associated with OPLL. The correlation between the cross-sectional area of the spinal cord on MRI and postoperative outcomes has been investigated [14–16]. The cross-sectional area of the spinal cord on preoperative MRI cannot always predict postoperative recovery. However, the postop- erative/preoperative ratio of the cross-sectional area of the spinal cord on MRI positively correlates with the postoperative outcome. High signal intensity in the spinal cord on T2-weighted images is thought to rep- resent edema, demyelination, myelomalacia, cavita- tion, and necrosis. A high-intensity signal in the spinal cord also correlates with the severity of the myelopathy [17,18].

Metabolic Background

The incidence of OPLL is high in patients with meta- bolic and endocrinological disorders, including dis- rupted mineral metabolism by conditions such as hypoparathyroidism and vitamin D-resistant hypo- parathyroidism rickets/osteomalacia, disturbed glucose metabolism, and altered sex hormones and growth hormone secretion or action [19,20]. Although none of the metabolic or endocrinological disturbances play a causative role in the development of OPLL, accumulat- ing evidence indicates that disturbed bone and mineral metabolism that alters the actions of systemic hor- mones might underlie the progression of OPLL.

Among the metabolic factors, abnormal glucose tolerance is signifi cant. Harata reported that the inci- dences of OPLL in patients with or without diabetic mellitus are 15.9% and about 2.0%, respectively [21].

Details of the metabolic background of OPLL are described elsewhere in this book. Although the inci- dence of associated diabetes mellitus is high, an oral glucose tolerance test is not mandatory for a diagnosis of OPLL.

Electrodiagnosis

With OPLL, lesions develop as a result of compression by multiple ossifi ed masses, and diagnosing the main lesion in the cervical spine by neurological examination alone is sometimes diffi cult. Electrodiagnostic proce- dures help identify lesions in the nervous system when used in combination with a radiographic examination.

Kaneko et al. [22] performed an electrophysiological study of patients with OPLL using evoked spinal cord potentials (ESCPs). They concluded that ESCPs brought about by stimulating the median nerve or spinal cord and by transcranial electrical stimulation are useful for identifying the most critical lesions.

Fig. 1. Type of OPLL

Diagnosis of OPLL and OYL: Overview 113

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