Sarcopenia

Sarcopenia is a progressive, generalised loss of skeletal muscle mass, strength and function that accompanies ageing and chronic disease. Low muscle strength is now regarded as the key feature, with low muscle quantity or quality confirming the diagnosis.

Depending on the definition, 10% to 16% of older adults are affected, and the proportion rises steeply after 75. It is common in hospital and nursing home residents.

Pathophysiology. Anabolic resistance blunts the muscle response to protein and exercise. Motor unit loss with denervation, satellite cell dysfunction, mitochondrial decline, insulin resistance, chronic inflammation, low vitamin D and low sex hormones all contribute, and inactivity and poor intake accelerate the loss.

Weakness, slow walking, difficulty rising from a chair and climbing stairs, fatigue, falls and reduced independence. Weight may be stable because fat gain masks muscle loss. Consequences include fractures, admissions, disability and early death.

Probable sarcopenia is low grip strength (under 27 kg in men and under 16 kg in women) or a slow five time chair stand (over 15 seconds). Confirm with low appendicular lean mass by dual energy X-ray absorptiometry (under 7.0 kg/m2 in men and under 5.5 kg/m2 in women) or bioimpedance. Severe sarcopenia adds slow gait (0.8 m/s or less). Exclude secondary causes with creatine kinase, thyroid function, calcium, vitamin D, vitamin B12, glucose, renal and liver tests.

Differential diagnosis.

• Cachexia from cancer, heart failure, COPD or chronic kidney disease.
• Statin or corticosteroid myopathy, inflammatory myopathy and polymyalgia rheumatica.
• Hypothyroidism, hyperthyroidism and hypercortisolism.
• Motor neuron disease and neuropathy.

Progressive resistance exercise 2 to 3 times weekly is the main treatment, ideally combined with balance work. Give protein 1.0 to 1.2 g/kg daily (20 to 30 g at each meal) and enough energy to avoid weight loss. Replace vitamin D when the level is low. Stop myotoxic drugs where possible. No drug has proven benefit, and testosterone and anabolic agents are not advised for sarcopenia alone.

Monitoring. Grip strength and gait speed every 3 to 6 months.