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© 1997 The Journal of Bone and Joint Surgery, Inc.
Cervical Myelopathy Caused by Bilateral Fibrosis of the Dorsal Root Ganglion in a Patient Who Had Rheumatoid Arthritis. A Case Report* , HOUSTON, TEXASInvestigation performed at The Methodist Hospital, Houston
The cervical spine is frequently involved in patients who have rheumatoid arthritis. The prevalence of involvement of the cervical spine has varied among studies and according to the criteria used to define involvement. Garrod reported that 178 (35.6 per cent) of 500 patients had involvement of the cervical spine, whereas Pellicci et al. reported that forty-six (43 per cent) of 106 patients had such involvement. Conlon et al., using broader criteria for involvement, found a prevalence of 88.6 per cent (295 of 333 patients). Neurological signs, including myelopathy, are less frequently associated with rheumatoid arthritis but have been found in a sizable number of patients. The most common site of involvement of the cervical spine is the atlanto-axial articulation9. Erosion of the atlanto-axial joints and supporting ligaments can lead to subluxation of the first cervical vertebra relative to the second cervical vertebra11. Subaxial instability also has been reported to be a cause of myelopathy7. In addition, synovial pannus can exert a mass effect, further decreasing the space available for the spinal cord6-8,13. Compression of a vertebral artery, vasculitis, arachnoiditis, thrombosis, and dural fibrosis also have been reported to be rare causes of myelopathy in patients who have rheumatoid arthritis3,4,6. We present what we believe to be the first case of myelopathy caused by extradural compression of the spinal cord due to bilateral fibrosis of the dorsal root ganglion of the second cervical nerve in a patient who had rheumatoid arthritis.
A sixty-one-year-old woman who had a thirty-five-year history of severe seropositive rheumatoid arthritis was seen because of increasing weakness and dysesthesias of the upper extremities of one week's duration and the recent onset of a gait disturbance leading to increasing difficulty even with limited walking. Previously, she had been able to walk independently. At the time of the initial examination, the patient was being managed with non-steroidal anti-inflammatory agents, including acetylsalicylic acid and ibuprofen; previously, however, she had needed parenteral administration of corticosteroids and oral administration of chloroquine. On physical examination, the patient was afebrile and had mild hypertension. Evaluation of the musculoskeletal system revealed multiple stigmata of rheumatoid arthritis. On neurological examination, the patient was alert and oriented and had intact cranial nerves. Motor examination demonstrated that the strength of the lower extremities was grade 3 of 5 (able to overcome gravity) and that the strength of the upper extremities was approximately grade 2 of 5 (able to move with gravity eliminated)10. Despite subjective dysesthesias, the sensory examination demonstrated that sharp-dull differentiation was intact (except for some loss of differentiation in the right thumb), as were light touch, proprioception, and vibratory sensation. All of the reflexes in the upper extremities were normal (grade 2 of 4) and symmetrical. The knee reflex was absent on the right because an arthrodesis had been done, and it was grade 2 of 4 on the left. The ankle reflex also was absent on the right but was grade 2 of 4 on the left. The Babinski response was positive bilaterally. The patient was unable to walk because of severe weakness. Laboratory studies demonstrated modest anemia, with a hemoglobin of 104 grams per liter (normal, 120 to 160 grams per liter), a hematocrit of 0.32 (normal, 0.37 to 0.47), and an erythrocyte sedimentation rate of forty millimeters per hour (normal, zero to twelve millimeters per hour). Radiographs made with the cervical spine in flexion and extension revealed only three millimeters of atlanto-axial translation and no evidence of subaxial subluxation or basilar invagination. A myelogram showed mild subaxial stenosis of the cervical spinal canal. A computed axial tomography scan made with myelographic intrathecal contrast medium demonstrated severe degenerative changes surrounding the odontoid process, with hypertrophic spurring of the odontoid process and calcification of the transverse ligament. There was mild anterior subluxation of the atlas on the axis; however, the most remarkable finding on the computed axial tomography scan was severe bilateral impingement of the spinal cord caused by lateral soft-tissue masses at the atlanto-axial junction (Fig. 1). There was substantial attenuation of the subarachnoid space as well as deformity and apparent atrophy of the cephalad portion of the cervical spinal cord. Computed axial tomography scans made at other levels revealed mild stenosis of the spinal canal and of both foramina at the interspace between the third and fourth cervical vertebrae, moderate spinal canal and foraminal stenosis at the interspace between the fourth and fifth cervical vertebrae, and severe spinal canal and foraminal stenosis at the interspace between the fifth and sixth cervical vertebrae. Coronal reconstruction of the computed axial tomography scan of the cephalad portion of the cervical spine confirmed the severe compression of the cord due to bilateral soft-tissue masses (Fig. 2).
