5. The patient has diffuse myalgia and fatigability. Most such patients have proved to be depressed and only rarely to have a myopathy. A few will be found to be caused by a toxic myopathy, particularly from one of the statin class of drugs. Hypothyroidism, McArdle disease, hyperparathyroidism, steroid myopathy, adrenal insufficiency, and early rheumatoid arthritis must be excluded by appropriate studies. Features that virtually exclude a myositis are (1) lack of reduced peak power of contraction and (2) normal EMG, serum enzymes, and muscle biopsy.
6. Trichinosis, toxoplasmosis, HIV, and other infectious causes of myositis can simulate acute immune myositis as described in the early parts of this chapter. Occasionally, the diagnosis of sarcoidosis is made from the muscle biopsy, but the myopathic features (weakness and pain) tend to be minor.
There are a large number of unrelated myositides and rare forms of focal myositis or relatively minor changes in muscle that occur in the course of inflammatory diseases of blood vessels or systemic infections and, curiously, with certain tumors such as thymoma. Most of these do not warrant extensive consideration and are described in detail in monographs devoted to muscle disease (see Banker). We are uncertain how to place the newly described and undoubtedly rare entity of myositis with abundant macrophage infiltration and aluminum hydroxide crystalline deposits. A type of fasciitis that is characterized by pronounced infiltration of macrophages has been related to vaccinations that contain the aluminum compound, but the myositis does not seem to be related to this aforementioned entity (see Bassez et al).
Three inflammatory myopathic diseases, however, are distinctive and of interest to neurologists: (1) eosinophilic myositis, fasciitis, and myalgia syndrome, (2) orbital myositis, and (3) sarcoidosis of muscle.
This term has been applied to 4 overlapping clinical entities: (1) eosinophilic fasciitis, (2) eosinophilic monomyositis (sometimes multiplex), (3) eosinophilic PM, and (4) the eosinophilia-myalgia syndrome.
Eosinophilic fasciitis This condition, mistakable for PM, was reported by Shulman in 1974. He described 2 men with a scleroderma-like appearance of the skin and flexion contractures at the knees and elbows associated with hyperglobulinemia, elevated sedimentation rate, and eosinophilia. Biopsy revealed greatly thickened fascia, extending from the subcutaneous tissue to the muscle and infiltrated with plasma cells, lymphocytes, and many eosinophils; the muscle itself appeared normal and the skin lacked the characteristic histologic changes of scleroderma. One of Shulman’s patients recovered in response to prednisone.
The many reports that followed have substantiated and amplified Shulman’s original description. The disease predominates in men in a ratio of 2:1. Symptoms appear between the ages of 30 and 60 years and are often precipitated by heavy exercise (Michet et al). There may be low-grade fever and myalgia followed by the subacute development of diffuse cutaneous thickening and limitation of movement of small and large joints. In some patients, proximal muscle weakness and eosinophilic infiltration of muscle can be demonstrated (Michet et al). Repeated examinations of the blood disclose an eosinophilia in most but not all patients. The disease usually remits spontaneously or responds well to corticosteroids. A small number relapse and do not respond to treatment and some have developed aplastic anemia and lymphoor myeloproliferative disease.