Rhabdomyolysis

Rhabdomyolysis describes the breakdown of striated muscles with the release of intracellular contents and represents a severe muscle injury. MRI is the imaging modality of choice. Rhabdomyolysis is potentially life-threatening although recovery is excellent with early treatment.

Clinical presentation

Symptoms and signs are varied, but a classic triad of muscle pain, weakness, and dark urine are described. 

Pathology

Aetiology

Most common causes reported in Western adult populations are trauma/crush injury, exercise, cocaine use and immobilisation. TheHowever, the range of causes is wide ^12,13: 

• non-traumatic

  • infectious

    • infectious myositis

    • bacteria (mycoplasma, clostridia, legionella)

    • viruses (enterovirus, influenza, herpes simplex)

  • electrolyte abnormalities

    • hypokalaemia, hypocalcaemia, hypophosphataemia

  • immune-mediated

    • dermatomyositis, polymyositis, immune mediated necrotising myopathy

  • endocrine

    • hyperthyroidism

    • hypothyroidism

  • xenobiotics

    • ethanol, HMG-CoA reductase inhibitors (statins), fibrates

    • amphetamines, cocaine, synthetic cannabinoids

    • carbon monoxide, arthropod¹⁴ and snake venoms

    • Tricholoma equestre (mushroom)

    • antipsychotics, SSRIs, doxylamine

    • adalumimabadalimumab, rituximab

  • extremes of temperature

    • hyperthermia

    • hypothermia

  • inborn errors of metabolism

    • myophosphorylase deficiency

    • fatty acid oxidation disorders

  • limb ischaemia

  • prolonged immobilisation

• traumatic

  • compartment syndrome

  • crush injury

  • electrocution

  • excessive muscle activity

    • generalised tonic-clonic seizures

    • long distance running

    • serotonin toxicity

    • neuroleptic malignant syndrome

    • metabolic myopathy (e.g. carnitine palmitoyltransferase II deficiency)

Markers

• elevated serum creatinine kinase (CK)

  • at least five times upper limit of normal

• hyperkalaemia, hypophosphataemia, hypocalcaemia

• hyperuricaemia, elevated lactate dehydrogenase

• elevated aspartate aminotransferae

• haem positive urine dipstick

  • with an absence of erythrocytes on microscopy

• myoglobinuria, myoglobinemia

Radiographic features

CT

Rhabdomyolysis has a heterogeneously hypodense appearance on CT. There may be rim-enhancement on post-contrast images ^7,8.

MRI

Oedema throughout affected muscles with signal intensity reflecting the severity of an injury is seen in mild-moderate cases. When severe, features of myonecrosis will be demonstrated. Two types of MRI findings have been described ^4,8:

• type 1

  • T1: homogeneously iso to hyperintense

  • T2/STIR: homogeneously hyperintense

  • T1 C+ (Gd): homogeneously enhancing

• type 2

  • T1: homogeneously/heterogeneously hyperintense

  • T2: heterogeneously hyperintense

  • T1 C+ (Gd): rim-enhancing

Ultrasound

Described features include a loss of the organised fascicular sonographic architexturearchitecture characteristic of muscle with hyperechoic and hyperechoic foci ^9,10. The muscle may demonstrate an increase in thickness ¹¹.

Treatment and prognosis

The release of intracellular contents (e.g. myoglobin) can result in the development of cardiac arrhythmias, and acute renal failurekidney injury (~30%) and tetanus. Muscle oedema may lead to compartment syndrome. Full recovery is possible with early treatment. 

Differential diagnosis

For MRI appearances consider:

• differential diagnosis of skeletal muscle oedema on MRI