Multiple sclerosis is the most common demyelinating disease. Although the cause remains unknown, current pathogenetic theory postulates an autoimmune phenomenon in response to an insult--possibly viral in nature--to the central nervous system. The lesions of multiple sclerosis are mimicked in experimental allergic encephalomyelitis, an autoimmune disease induced in animals by immunization with myelin.
The hallmark pathologic lesion of multiple sclerosis is a plaque in the central nervous system; 90 percent of these plaques occur in the white matter. Acute plaques are characterized by edematous periventricular inflammation containing T lymphocytes, plasma cells and macrophages. Acute plaques are thought to reflect disease activity. Chronic plaques show astroglia proliferation and demyelination.
Multiple sclerosis mainly affects young caucasian adults, with the mean age of onset in the third and fourth decades. Women comprise a slight majority of cases (60 percent). Migrational trends and the increased incidence of multiple sclerosis in temperate climate zones implicate an environmental factor, which may be geographically distributed. High familial incidence, high concordance in monozygotic twins and HLA antigen associations suggest that genetic factors influence disease susceptibility.
The clinical presentation of multiple sclerosis depends on the anatomic location of the lesions. Multiple neurologic signs and symptoms are possible. Monocular vision loss and disturbances of gait and sensation are the most common symptoms at presentation.
Approximately 40 percent of patients with multiple sclerosis experience an episode of retrobulbar optic neuritis, characterized by vision loss (usually central scotoma) and pain on movement of the eye. Conversely, many patients with isolated optic neuritis develop multiple sclerosis in the ensuing 15 years; rates for progression to multiple sclerosis range from 15 percent to 85 percent.
Corticospinal and sensory tract involvement may manifest as upper motorneuron spasticity, paresthesia or pseudobulbar palsy. Cerebellar involvement produces scanning dysarthria, titubation, intention tremor or gait ataxia. Brainstem findings include diplopia, internuclear ophthalmoplegia, trigeminal neuralgia and nystagmus.
Internuclear ophthalmoplegia is caused by a lesion of the medial longitudinal fasciculus between the midpons and oculomotor nucleus. On lateral upward gaze, the abducting eye develops nystagmus, and there is incomplete adduction of the other eye. Although vascular disease is the most common cause of internuclear ophthalmoplegia in older patients, multiple sclerosis is the most frequent cause in young adults, especially when it is bilateral.
Bladder dysfunction and transverse myelitis may occur with spinal cord involvement. Affective disorders and cognitive impairment are now recognized with increasing frequency in patients with multiple sclerosis.
The diagnosis of multiple sclerosis is based primarily on clinical grounds. The current diagnostic classification is based on a composite of clinical and laboratory data. Ancillary evaluation, which includes neuroimaging and evoked potentials, is used to identify occult lesions that are not apparent on the neurologic examination.
Clinical evidence of more than one lesion and symptoms of multiple sclerosis that occur on more than one occasion are diagnostic. Few patients meet these criteria early in the disease course; therefore, detection of subclinical lesions by magnetic resonance imaging (MRI) is important.
Evoked potentials may also be helpful in the diagnosis, but the findings are neither as sensitive nor as specific as MRI.[1,4] However, when abnormalities are not detected on MRI, evoked potentials may be especially useful in assessing the visual system. In addition, visual evoked potentials may be abnormal in patients without visual symptoms but with occult optic involvement. In this case, evoked potentials may be helpful in confirming the diagnosis of multiple sclerosis. For example, 30 to 40 percent of patients with multiple sclerosis have MRI-detectable lesions isolated to the spinal cord. In these patients, visual evoked potentials may provide confirmatory evidence of multiple sclerosis.
Cerebrospinal fluid oligoclonal banding, an immunochemical test, is nonspecific but provides supportive data when the diagnosis is elusive. In CSF studies, the IgG index and synthesis rate are more specific than oligoclonal bands. Central nervous system lupus and neurosyphilis, for example, commonly produce positive oligoclonal bands. MRI findings do not necessarily correlate with evoked potentials and CSF findings.
