Eosinophilic monomyositis Painful swelling of a calf muscle or, less frequently, some other muscle has been the chief characteristic of this disorder. Biopsy discloses inflammatory necrosis and edema of the interstitial tissues; the infiltrates contain large but variable numbers of eosinophils. The disorder was typified by 1 of our patients, a young woman who developed such an inflammatory mass first in 1 calf and, 3 months later, in the other. The response to prednisone was dramatic; the swelling and pain subsided in 2 to 3 weeks and her power of contraction was then normal. When the connective tissue and muscle are both damaged, a chaotic regeneration of fibroblasts and myoblasts may result, forming a pseudotumorous mass that may persist indefinitely.
Eosinophilic polymyositis Layzer and associates described an eosinophilic disorder that they classified as “subacute polymyositis.” Their patients were adults in whom predominantly proximal weakness evolved over several weeks. The features of the muscle disorder were typical of PM except that the inflammatory infiltration was predominantly eosinophilic and the muscles were swollen and painful. Moreover, the muscle disorder was part of a widespread systemic illness typical of the hypereosinophilic syndrome. The systemic manifestations included a striking eosinophilia (20 to 55 percent of the white blood cells), cardiac involvement (conduction disturbances and congestive failure), vascular disorder (Raynaud phenomenon, subungual hemorrhages), pulmonary infiltrates, strokes, anemia, neuropathy, and hypergammaglobulinemia. There was a favorable response to corticosteroids in 2 patients, but in a third the outcome was fatal in 9 months. Layzer and coworkers noted that a lack of necrotizing arteritis distinguished this process from polyarteritis nodosa and Churg-Strauss disease. No infective agent was isolated. An allergic mechanism seems possible, and in the present authors’ view one cannot exclude an angiitis as a cause of the muscle lesions.
The last two of these previously mentioned syndromes (eosinophilic monomyositis and polymyositis) have overlapping features as shown by Stark’s cases, in which a monomyositis was accompanied by several of the systemic features described by Layzer and colleagues. An uncertain proportion of cases are attributable to mutations in CAPN3, the gene for calpain-3 (Krahn et al). Moreover, some cases of eosinophilic polymyositis without systemic features have been found to be limb-girdle muscular dystrophy 2A, also due to a calpain mutation (i.e., both are considered to be “calpainopathies”). Patients with the dystrophic process, who also have a peripheral eosinophilia, probably have eosinophilic myositis.
Eosinophilia-Myalgia syndrome Beginning in 1980, sporadic reports documented a lingering systemic illness characterized by severe generalized myalgia and eosinophilia of the peripheral blood following the ingestion of contaminated l-tryptophan. In late 1989 and early 1990, an outbreak occurred of this eosinophilia-myalgia syndrome, as the illness came to be called. More than 1,200 cases were reported to the Centers for Disease Control and Prevention (Medsger) and we examined several of them. The outbreak was ultimately traced to the use of nonprescription l-tryptophan tablets used as a sleep aid supplied by a single manufacturer and contaminated by ethylidene-bis- carboxylic acid, both close chemical relatives of l-tryptophan (Mayeno et al, 1990, 1992).