L-tryptophan and eosinophilia-myalgia syndrome in New Mexico

On Oct 30, 1989, the New Mexico Health and Environment Department learned of 3 patients with eosinophilia and severe myalgia who had been taking L-tryptophan. Further review of these and similar cases led to the initial recognition of the eosinophilia-myalgia syndrome (EMS) epidemic. To elucidate the apparent association between L-tryptophan-containing products (LTCPs) and EMS a case-control study was done. The case definition was unexplained peripheral eosinophilia (2000/μl or more) and incapacitating myalgia. Cases were found through review of white blood cell counts from May 1 to Oct 31, 1989, in nine medical laboratories in New Mexico. 11 cases and 22 matched controls were interviewed for information on symptoms and other clinical findings, on the use of LTCPs, and on potential confounding factors. All 11 cases (100%) used LTCPs compared with only 2 controls. These findings led to a ban on the sale of LTCPs in New Mexico, followed by a nationwide recall of such preparations in the United States.