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Following a viral prodrome, benign acute (viral) childhood myositis typically presents with muscle tenderness, markedly elevated serum CPK, but preserved muscle bulk, tone, strength, and reflexes; this pattern fits the afebrile 6-year-old in the vignette and is not characteristic of GBS, dermatomyositis, or Duchenne muscular dystrophy [Noma, 2006, PMID 17037368].