Microangiopathy in the eosinophilia-myalgia syndrome. The eosinophilia-myalgia syndrome associated with the ingestion of L-tryptophan was recognized in late 1989. We describe our pathologic study of skin, fascial, and muscle biopsies from 21 patients evaluated by light microscopy, histochemistry, and electron microscopy. A perivascular, lymphocytic infiltrate with eosinophils was present in the dermis, fascia, and skeletal muscle. Lymphocytic infiltration of arteries and arterioles was seen. Ultrastructurally, capillary and arteriolar endothelial cell thickening and necrosis was present. This microangiopathy suggests that ischemia may be a contributing factor to the findings in this syndrome. 