Tryptophan toxicity: a pharmacoepidemiologic review of eosinophilia-myalgia syndrome

Tryptophan, an essential amino acid commercially available as a dietary supplement, has been implicated in the development of a new and potentially fatal clinical entity: eosinophilia-myalgia syndrome (EMS). EMS reached epidemic proportions in the US in late 1989 and early 1990, with 1536 cases and 27 deaths reported as of August 1990. Features of the syndrome include intense, debilitating myalgias and marked peripheral eosinophilia. Vasculitis, neuropathy, and pulmonary involvement also may be observed but are not pathognomonic. Death typically ensues from ascending polyneuropathy with resulting paralysis and respiratory arrest. Treatment involves discontinuation of tryptophan ingestion. Administration of prednisone may not always alleviate or reverse the symptoms. Recovery is generally slow. The etiology of EMS has been traced to a contaminant in the bulk manufacturing process of tryptophan by a single Japanese company. Efforts are currently underway to confirm the structure of the contaminant by laboratory synthesis and to define its biologic and toxic effects using an animal model for EMS.