MRI is the modality of choice to support the clinical diagnosis of multiple sclerosis. [T.sub.2]-weighted images, especially the first echo of a [T.sub.2]-weighted sequence, are the most sensitive for detecting the plaques of multiple sclerosis, which usually appear as focal regions of [T.sub.2] hyperintensity. A periventricular and/or callosal distribution is characteristic (Figure 1). Infratentorial, spinal cord and optic nerve lesions are commonly demonstrated (Figure 2), because of excellent tissue contrast, multiplanar capability, surface coils and lack of bone artifact.
Although standard [T.sub.1]-weighted images are frequently normal, intravenous gadolinium-DPTA--enhanced [T.sub.1]-weighted images are sensitive to disruption of the blood-brain barrier and therefore can demonstrate active, or acute, multiple sclerosis plaques (Figure 3). Thus, MRI can distinguish acute lesions (enhancement with gadolinium on [T.sub.1]) from chronic lesions (no gadolinium enhancement on [T.sub.1]). Diffuse cortical and/or callosal atrophy and decreased [T.sub.2] signal in the thalamus and putamen are other nonspecific findings. The decrease is reported in patients with advanced multiple sclerosis, presumably secondary to iron accumulation, which decreases the
The sensitivity of MRI for detection of multiple sclerosis lesions is 90 to 97 percent; the percentage increases with the clinical certainty of diagnosis. Specificity has improved but remains suboptimal. Lesions involving the inferior aspect of the corpus callosum and callosal-septal interface may have a specificity level as high as 98 percent. The radiologic differential diagnosis (Table 1) can be narrowed significantly by clinical and laboratory correlation.
Because of rapid technologic advances, MRI has a potential beyond its current role in multiple sclerosis imaging. Quantitative lesion analysis can be used to estimate lesion load and evaluate experimental therapies. Ultrafast imaging may improve multiple sclerosis screening efficiency. Proton MR spectroscopy may help to elucidate the biochemical alterations in multiple sclerosis lesions.
No current therapy alters the natural history of the disease, which most commonly has a relapsing/remitting and unpredictable course. For the most part, patients show progressive residual neurologic deficits and disability. Corticosteroids and adrenocorticotropic hormone (ACTH) are the most widely used medications in the treatment of symptomatic exacerbations, but their efficacy is questionable. Other pharmacotherapy is directed toward alleviating specific symptoms.
Current experimental therapies include immunomodulation, azathioprine (Imuran), cyclophosphamide (Cytoxan, Neosar), copolymer 1, cyclosporine (Sandimmune), beta interferon (Betaseron), plasmapheresis and total lymphoid irradiation. Beta interferon is an orphan drug.
Comprehensive care extends far beyond pharmacologic treatment and involves physical and occupational therapy, psychologic assessment, social services and patient education.
[1.] Mikulis D, Kuhn M. Multiple sclerosis. In: Taveras JM, et al, eds. Radiology: diagnosis, imaging, intervention. Philadelphia: Lippincott, 1992:1-11. [2.] Swanson JW. Multiple sclerosis: update in diagnosis and review of prognostic factors. Mayo Clin Proc 1989;64:577-86. [3.] Petersen RC, Kokmen E. Cognitive and psychiatric abnormalities in multiple sclerosis. Mayo Clin Proc 1989;64:657-63. [4.] Uhlenbrock D, Seidel D, Gehlen W, et al. MR imaging in multiple sclerosis: comparison with clinical, CSF, and visual evoked potential findings. AJNR Am J Neuroradiol 1988;9:59-67. [5.] Wallace CJ, Seland TP, Fong TC. Multiple sclerosis: the impact of MR imaging. AJR Am J Roentgenol 1992;158:849-57. [6.] Gean-Marton AD, Vezina LG, Marton KI, et al. Abnormal corpus callosum: a sensitive and specific indicator of multiple sclerosis. Radiology 1991;180:215-21. [7.] Rudick RA, Goodkin DE, Ransohoff RM. Pharmacotherapy of multiple sclerosis: current status. Cleve Clin J Med 1992;59:267-77. [8.] Goodkin DE, Ransohoff RM, Rudick RA. Experimental therapies for multiple sclerosis: current status. Cleve Clin J Med 1992;59:63-74.
COPYRIGHT 1993 American Academy of Family Physicians
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