Isolated Inflammatory Demyelinating Cns Syndromes

Region-restricted episodes of CNS inflammatory demyelination in persons without prior symptoms often represent the initial manifestation of MS, although some may be a forme fruste of ADEM (see later). The probability of recurrent demyelinating episodes has been the subject of several important investigations, and several clinical features and test results are of predictive value. Optic nerve, spinal cord, and brain stem are the most common sites of these recurrent monosymptomatic events, and the time profile follows that of MS relapses. The pathogenesis, pathophysiology, epidemiology, clinical features, associated disorders, differential diagnosis, evaluation, and management are the same as in MS and are discussed previously.

In these cases, the prognosis for visual recovery after each episode of optic neuritis is good and most patients regain normal visual acuity. Profound visual loss, recurrent optic neuritis, and age older than 35 are associated with a

higher risk for poor recovery. Investigators have concluded that recurrent multifocal demyelinating episodes, fulfilling the diagnostic requirements of CD MS, develop in 50 percent or more of patients after isolated optic neuritis when follow-up is extended beyond 20 years. y Most of this risk is incurred within the first few years, although significant risk may continue into the fourth decade after the event. Children much more often develop simultaneous bilateral optic neuritis and have a lower risk for subsequent MS than adults. Factors that are associated with an increased risk of developing MS as a disseminated illness are the presence of venous sheathing, recurrent optic neuritis, family history of MS, white race, previous vague or nonspecific neurological symptoms, and the presence of OCBs, elevated IgG index, or IgG synthesis rate in CSF. Head MRI gives the most strongly predictive information. The relative risk of one or more cerebral white matter lesions, found in approximately 50 percent of optic neuritis patients, is 3 to 14. Of the 44 patients with monosymptomatic optic neuritis in one study, 82 percent of those with abnormal MRI fulfilled the diagnosis of MS within 5 years whereas only 6 percent of those with normal or nonspecific findings on MRI developed MS. y The Optic Neuritis Treatment Trial also found an increased risk of MS in those with cerebral white matter lesions on MRI (27.7 percent of those with an abnormal head MRI vs. 9.3 percent of those with a normal head MRI after 3 years of follow-up). y Both of these studies found that a higher number of lesions correlated with an even greater risk of MS.

The severity of acute transverse myelitis is inversely related to the risk of acquiring further symptomatic demyelinating lesions. Complete transverse myelitis with profound loss of motor, sensory, and sphincter function imparts a relatively low risk of 3 to 14 for the later diagnosis of MS. Partial transverse myelitis with preservation of significant motor function at peak is associated with a much higher incidence of MS. Head MRI further delineates the risk. In a study by Ford and associates, 11 of 12 patients with partial transverse myelopathy and cerebral white matter lesions on MRI developed MS within 3 years of follow-up whereas only 1 of the 3 patients with normal MRI progressed to MS.y Excluding the 2 patients with complete transverse myelopathy in Morrissey's study, 59 percent of the patients with an isolated spinal cord syndrome and abnormal head MRI met the criteria for MS during a 5-year follow-up and 11 percent of patients with normal MRI had recurrences of multifocal demyelination. y

Although monosymptomatic brain stem demyelination is not as common as either optic neuritis or acute transverse myelitis, similar conclusions have been reached. In the only study available, two thirds of these patients with cerebral white matter lesions detected on MRI developed MS within 5 years, compared with none of 5 patients with normal head MRI.y


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