Continuing occurrence of eosinophilia myalgia syndrome in Canada

Eosinophilia myalgia syndrome (EMS), was defined by the Centers for Disease Control (CDC) as eosinophilia > 1000 mm3 and incapacitating myalgia without infection or neoplasm. Studies suggested that use of L-tryptophan (L-T), was a risk factor. We conducted a pharmacoepidemiological survey in Canada where access to L-T is limited. Using the active surveillance method, a 100% sample of potentially involved specialists and a 15% sample of family physicians from Ontario and Quebec were surveyed regarding treatment of patients with severe myalgia within the past year. Follow-up amplified clinical and laboratory information. Overall response rates were 61.4%. Thirty-eight per cent of respondents reported at least one patient. Of 6423 patients assessed, 19 'definite' and 25 'possible' EMS cases were identified. Information from physicians did not suggest use of L-T in patients with definite or possible EMS. It was considered that the cases found an underestimate of the incidence of EMS. Its continuing occurrence in Canada brings causal interpretations of earlier studies into question.