Corticosteroid Myopathy

A muscular disorder that results from administered corticosteroids or intrinsic cortisol excess.

Corticosteroid myopathy results from prolonged corticosteroid therapy--often given for conditions that themselves cause muscle weakness (eg, myasthenia gravis, inflammatory myopathy)--or from conditions associated with elevated corticotropin levels (eg, Cushing's disease).

The incidence of muscle weakness ranges from 2 to 20% in persons receiving long-term corticosteroid therapy and from 50 to 80% in those with Cushing's disease.

Critical care quadriparesis is a newly described form of corticosteroid myopathy for which the elderly are at increased risk. It develops acutely, often in a patient with a severe medical disorder that requires large IV doses of corticosteroids, frequently with concomitant use of depolarizing muscle relaxants. Selective dissolution of thick filaments in muscle is characteristic. Recovery often requires many months and is commonly incomplete.

Symptoms, Signs, and Diagnosis

In patients taking long-term systemic corticosteroids and in those with intrinsic cortisol excess (eg, Cushing's disease), muscle weakness usually begins in the hip girdle, especially the quadriceps, and eventually spreads to nearly all muscles. The proximal muscles tend to be most affected; except for the neck flexors, muscles supplied by cranial nerves are spared. Patients often report that they become fatigued more rapidly during activities demanding sudden bursts of power. If the myopathy is long-standing, muscle wasting often becomes apparent, although exercise decreases it. Occasionally, patients experience mild aching in the thigh muscles, but severe pain does not occur. Tendon reflexes remain unchanged, and no fasciculations develop.

A majority of patients have other signs of corticosteroid toxicity (eg, weight gain, cushingoid appearance, hypertension). Typically, serum CK and other muscle enzyme levels, electromyography findings, and nerve conduction studies are normal. Muscle biopsy results often show striking atrophy of type 2 fibers.

Intrinsic cortisol excess can be detected by measurements of plasma cortisol at different times of day. Determination of the underlying cause of the cortisol excess is beyond the scope of this discussion.

Prevention and Treatment

For prevention of iatrogenic disease, switching to alternate-day corticosteroid administration as soon as feasible is often recommended. Maintaining exercise to whatever degree possible is also important.

Treatment of iatrogenic disease is empiric. However, gradually reducing the corticosteroid dosage and closely monitoring the patient are essential. If the weakness is due primarily to an inflammatory myopathy and corticosteroids have slowed but not stopped the progression of weakness, reducing the corticosteroid dose increases creatine excretion and worsens muscle weakness. However, if the weakness is due primarily to corticosteroid therapy, decreasing the corticosteroid dose allows muscle strength to gradually return. Complete recovery usually occurs in 2 to 3 months.

In those in whom the myopathy is due to intrinsic cortisol excess, treatment depends on the underlying cause.