Dale E. McFarlin

Primary demyelination in the central nervous system results from damage to the myelin sheath or oligodendroglia and can be produced by a variety of mechanisms, including metabolic disturbances, toxicities, infection, and autoimmunity. The major human demyelinating disease affecting the central nervous system is multiple sclerosis (MS). Although the etiology of MS is not known, existing data indicate that both genetic and environmental factors contribute to pathogenesis. Experimental allergic encephalomyelitis (EAE) is induced by immunization of genetically susceptible animals with myelin proteins. This is mediated by autoimmune T cells. Characterization of MHC restriction, fine specificity of antigen recognition, and T cell receptor (TCR) usage by encephalitogenic T cells has resulted in highly specific immunotherapies. Both HLA and TCR genes have been linked to susceptibility for MS which is widely believed to be mediated by T cells that recognize an as yet unidentified autoantigen. Because of the advances in the understanding and treatment of EAE, recent research in MS has been focused on the characterization of cellular immune responses against myelin components. The results of these studies are reviewed and the potential implications of these findings for the pathogenesis and future therapy of MS are examined.

(First of Two Parts)The lesions of multiple sclerosis were probably described as early as 1838,1 but it was Charcot in 18682 who recognized the characteristic clinical and pathologic features of the disease. Since that time, the disorder has been studied extensively. Numerous distinguished, even renowned physicians and scientists have investigated various aspects of multiple sclerosis. Although much has been learned and many theories have emerged, the cause and pathogenesis of this disease remains unknown. No preventive measures or definitive therapies exist. The purpose of this article is to review the classic clinical and pathologic aspects of the disease and . . .

Magnetic resonance imaging is a highly sensitive method for the detection of the lesions of multiple sclerosis and renders possible the study and the evolution of early lesions. Previous reports on magnetic resonance imaging following gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) injection demonstrated that new lesions can be recognized by contrast enhancement. The pathological basis of these observations is uncertain. We have had the opportunity to study at autopsy the brain of a patient with chronic progressive multiple sclerosis who suffered acute worsening leading to death. Magnetic resonance imaging performed 10 days and 4 weeks prior to death showed new Gd-DTPA-enhanced lesions in the posterior hemispheric white matter adjacent to the lateral ventricles. Light microscopic examination of these areas demonstrated them to be fresh lesions comprising intense inflammatory activity and dense perivascular cuffs within an edematous lesion center and a striking parenchymal mononuclear cell infiltration at the margins of the lesions. Lesions that were demonstrated by increased signal on T2-weighted images, but were not enhanced following administration of Gd-DTPA, were all of the chronic type, either inactive or active. None of these showed the intense inflammatory activity of the acute lesions and most displayed fibrous astrogliosis.

The highly variable clinical course and the lack of a direct measurement of disease activity have made evaluation of experimental therapies in multiple sclerosis (MS) difficult. Recent studies indicate that clinically silent lesions can be demonstrated by magnetic resonance imaging (MRI) in patients with mild relapsing-remitting MS. Thus, MRI may provide a means for monitoring therapeutic trials in the early phase of MS. We studied 12 patients longitudinally for 12 to 21 months with monthly gadolinium (Gd)-enhanced MRIs. The data have been used to identify the most effective design of a clinical trial using Gd-enhanced lesions as the outcome measure. Frequent ( > 1/mo) Gd-enhancing lesions were observed in 9 of the 12 patients, indicating that the disease is active even during the early phase of the illness. The frequency of the lesions was not constant; there was marked fluctuation in lesion number from month to month. However, the magnitude of the peak number of lesions and the frequency of the peaks varied among patients. Because of this variability, the most effective use of Gd-enhancing lesions as an outcome measure in a clinical trial was a crossover design with study arms of sufficient duration to allow accurate estimation of lesion frequency. Monitoring Gd-enhancing lesions may be an effective tool to assist in the assessment of experimental therapies in early MS.