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Eosinophilia-Myalgia Syndrome in L-Tryptophan—Exposed Patients

Mary L. Kamb, MD, MPH; John J. Murphy, MD; Jeffrey L. Jones, MD, MPH; J. Christopher Caston, MD; Kees Nederlof, MD; Louise F. Horney, MD, MSPH; Leslie A. Swygert, MD, MPH; Henry Falk, MD, MPH; Edwin M. Kilbourne, MD
JAMA. 1992;267(1):77-82. doi:10.1001/jama.1992.03480010085029.
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Objectives.  —To study the incidence of eosinophilia-myalgia syndrome, the risk factors associated with the syndrome, and the clinical spectrum of illness associated with L-tryptophan use in an exposed population.

Design.  —Retrospective cohort and nested case-control studies of risk factors for eosinophilia-myalgia syndrome using inpatient and outpatient chart reviews, telephone interviews, and in-person patient interviews. Descriptive study of clinical course of L-tryptophan users.

Setting.  —Office practice of one psychiatrist based in a small city (population 43467) in South Carolina.

Patients.  —Eligible subjects were all patients from the practice who used L-tryptophan during the 1989 study interval. Of these, 418 (87%) were interviewed.

Main Outcome Measures.  —Clinical spectrum of illness associated with L-tryptophan use, including definite and possible cases of eosinophilia-myalgia syndrome.

Results.  —Among the 418 interviewed L-tryptophan users, we identified 47 definite cases (11%) and 68 possible cases (16%) of eosinophilia-myalgia syndrome, most of which involved patients who were using one retail brand of L-tryptophan (brand A). Among the 157 brand A users, we identified 45 definite cases (29%) and 36 possible cases (23%) of eosinophilia-myalgia syndrome, and the risk for the syndrome increased as the brand A dose increased. Fifty percent (19 of 38) of those using more than 4000 mg/day developed definite eosinophilia-myalgia syndrome, and 84% (32 of 38) developed either definite or possible eosinophilia-myalgia syndrome. On multivariate analysis, risk for definite eosinophilia-myalgia syndrome was associated with brand A dose and age of the patient; however, gender, race, and use of other medications were not associated with the syndrome.

Conclusions.  —These results suggest that many people exposed to the agent causing eosinophilia-myalgia syndrome may develop illness, and dose of presumably contaminated L-tryptophan is the single most important predictor of eosinophilia-myalgia syndrome. The broad range of signs and symptoms reported by patients using L-tryptophan illustrates that a strict case definition may identify only about half of those affected.(JAMA. 1992;267:77-82)


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