Excerpt from Corticosteroid-Induced Myopathy

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Background

Steroid myopathy is usually an insidious disease process, which causes weakness mainly to the proximal muscles of the upper and lower limbs and neck flexors. Cushing originally described it in 1932. Muller and Kugelberg first studied it systemically in 1959. An excess of either endogenous or exogenous corticosteroids is believed to cause the condition. Excess endogenous corticosteroid production can arise from adrenal tumors. Excess exogenous corticosteroid production can result from steroid treatment for asthma, chronic obstructive pulmonary disease, and inflammatory processes, such as polymyositis, connective tissue disorders, and rheumatoid arthritis.

Pathophysiology

Steroid myopathy may be more frequent with the use of fluorinated steroids, such as dexamethasone or triamcinolone, than with nonfluorinated ones, such as prednisone or hydrocortisone. The exact mechanism of the muscle pathology is unclear but may be related to decreased protein synthesis, increased protein degradation, alterations in carbohydrate metabolism, mitochondrial alterations, electrolyte disturbances, and/or decreased sarcolemmal excitability. Sedentary lifestyle may increase the risk of muscle weakness in a patient taking corticosteroids, since corticosteroids seem to affect less active muscles preferentially. Two distinct types of steroid myopathy exist, acute and chronic. The chronic (or classic) form occurs after prolonged use of corticosteroids and has a more insidious course. The acute form is less common, is associated with rhabdomyolysis, and occurs abruptly while the patient is receiving high-dose corticosteroids.

Frequency

United States

The exact incidence of steroid myopathy is unknown, with each person having different sensitivities to the particular medication used.

Mortality/Morbidity

The weakness seen with steroid myopathy typically resolves after the corticosteroid dose is reduced or discontinued, although it can take weeks to months for recovery. Case studies have reported lack of full recovery and difficulty weaning patients off mechanical ventilation. Osteoporosis, which can be due to the corticosteroid or decreased mobility and respiratory impairment, is a comorbidity that can be seen with steroid myopathy. Other comorbidities, which could occur in any condition causing weakness and immobility, include joint contractures, pressure ulcers, and deep vein thrombi. Mortality has not been described. Although some case studies reported some patient mortalities, there was no indication that steroid myopathy was the cause.

Sex

Women appear to be twice as likely as men to develop muscle weakness for a given dose of steroid, although the reason is unclear.

Please click here to view the full topic text: Corticosteroid-Induced Myopathy