Eosinophilia-myalgia syndrome in patients ingesting a single source of L-tryptophan.

OBJECTIVE: To estimate the attack rate for eosinophilia-myalgia syndrome and to identify potential risk factors for illness among patients attending a New York City medical clinic, who purchased L-tryptophan containing products produced exclusively by Showa Denko K.K.

METHODS: A case-control design was used. Cases and controls purchased L-tryptophan containing products at the medical clinic from July 1, 1989--December 1, 1989. All case-patients identified with illness onset during the study period were included. Controls were selected by a systematic sample of the 683 purchasers of L-tryptophan attending the same clinic.

RESULTS: Twelve (2.2%) of an estimated 553 L-tryptophan users were case-patients. Multivariate analysis suggested that lot 2 use (adjusted odds ratio [OR] = 35.9), concomitant use of chromium (adjusted OR = 12.3), and concomitant use of pyridoxine (adjusted OR = 5.8) were associated with the development of illness. Chemical analysis of tablets corresponding to the 3 Showa Denko K.K. lots ingested by study participants showed that lot 2 had the highest concentration of ethylidenebis (L-tryptophan), a proposed causative agent or marker for a causative agent in the eosinophilia-myalgia syndrome.

CONCLUSIONS: Information from our study of persons exposed to implicated L-tryptophan supports the role for a contaminant as the causative agent in the eosinophilia-myalgia syndrome and identifies possible cofactors that deserve further study.