There are a number of primary immune mediated neuromuscular diseases. Careful clinical examination, detailed neurophysiological studies and muscle immunohistochemistry are key to accurate diagnosis and effective therapy. The archetypical disease, myasthenia gravis, is most often caused by autoantibodies to nicotinic acetylcholine receptors (AChR-abs) and is clearly initiated in the thymus. However, the antigens and antigen presenting cells that determine the immunopathogenesis of other immune myopathies is unclear. “Myositis specific antibodies” are found in the great majority of patients with “overlap myositis” and in dermatomyositis, but their antigenic targets are not muscle-specific and their specificity is related more closely to involvement of tissues other than muscle. Muscle-specific autoantibodies have been found in only two immune myopathies to date: anti-decorin myopathy (antibodies to chondroitin sulphate, a component of the muscle extracellular matrix) and in myositis with antibodies to γ/δ sarcoglyan. Muscle inflammation is a common histopathological finding in a wide variety of muscle diseases in addition to immune myopathies. It is probable that such inflammation plays a part in the pathogenesis of genetic myopathies which, in turn, can be associated with autoantibodies such as AChR-ab that contribute to the muscle dysfunction. Increasingly, efforts are being made to identify muscle-specific autoantibodies using muscle specific antigen sources in a variety of conditions.
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