Editorial - Mayo Clinic Proceedings, Eosinophilia-Myalgia Syndrome. (Editorial). MAYO CLIN. PROC. 67:1201-1202, DECEMBER, 1992.

Eosinophilia-Myalgia Syndrome


In today's society, a considerable onus is placed on medical practitioners to eradicate all the sufferings that accompany a wide array of physical and emotional illnesses. When these expectations are not met, distressed patients sometimes seek relief in unproven or unorthodox treatments. These avenues often include taking over-the-counter products that are given legitimacy on the basis of testimonials rather than sound scientific studies. They may be promoted as being "natural" and incapable of causing harm. Such was the case with L-tryptophan, an amino acid supplement with a reputation for being a safe remedy for a diverse group of conditions including insomnia, depression, and the premenstrual syndrome.

 In the fall of 1989, a tragedy of epidemic proportions struck some of the users of L-tryptophan products, particularly those living in the United States and, to a lesser extent, residents of Canada and certain European countries. They experienced an acute illness characterized by disabling myalgias and an increased peripheral blood eosinophil count. The disorder was aptly called the "Eosinophilia-Myalgia Syndrome." In many patients, the Eosinophilia-Myalgia Syndrome progressed to a serious multisystem disease with various combinations of fasciitis, sensory and motor neuropathies, myopathy, and interstitial pneumonitis. In some cases, the course was pernicious, and fatalities were caused by a severe ascending neuropathy or aggressive immunotherapy for the illness.

Similarities With Toxic Oil Syndrome - Physicians acquainted with unusual eosinophilic disorders noticed the similarities between the Eosinophilia-Myalgia Syndrome and the toxic oil syndrome that occurred in Spain in 1981. In addition to eosinophilia, the patients with toxic oil syndrome had clinical features and characteristic histopathologic changes in fascia, nerve, and skeletal muscle that were similar to those in patients with the Eosinophilia-Myalgia Syndrome. Toxic oil victims had consumed rapeseed cooking oil instead of L-tryptophan, but a precise cause for the illness was never established.

From the earliest occurrences of both syndromes, the prevailing theory was that ingestion of contaminated products was the primary triggering event. Until now, however, no evidence suggested that one impurity might be responsible for these two epidemics that occurred an ocean and almost a decade apart. In this issue of the Mayo Clinic Proceedings (pages 1134 to 1139), Mayeno and his collaborators update our knowledge about two contaminants in L-tryptophan-containing products. Furthermore, they point out that the more recently discovered contaminant closely resembles analine derivatives present in the implicated Spanish rapeseed oil.

Identification of "Peak E." - Since the discovery of the epidemic of the Eosinophilia-Myalgia Syndrome in the United States in 1989, Mayeno and colleagues have been leaders in researching the cause and pathogenesis of this disorder. Epidemiologic studies implicated the L-tryptophan of a single manufacturer in the epidemic. Investigations into the manufacturing processes of this company disclosed modifications between 1986 and 1989 that failed to remove impurities in bulk L-tryptophan that eventually became available in the marketplace. High-performance liquid chromatography performed on a variety of L-tryptophan products revealed a contaminant called "peak E" in suspect lots but not in case-control or laboratory-grade lots or in L-tryptophan produced by the five other known manufacturers. In due course, peak E was isolated from L-tryptophan. Mayeno and colleagues subjected the peak to stringent analytic methods and determined the chemical structure to be a novel amino acid, 1, I'-ethylidenebis(tryptophan) or EBT.2

Experimental Studies - Results of studies in experimental animals conducted in several research laboratories with use of either implicated L-tryptophan or EBT administered in various dosage regimens and by oral or parenteral routes have been inconclusive and somewhat disappointing. Peripheral blood eosinophilia has not been reliably detected, and the characteristic inflammatory cell exudate in fascia and muscle noted in cases of the Eosinophilia-Myalgia Syndrome has not been reproduced with regularity. As a result of these observations, doubts began to surface about EBT as the most likely contaminant, and some investigators suggested that EBT might be a surrogate for another, as yet unidentified, toxic substance.

Identification of "Peak UV-5" In 1991, investigators in Japan reported the discovery of a second trace contaminant in L-tryptophan, "peak UV-5."  In retrospect, this peak had not been detected in earlier studies of EBT by Mayeno and colleagues because of an unrecognized problem with the timing of sample injections during high-perfonnance liquid chromatographic analyses. With the discovery of this second impurity, the contaminant hypothesis that at one time seemed fairly straight forward became more complex. If two impurities have been detected, might others exist?

