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# 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.

Updated Nov 12, 2026

## Key points

- Statin myopathy: risk rises with high doses and CYP3A4 inhibitors (clarithromycin, azoles), fibrates; CK and myoglobinuria in rhabdomyolysis.
- Glucocorticoid myopathy: proximal weakness, normal CK, type II atrophy.
- Hypothyroidism: cramps, slow reflexes, raised CK; hyperthyroidism: proximal weakness, normal CK, thyrotoxic periodic paralysis.
- Hydroxychloroquine: vacuolar myopathy with curvilinear bodies and cardiomyopathy.
- Critical illness myopathy: selective loss of myosin filaments, failure to wean from the ventilator; often with critical illness polyneuropathy.
- Rhabdomyolysis: muscle necrosis releasing myoglobin, potassium and CK; acute kidney injury, hyperkalaemia, compartment syndrome.

## 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.

## Memory aid

Steroids spare the CK; statins and spirits spill it; the thyroid weakens the hips either way.

## 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.

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## Elsewhere in DurgiPedia

- [Creatine, phosphocreatine and creatinine](https://durgical.com/en/biochemistry/topics/creatine-phosphocreatine-and-creatinine/)

## Connections

## Related 6

- [Injury by therapeutic drugs: the classic examples](https://durgical.com/en/general-pathology/injury-by-therapeutic-drugs-the-classic-examples/)
- [Necrotizing myopathy, inclusion body myositis and polymyositis](https://durgical.com/en/general-pathology/necrotizing-myopathy-inclusion-body-myositis-and-polymyositis/)
- [Muscle channelopathies and periodic paralysis](https://durgical.com/en/general-pathology/muscle-channelopathies-and-periodic-paralysis/)
- [Cushing syndrome: causes and the adrenals](https://durgical.com/en/general-pathology/cushing-syndrome-causes-and-the-adrenals/)
- [Graves disease](https://durgical.com/en/general-pathology/graves-disease/)
- [Acute tubular injury (acute tubular necrosis)](https://durgical.com/en/general-pathology/acute-tubular-injury/)

## Related conditions 6

- [Rhabdomyolysis](https://durgical.com/en/conditions/rhabdomyolysis/)
- [Critical illness polyneuropathy and myopathy (ICU-acquired weakness)](https://durgical.com/en/conditions/critical-illness-polyneuropathy-and-myopathy/)
- [Cushing syndrome](https://durgical.com/en/conditions/cushing-syndrome/)
- [Hypothyroidism](https://durgical.com/en/conditions/hypothyroidism/)
- [Graves disease (hyperthyroidism)](https://durgical.com/en/conditions/graves-disease/)
- [Alcohol use disorder](https://durgical.com/en/conditions/alcohol-use-disorder/)

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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](https://medlineplus.gov/ency/article/000473.htm) (MedlinePlus, US National Library of Medicine, 2025); [Myositis | Polymyositis | Dermatomyositis | MedlinePlus](https://medlineplus.gov/myositis.html) (MedlinePlus, US National Library of Medicine, 2025).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/toxic-and-endocrine-myopathies-and-rhabdomyolysis/