Pathologic manifestations of the eosinophilia myalgia syndrome: analysis of 11 cases

We describe the histopathologic changes of skin, muscle, vessels, and fascia in 11 patients with eosinophilia myalgia syndrome, a newly described entity that has been linked to the ingestion of L-tryptophan. This syndrome is defined clinically by severe incapacitating myalgias and a peripheral eosinophilia. Arthralgias, edema of the extremities, morbilliform rashes, skin induration, weakness, fatigue, and respiratory weakness may be present as well. The earliest apparent histologic changes were observed at the septa between subcutaneous fat lobules and in the deep dermis or fascia. The septa and fascia were infiltrated with a sparse mixture of lymphocytes and histiocytes. In the deep fascia, in addition to inflammatory cells, there were distinctive, reactive mesenchymal cells that showed features of both histiocytes and fibrocytes. Minimal tissue eosinophilia was seen despite the extent of blood eosinophilia. Dermal thickening and homogenization of collagen bundles occurred with replacement of fat and adnexa (changes indistinguishable from scleroderma or morphea). Vessel walls in the dermis and fascia showed thickening and endothelial swelling, but no overt vasculitis was noted. Skeletal muscle biopsies showed a perimysial, epimysial, and/or fascial inflammatory infiltrate of lymphocytes and distinctive reactive mesenchymal cells with some eosinophils. Minimal myofiber atrophy, regeneration, or necrosis was seen despite the clinical history of severe myalgias in almost all patients. This syndrome should help gain insight into the mechanisms of fibrosis in environmental-induced, scleroderma-like syndromes and in idiopathic, scleroderma-like disorders as well.