Muscle Wasting (Muscle Atrophy): Causes and Treatment

What muscle wasting looks like

• Thinner arms or legs, or loss of shape in the shoulders, buttocks or thighs
• One limb smaller than the other
• Hollowing between the bones of the hand or at the base of the thumb
• Weakness: difficulty climbing stairs, getting out of a chair, opening jars or lifting
• Tiring quickly
• In nerve-related wasting: twitching under the skin (fasciculations), cramps, numbness or tingling

Causes of muscle wasting

Disuse atrophy

Muscles adapt to how much they are used. Without regular loading, they lose protein quickly. Even a week of bed rest can cause measurable loss of leg muscle, and older adults lose muscle faster. Causes include bed rest, hospital and intensive care stays, a cast or brace, sedentary lifestyle, and conditions such as arthritis that make movement painful. Disuse atrophy is reversible with exercise.

Aging (sarcopenia)

Sarcopenia is age-related loss of muscle mass and strength. Muscle mass declines gradually from around age 40 and faster after 65 to 70. It raises the risk of falls, fractures, disability and loss of independence. Resistance exercise and adequate protein slow and partly reverse it.

Malnutrition and chronic illness

• Cachexia: a wasting syndrome in advanced cancer, heart failure, COPD, kidney disease, HIV and other chronic diseases, driven by inflammation. It causes loss of muscle even when eating. See cachexia.
• Low protein or calorie intake, eating disorders, poor absorption from celiac disease or bowel disease.
• Critical illness: intensive care stays cause rapid wasting and weakness.

Medicines and hormones

• Long-term corticosteroids such as prednisone cause steroid myopathy, mainly affecting the thighs and upper arms.
• Hormone problems: an overactive thyroid, Cushing's syndrome, low testosterone and poorly controlled diabetes.
• Alcohol misuse causes muscle damage (alcoholic myopathy).

Nerve damage

When a nerve is damaged, the muscles it supplies waste away. This is called neurogenic atrophy and is often limited to one area.

• Carpal tunnel syndrome: wasting at the base of the thumb with numbness in the thumb, index and middle fingers.
• Ulnar nerve entrapment at the elbow: wasting between the thumb and index finger and of the small hand muscles, with numbness in the little finger.
• Pinched nerve roots in the neck or lower back.
• Peripheral neuropathy from diabetes or other causes, often wasting the feet and lower legs.
• Nerve injuries from trauma.

Nerve and muscle diseases

• ALS (motor neuron disease): progressive wasting and weakness, often starting in one hand or foot, with twitching and cramps, and later slurred speech and swallowing problems. Sensation is normal.
• Spinal muscular atrophy: inherited loss of motor nerve cells, usually starting in infancy or childhood.
• Muscular dystrophies: inherited diseases that progressively weaken muscles. Duchenne muscular dystrophy affects boys, starting in early childhood.
• Inflammatory myopathies: polymyositis, dermatomyositis and inclusion body myositis.
• Guillain-Barré syndrome, polio and post-polio syndrome.

Clues to the cause

How doctors find the cause

A doctor will ask when the wasting started, how fast it is progressing, about activity, diet, weight loss, medicines, alcohol, numbness and family history. They will compare limb sizes, test strength, reflexes and sensation, and look for twitching.

Tests can include:

• Blood tests: creatine kinase (CK, a muscle enzyme), thyroid function, glucose, vitamin levels, inflammation markers, kidney and liver function
• Nerve conduction studies and electromyography (EMG) to show whether the problem is in the nerves or muscles
• MRI of the spine, nerves or muscles
• Muscle biopsy for suspected muscle disease
• Genetic testing for inherited conditions
• Body composition scans (DEXA) to measure muscle mass, and grip strength testing for sarcopenia

Treatment and rebuilding muscle

Exercise

Resistance (strength) training is the most effective way to rebuild muscle. Train each major muscle group 2 to 3 times a week, using weights, resistance bands or body weight (sit-to-stands, step-ups, wall push-ups). Start gently and progress gradually. A physical therapist can design a safe program, especially after illness, injury or surgery. Aerobic activity such as walking builds endurance.

Nutrition

• Eat enough protein: many older adults benefit from about 1.0 to 1.2 g of protein per kg of body weight per day, spread across meals, unless a doctor has advised otherwise (for example in kidney disease).
• Make sure overall calories are adequate.
• Check vitamin D, and treat deficiency.
• Nutritional supplements can help people who cannot eat enough.

Treating the cause

• Reduce or stop medicines such as steroids where possible.
• Treat thyroid, hormone or nutritional problems.
• Release trapped nerves (for example carpal tunnel surgery) before wasting becomes permanent.
• Specialist treatments for ALS, spinal muscular atrophy and muscular dystrophies, including newer gene-targeted therapies for some conditions.

Frequently asked questions

Can muscle atrophy be reversed?

Disuse atrophy and age-related muscle loss can often be largely reversed with regular resistance exercise and enough protein. Wasting from long-standing nerve damage or progressive diseases such as ALS is harder to reverse, but therapy can maintain function. Early treatment gives the best results.

How quickly do muscles waste away?

Muscle loss begins within days of inactivity. Studies show measurable loss of leg muscle after a week or two of bed rest or immobilization, and older adults lose muscle faster. Recovery usually takes longer than the loss, often weeks to months of training.

What causes muscle wasting in the hands?

Wasting at the base of the thumb is often caused by carpal tunnel syndrome. Wasting of the small hand muscles between the fingers often comes from ulnar nerve compression at the elbow or a pinched nerve in the neck. Progressive hand wasting with twitching and no numbness can be an early sign of ALS.

What is the difference between muscle wasting and muscle weakness?

Muscle wasting means the muscle has shrunk in size. Muscle weakness means it produces less force. They usually occur together, but weakness can happen without visible wasting, for example in myasthenia gravis or early nerve problems, and wasting can be subtle before weakness is noticed.