Cerebrospinal fluid that was obtained at the time of myelography appeared clear and colorless, and analysis of the fluid revealed only one mononuclear cell per microliter (normal, zero to five mononuclear cells per microliter) and a protein level of 1.14 grams per liter (normal, 0.12 to 0.55 gram per liter). Posterior decompression, accomplished by laminectomy of the second cervical vertebra and bilateral foraminotomy at the first and second cervical levels, was performed on December 29, 1993. After the laminae had been removed, the dura and the bilateral soft-tissue masses were visualized easily. Firm, tan homogeneous soft-tissue masses arose from what were believed to be the dorsal roots of the second cervical spinal nerves; these masses were initially believed to be neurilemmomas, and they were thought to be arising from the dorsal root ganglia because a small nerve entered each mass on one side and exited on the other. Each mass was removed piecemeal until it could be retracted away from the dural sac. After the masses had been removed, intraoperative ultrasonography of the cervical spinal cord demonstrated pulsation of the thecal sac. Histological examination of an intraoperative frozen section revealed benign tissue consistent with a ganglion with fibrosis. Posterior arthrodesis was performed from the first to the third cervical vertebra with use of wire fixation and an autologous unicortical graft of bone from the posterior iliac crest. A halo brace was applied postoperatively. Histological examination of the masses revealed severe fibrosis of the dorsal root ganglia and nerve roots, ganglion-cell dropout, and reactive proliferation of satellite cells. There was approximately 30 per cent of the normal number of ganglion cells per high-power field. The ganglion cells were in clumps and were separated by broad bands of fibrous tissue. The number of satellite cells per ganglion cell was increased compared with those of normal ganglia. Because satellite cells play a supporting role similar to that of astrocytes in the central nervous system or to that of Schwann cells in the peripheral nervous system, this relative increase was interpreted as a reactive proliferation analogous to gliosis. Histological analysis of sections stained with trichrome confirmed the substantial increase in fibrous connective tissue in the ganglion (Fig. 3). There was no compelling evidence of neurilemmoma, neurofibroma, or ganglioneurofibroma. The final diagnosis was bilateral fibrosis of the dorsal root ganglion of the second cervical spinal nerve.
Postoperatively, the patient did well initially. The halo brace was removed at twelve weeks. As of October 15, 1994, there was radiographic evidence of fusion from the first to the third cervical vertebra. On neurological examination, the patient had grade-4 (of 5) strength10 with normal sensation in the upper and lower extremities, although rheumatoid arthritis of the hip and the ankle still made it very difficult to walk. The patient did not report sensory deficits in the region of the second cervical vertebra (the posterior aspect of the scalp), although the sensation appeared to be decreased compared with that in the rest of the scalp.
Neurological signs and symptoms are not commonly associated with rheumatoid arthritis, despite the relative frequency of involvement of the cervical spine. There appears to be no direct relationship between the degree of subluxation and the presence or severity of neurological findings, except when atlanto-axial subluxation is severe (that is, when the posterior atlanto-odontoid interval is less than fourteen millimeters)1. Once neurological signs appear, however, the natural history often is one of progression unless an operation is performed3. To our knowledge, we are the first to report on this very unusual cause of neurological compression without instability in a patient who had rheumatoid arthritis. A proliferative synovial pannus can develop in the atlanto-axial articulations, especially between the transverse ligament and the odontoid process. This tissue can produce a mass effect and act synergistically with any subluxation, leading to compression of the spinal cord. The formation of pannus was considered to be the most likely mechanism of the worsening neurological status in our patient, particularly in view of the very mild atlanto-axial subluxation and the striking appearance of the cervical spine on computed axial tomography scans. At the time of the operation, however, very little pannus was seen and the mass effect was found to be due to the enlarged dorsal root ganglia. There have been reports of other abnormalities leading to neurological compromise in patients who have rheumatoid arthritis. Crellin et al. described kinking of the vertebral arteries that had caused neurological signs. Ferlic et al. described dural fibrosis that had caused compression of the spinal cord. Compression of the vertebral artery, vasculitis, thrombosis, and arachnoiditis have also been reported to cause myelopathy3,4,6. The findings in our patient are very unusual; it is remarkable that the dorsal root ganglia, which are normally located in the far lateral portion of the subarachnoid space (Fig. 4, top), became enlarged enough to cause severe myelopathy (Fig. 4, bottom). After ten months of follow-up, it appeared that posterior decompression with laminectomy, bilateral foraminotomy, and debulking of the mass had been relatively effective for the treatment of the cervical myelopathy caused by bilateral fibrosis of the dorsal root ganglion. However, a longer duration of follow-up is necessary to determine the ultimate effectiveness of treatment.
NOTE: The authors thank Hugh S. Tullos, M.D., and Gregory Hanson, M.D.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
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