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The discovery that striated skeletal muscle and cardiac muscle could be the sole targets of a number of infectious agents came about during the era of the development of microbiology and occupied the attention of many prominent clinicians, including Osler. As these diseases were being characterized, however, a number of other inflammatory states affecting muscle were found for which there was no infectious cause. Later, an autoimmune mechanism was postulated, but even today this is not securely established. This group of idiopathic inflammatory myopathies figures so prominently in clinical myology that we devote a chapter to the subject. First, the infections of muscle are described.

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Included here are trichinosis, toxoplasmosis, parasitic and fungal infections, and a number of viral infections. The related but unclassifiable entity of sarcoid myopathy is addressed at the end of the chapter.

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Trichinosis

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This parasitic disease is caused by the nematode Trichinella spiralis. Its general features are discussed in Chap. 32. With respect to the myopathic aspect of the illness, the authors have been most impressed with the ocular muscle weakness, which results in strabismus and diplopia; with weakness of the tongue, resulting in dysarthria; and with weakness of the masseter and pharyngeal muscles, which interferes with chewing and swallowing. Any weakness of limb muscles is usually mild and more severe proximally than distally. However, the diaphragm may be involved, as well as the myocardium. The affected muscles are slightly swollen and tender in the acute stage of the disease. Often, there is conjunctival, orbital, and facial edema, sometimes accompanied by subconjunctival and subungual splinter hemorrhages. As the trichinae become encysted over a period of a few weeks, the symptoms subside and recovery is complete. Many, perhaps the majority, of infected patients are asymptomatic throughout the invasive period, and as much as 1 to 3 percent of the population in certain regions of the country will be found at autopsy to have calcified trichinella cysts in their muscles with no history of parasitic illness. Heavy infestations have been known to end fatally, usually from cardiac and diaphragmatic involvement. In these more massive infections, the brain also may be involved, probably by emboli that arise in the heart from an associated myocarditis.

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Diagnosis

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Clinically, one should suspect the disease in a patient who presents with a puffy face and tender muscles. Eosinophilia is practically always present in the peripheral blood (>700 cells/mm3), although the sedimentation rate is often normal. The creatine kinase (CK) level is moderately elevated. A skin test using Trichinella antigen is available but it is unreliable. The enzyme-linked immunosorbent assay (ELISA) blood test is more accurate but it becomes positive only after 1 or 2 weeks of illness. Biopsy of almost any muscle (usually the deltoid or gastrocnemius), regardless of whether it is painful or tender, is probably the most reliable confirmatory test. More than 500 mg of muscle may ...

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