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A 46 year old man was first examined in January 1996 for an impairment in the fine movements of his right hand. His history showed an optic retrobulbar neuritis, four years before, with a residual decrease of visual acuity to 6/10 and a pale disc on the left. Neurological examination disclosed only a disturbed stereognosis on his right hand. Visual evoked potentials (EPs) were very abnormal in the left, normal in the right eye. Brainstem auditory EPs and somatosensory EPs were normal. Both MRI of the brain and of the cervical spinal cord failed to show any aspect suggesting plaques. Cervical MRI showed extreme degenerative changes at the C5-C6 and C6-C7 level with a C6-C7 bulging disc. A cross section at the C5-C6 level showed a posterior ostheophyte impressing the subarachnoid space but no areas of abnormal signal intensity within the spinal cord. Analysis of CSF showed a protein concentration of 310 mg/l with gammaglobulins at 21% and oligoclonal banding. Investigation of blood and CSF for infectious and immunological diseases was negative. The diagnosis at discharge was cervical discopathy and possible multiple sclerosis. Two months later the patient complained of a sharp throbbing, burning pain in the first and second finger of his left hand and on the outer side of his left arm, with an intense itching character. At examination scratch lesions drawn on the skin showed the C6 dermatome in its full extension. The bicipital reflex was reduced on the left. Sensory disturbance was limited to hyperalgesia in the C6 dermatome without a clear deficit of specific sensory modalities. Spinal MRI cross section at the C5-C6 level showed in T2 weighted images an area of abnormally high signal intensity within the cord, localised in the left posterolateral and posterior sections and extending to the central region (figure). The spondylosis was unchanged and there was no evidence of spinal or radicular compression.
A left pseudoradicular C6 syndrome, secondary to a fresh plaque of multiple sclerosis in the dorsal root entry zone and posterior horn was diagnosed. Treatment with 1000 mg methylprednisolone/day for three days led to partial improvement. Repetition of the treatment 20 days later led to remission of symptoms.
Pain in multiple sclerosis has been known since 1872, when Charcot referred to shoulder and pelvic girdle pain as symptoms of the disease.1 However, its incidence is variously quoted in the literature, from “uncommon” to 82%.2 Acute pain syndromes include trigeminal neuralgia, paroxysmal burning extremities, painful tonic seizures; chronic pain syndromes include dysaesthetic extremity pain, back pain, and painful leg spasms.3 To our knowledge only two reports are expressly dedicated to radicular pain in multiple sclerosis. Ramirez-Lassepas et al,4during a 15 year span, found 11 patients (3% of the newly diagnosed cases of multiple sclerosis in patients admitted to hospital) who presented with radicular pain and in whom radicular compression was ruled out by imaging techniques; eventually, multiple sclerosis was diagnosed when new neurological symptoms occurred, and was judged to be responsible for the acute radicular pain. In two cases demyelinating plaques within the spinal cord at MRI were thought to be in the appropriate location to explain the radicular (or more properly, pseudoradicular) symptoms. Uldry and Regli5 reported four patients with a formerly diagnosed multiple sclerosis who complained of a radicular limb pain and in whom a relation between the location of one of the plaques shown at MRI and limb pain was postulated. In the present case the relation is unquestionable; in a patient with a possible multiple sclerosis but with previously non-contributory imaging, a single demyelinating plaque appeared within the spinal cord, in the appropriate location to explain the concomitant pain syndrome.
A further note of interest in this case concerns the physiopathology of the pain. The distribution of pain was strictly dermatomeric; however, intense itching, unusual in radicular pain syndromes, suggested a peculiar mechanism. Indeed, a plaque in the dorsal column may generate ectopic bidirectional sensory discharges with abnormal central and antidromic conduction to peripheral endings.6 There is evidence that antidromic impulses cause the release of substance P at the peripheral terminals of primary afferents; substance P in turn has been shown to cause release of histamine from mast cells.7Antidromic conduction and release of histamine could explain the uncommon feature of pain in this case.