It has been known for a long time that there is an association of some sort between thymic lesions, thymomas in particular, and myasthenia gravis.1 More recently, cross-reactions have been demonstrated between antimuscle antibodies in the sera of individuals suffering from myasthenia gravis and certain cells of the thymus.2,3 There is little doubt that the reactive elements in the thymus are not entodermal reticular elements, but actual muscle cells, the "myoidzellen" of the old anatomists.4
Elongated, occasionally stellate, eosinophilic cells containing cross-striated fibrils have been reported among thymocytes and reticular cells of the thymus in a variety of vertebrates. First described by Mayer5 in the frog's thymus, they were observed by him as long, spindle-shaped elements showing distinct striations and closely resembling rudimentary skeletal muscle fibers. Pensa6 found these strange cells to be particularly numerous and well developed in the thymus of chickens and called
Van de Velde RL, Friedman NB. The Thymic "Myoidzellen" and Myasthenia Gravis. JAMA. 1966;198(3):287–288. doi:10.1001/jama.1966.03110160115033
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