Muscle fiber type-2 atrophy neuropathy

Vignette 1. Type-2 muscle-fiber atrophy, neoplasm-related cachectic atrophy, plus sensory-motor neuropathy... 

Proximal muscle weakness in an elderly patient associated with a normal electromyogram (EMG) can be caused by type-2 muscle fiber atrophy, which is diagnosable only on muscle biopsy. One should seek an identifiable cause, such as cachexia, disuse, glucocorticoid toxicity, a "remote" neoplasm, hyperparathyroidism, subtle denervation, or supra-segmental central nervous system (CNS) abnormality. This mainly-sensory nerve neuropathy can cause slowed sensory nerve conductions, if involving large diameter fiber, small diameter ones. 

In HIV there is often a complex pathogenesis of the muscle atrophy, which histochemically is type-2 fiber atrophy with or without denervation atrophy. It can have five components (a) neuropathic, viz. dysimmune dysschwannian denervation neuropathy early in the course of the disease, and virogenic toxicity causing dysneuronal neuropathy later (b) often cachexia (c) hypomotUity/disuse (d) possible nerve toxicity of anti-HIV dmgs (e) infrequently, myotoxicity from viral products. With HIV, type-2 fiber atrophy in response to a hyponutri-tional/cachectic aspect would be altmistic, but when in response to the other causes it would not be. 

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