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To the Editor.—
Tepperberg (238:27, 1977) describes the clinical and laboratory course in eight boys of an acute illness diagnosed as transient acute myositis on clinical and laboratory grounds. The possibility of Guillain-Barré syndrome was suspected. However, one important differential test, that of electrodiagnosis, was not used.In fact, the differentiation of neuropathy from myopathy is one of the principal aims of an electrodiagnostic evaluation. The tests used include motor and sensory nerve conduction measurement and electromyography.Motor nerve conductions remain entirely within normal limits in the myopathies, although in severe myopathies the responses may be of low amplitude. The sensory nerve conductions and responses are unaffected in the myopathies. In the Guillain-Barré syndrome, motor and sensory conductions should be altered very early in the disease, both in conduction speed and amplitude.Electromyography differs in these two types of involvement principally in the findings on voluntary contraction. The myopathies are
Rogoff JB. Transient Acute Myositis in Children. JAMA. 1977;238(17):1813. doi:10.1001/jama.1977.03280180017013