Toxic and endocrine myopathies and rhabdomyolysis
- Lesion
Drugs, alcohol, hormone imbalance and severe illness can weaken or destroy muscle; the worst case is rhabdomyolysis, which can stop the kidneys.
What it is
Muscle is sensitive to many drugs and metabolic changes. Statins cause myalgia and, rarely, necrotizing myopathy and rhabdomyolysis, more often with interacting drugs. Glucocorticoids cause painless proximal weakness with type II fibre atrophy. Acute alcohol binges cause rhabdomyolysis; chronic use causes atrophy. Hydroxychloroquine and chloroquine cause vacuolar myopathy, colchicine an autophagic vacuolar myopathy with neuropathy, and zidovudine a mitochondrial myopathy. Hyperthyroidism and hypothyroidism both cause proximal myopathy. Critically ill patients, especially with sepsis, steroids and neuromuscular blockers, develop critical illness myopathy with loss of myosin thick filaments.
Structure
- Statin and alcohol rhabdomyolysis: widespread necrotic fibres with myophagocytosis and regeneration.
- Glucocorticoid: selective atrophy of type II fibres without necrosis.
- Antimalarial and colchicine: vacuoles with curvilinear and myeloid bodies on electron microscopy.
- Critical illness myopathy: fibres with loss of ATPase staining from missing myosin, scattered necrosis.
- Zidovudine: ragged red fibres from mitochondrial DNA depletion.
Step by step
- Drugs or toxins impair energy production, membrane integrity or protein turnover in muscle fibres.
- Fibres lose ATP; ion pumps fail and calcium floods the cytoplasm.
- Calcium activates proteases and phospholipases and the fibre necroses.
- Myoglobin, potassium, phosphate, urate and CK pour into the blood.
- Myoglobin precipitates in renal tubules, especially with acidic urine and low volume: acute tubular injury.
Clinical notes
- Rhabdomyolysis triggers: crush injury, prolonged immobilization, extreme exercise, heat stroke, seizures, alcohol, cocaine, statins and inherited metabolic myopathies.
- Dark urine positive for blood on dipstick but without red cells under the microscope suggests myoglobinuria.
- Aggressive intravenous fluids prevent kidney injury.
Test yourself
Think of the answer, then tap the question to see it.
Which fibre type atrophies in glucocorticoid myopathy?
Type II fibres.
Why does rhabdomyolysis cause acute kidney injury?
Myoglobin precipitates in tubules and is toxic to tubular cells, especially with low urine flow and acidic urine.
Which drugs raise the risk of statin myopathy?
CYP3A4 inhibitors such as clarithromycin and azoles, and fibrates, among others.
What is lost from fibres in critical illness myopathy?
Myosin thick filaments.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Rhabdomyolysis: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Myositis | Polymyositis | Dermatomyositis | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.