 The investigators in Japan did not identify other likely candidates in their studies. The article by Mayeno and co-workers in this issue of the Proceedings does not address this possibility, but the authors tackle problems such as determining- the chemical structure of peak UV-5 and the epidemiologic relationship of the peak with the Eosinophilia-Myalgia Syndrome. On the basis of spectral data, they show that peak UV-5 is 3-(phenylamino)alanine (PAA), as had previously been reported by those who discovered peak UV-5. The precision of this analysis is consistent with previous work by Mayeno and colleagues, in which they demonstrated that the correct chemical structure of peak E was 1,1'ethylidenebis(tryptophan) rather than the di-L-tryptophan aminal of acetaldehyde as reported by others.

The next step involved the actual confirmation of the chemical structure of peak UV-5 as PAA. Independent synthesis of PAA and comparison of the synthetic product with the naturally occurring product by spectral analysis demonstrated that the two were identical.

Epidemiologic Studies -On the basis of epidemiologic analyses, Mayeno and associates established a strong case for an association between PAA and the earlier impurity EBT and also for an association between both amino acids and cases of the Eosinophilia-Myalgia Syndrome. They found measurable quantities of PAA in all lots and of EBT in 96% of the lots of powdered, bulk tryptophan manufactured by the implicated company but not in the products of other manufacturers. Likewise, retail lots of L-tryptophan consumed by patients with the Eosinophilia-Myalgia Syndrome contained higher concentrations of PAA and EBT than did control lots; moreover, in the month before onset of the disease, patients with the Eosinophilia-Myalgia Syndrome consumed significantly greater quantities of PAA and EBT than did control subjects.

Unfortunately, although the epidemiologic analysis establishes a convincing association between PAA and EBT on the one hand and between both impurities and the cases of Eosinophilia-Myalgia Syndrome on the other, it does not reveal which substance initiated the onset of the illness. The culprit could be either impurity alone, an as yet unidentified substance, or even a metabolic product of any of these contenders. The failure to develop a satisfactory animal model with eosinophilia-myalgia features with use of EBT favors another trigger, and PAA emerges as the most attractive candidate on the basis of current knowledge. PAA provides laboratory investigators with a new tool to repeat and to extend previous studies in search of cytokines that cause eosinophilia and an experimental animal model that demonstrates typical histopathologic lesions. If PAA fails to pass scientific muster, then metabolites of these amino acids or other impurities must be sought.

Valuable Link -Perhaps one of the most exciting observations in the current report by Mayeno and associates is the structural similarity between PAA and the 3-phenylamino1,2-propanediol impurity found in implicated rapeseed Oil from Spain. Although scientists have not determined whether interconversion is possible between PAA and 3phenylamino-1,2-propanediol or whether this chemical has the same epidemiologic relationship to toxic oil as PAA has to L-tryptophan, an extraordinary opportunity has been provided for reconciliation of two disorders that were not thought to have a common cause. Mayeno and colleagues may be well on their way toward affirming that our scientific world continues to shrink when neither time nor distance deters investigators who have the will to persevere.

Rationale for Further Investigations - After review of the current status of our understanding of two contaminant triggered epidemic illnesses, it is reasonable to question whether scientists should continue to study two erst while syndromes when the damaging products are no longer available. Nevertheless, a few cogent justifications for further investigations can be emphasized. Good scientists never leave a problem only partially solved, especially when patients are still ill and when additional leads are unexplored. Two devastating epidemics of similar illnesses occurred less than 10 years apart; a third could possibly strike at any time, and the medical community should be adequately prepared to treat and to investigate in such a situation. Scientific information gleaned from these studies will be exceedingly helpful for providing better insight into the role of environmental agents in connective tissue diseases and for elucidating pathogenic mechanisms in similar illnesses without known etiologic factors.

Conclusion - In coming decades, physicians must be challenged to become better informed about the products their patients consume. Awareness of the potential for these products to cause harm as well as to produce benefit is essential. The health and welfare of future generations must be safeguarded against harm from products presumed to be safe and wholesome.

Joseph Duffy, M.D.
Division of Rheumatology
and Internal Medicine
Mayo Clinic
Rochester, Minn.


I . Belongia EA, Hedberg CW, Gleich GJ, White KE, Mayeno AN, Loegefing DA, Dunnette SL, Pifie PL, MacDonald KL, Osterholm MT: An investigation of the cause of the eosinophilia-myalgia syndrome associated with tryptophan use. N Engl J Med 323:357-365, 1990

2. Mayeno AN, Lin F, Foote CS, Loegefing DA, Ames MM, Hedberg CW, Gleich GJ: Characterization of "peak E," a novel amino acid associated with eosinophilia-myalgia syndrome. Science 250:1707-1708, 1990

3 . Toyo'oka T, Yamazaki T, Tanimoto T, Sato K, Sato M, Toyoda M, Ishibashi M, Yoshihira K, Uchiyama M: Characterization of contaminants in EMS-associated L-tryptophan samples by high-per-formance liquid chromatography. Chem Pharm Bull (Tokyo) 39:820-822, 1991