Alcoholic skeletal muscle myopathy: definitions, features, contribution of neuropathy, impact and diagnosis.

Alcohol misusers frequently have difficulties in gait, and various muscle symptoms such as cramps, local pain and reduced muscle mass. These symptoms are common in alcoholic patients and have previously been ascribed as neuropathological in origin. However, biochemical lesions and/or the presence of a defined myopathy occur in alcoholics as a direct consequence of alcohol misuse. The myopathy occurs independently of peripheral neuropathy, malnutrition and overt liver disease. Chronic alcoholic myopathy is characterized by selective atrophy of Type II fibres and the entire muscle mass may be reduced by up to 30%. This myopathy is arguably the most prevalent skeletal muscle disorder in the Western Hemisphere and occurs in approximately 50% of alcohol misusers. Alcohol and acetaldehyde are potent inhibitors of muscle protein synthesis, and both contractile and non-contractile proteins are affected by acute and chronic alcohol dosage. Muscle RNA is also reduced by mechanisms involving increased RNase activities. In general, muscle protease activities are either reduced or unaltered, although markers of muscle membrane damage are increased which may be related to injury by reactive oxygen species. This supposition is supported by the observation that in the UK, alpha-tocopherol status is poor in myopathic alcoholics. Reduced alpha-tocopherol may pre-dispose the muscle to metabolic injury. However, experimental alpha-tocopherol supplementation is ineffective in preventing ethanol-induced lesions in muscle as defined by reduced rates of protein synthesis and in Spanish alcoholics with myopathy, there is no evidence of impaired alpha-tocopherol status. In conclusion, by a complex series of mechanisms, alcohol adversely affects skeletal muscle. In addition to the mechanical changes to muscle, there are important metabolic consequences, by virtue of the fact that skeletal muscle is 40% of body mass and an important contributor to whole-body protein turnover.