Friday, 14 October 2011

Alcohol myopathy

In response to recent bedside teaching on a middle-aged man with alcoholic cerebellar degeneration. He also had evidence of a proximal myopathy. 

Level 2: Urbano-Marquez et al. The effects of alcoholism on skeletal and cardiac muscle. N Engl J Med. 1989 Feb 16;320(7):409-15.

This study was performed to determine the prevalence of alcoholic myopathy and cardiomyopathy. They studied a group of 50 asymptomatic alcoholic men (mean age, 38.5 years) entering an outpatient treatment program. Studies performed included an assessment of muscle strength by electronic myometer, muscle biopsy, echocardiography, and radionuclide cardiac scanning, with comparison to healthy control subjects of similar age. The patients' mean (+/- SEM) daily alcohol consumption was 243 +/- 13 g over an average of 16 years. These patients had no clinical or laboratory signs of malnutrition or electrolyte imbalance. 42% of the patients, as compared with none of the controls, had strength of less than 20 kg as measured in the deltoid muscle. Muscle-biopsy specimens from 23 patients (46%) had histologic evidence of myopathy. In the cardiac studies, when the alcoholic patients were compared with 20 healthy controls, the patients had a significantly lower mean ejection fraction (59% vs. 67%), a lower mean shortening fraction (33 vs. 38 percent), a greater mean end-diastolic diameter (51 vs. 49 mm), and a greater mean left ventricular mass (123 vs. 106 g per square meter of body-surface area). One third of the alcoholics had an ejection fraction of 55 percent or less, as compared with none of the controls. Endomyocardial biopsy specimens from six patients with ejection fractions below 50 percent showed histologic changes of cardiomyopathy. The estimated total lifetime dose of ethanol correlated inversely with muscular strength (r = -0.65; P less than 0.001). In an analysis that also included six patients with symptomatic alcoholic cardiomyopathy, the estimated total lifetime dose of ethanol correlated inversely with the ejection fraction (r = -0.58; P less than 0.001) and directly with the left ventricular mass (r = 0.59; P less than 0.001). The Investigators' conclude that myopathy of skeletal muscle and cardiomyopathy are common among persons with chronic alcoholism and that alcohol is toxic to striated muscle in a dose-dependent manner.

"This study illustrates how common alcoholic myopathy is and in my experience it is often missed at the bedside. The best way to screen for it is to: (1) test power of shoulder abduction, (2) ask the patient to attempt a sit-up with arms folded across the chest and (3) to perform a squat. These manoeuvres typically bring out proximal and truncal weakness."

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