Discussion Author(s): 2 Lt Duojia Xu
Multiple sclerosis (MS) is a multifocal disease with a complex pathogenesis that includes inflammation and potentially disabling focal lesions that disseminate throughout the central nervous system. It is the most common primary myelin disorder, with an estimated patient prevalence of 250,000 to 350,000 in the United States. Eighty percent of patients have relapsing-remitting MS, and the minority of patients has primary progressive MS. This subtype of MS usually begins in the second or third decade of life and has a female predominance of approximately 2:1. The prevalence is highest in northern Europe, however, the occurrence of rapid shifts in the incidence of MS have been reported in recent studies.
The pathogenesis of MS remains unclear today. However, a multifactorial pathogenetic mechanism has been postulated given the heterogeneity of clinical, genetic, and radiological studies of MS. The pathological hallmark of chronic MS is the demyelinated plaque, which consisted of a well-demarcated hypocellular area characterized by the loss of myelin, relative preservation of axons, and the formation of astrocytic scars. Lesions have a predilection for the optic nerves, periventreicular white matter, brain stem, cerebellum, and spinal cord white matter. Lesions are usually round or ovoid, thought they may also have finger-like extensions along the path of small or medium-sized blood vessels (Dawsonâ€™s fingers).
The diagnosis of multiple sclerosis is based on established clinical, laboratory and radiological findings. Patients with the relapsing forms of multiple sclerosis usually present with sensory disturbances, unilateral optic neuritis, diplopia, limb weakness, gait ataxia, and neurogenic bladder and bowel. Prominent cortical signs and extrapyamidal phenomena can also present but are rarely predominant features of the clinical presentation. Laboratory workup typically includes a cerebrospinal fluid analysis, which often shows increased intrathecal synthesis of immunoglobulins of restricted specificity (oligoclonal bands of IgG) with moderate lymphocytic pleocytosis. Cole and colleagues have suggested that the presence of oligoclonal bands in cerebrospinal fluid slightly increases the risk of recurrent disease.
MRI is the preferred imaging modality to study suspected MS as it depicts the frequency, shape, and location of the characteristic MS lesions. These lesions have discrete foci with well-defined margins that are commonly located in a periventricular location, in the deep white matter, adjacent to the atria, occipital horns, and the body of the lateral ventricles. T2-weighted images reflect a broad spectrum of pathological changes, including inflammation, edema, demyelination, gliosis, and axonal loss. Many of the hyperintense T2-weighted lesions have little clinical significance, as they are more likely to be chronic MS lesions. Hence, there is no correlation with the number of brain lesions detected with a T2-weighted sequence and the patientâ€™s level of functional disability. Studies have shown that fluid-attenuated inversion recovery (FLAIR) sequences are superior to T2-weighted images for detecting MS brain lesions as it can detect many cortical and juxtacortial lesions in MS, which may present in secondary progressive disease and often missed by other sequences. Furthermore, gadolinium-DTPA injection, a paramagnetic contrast agent that crosses only disrupted blood-brain-barrier, may demonstrate foci of demyelination.
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