Rhabdomyolysis

Rhabdomyolysis describes the breakdown of striated muscles with 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 tried of muscle pain, weakness, and dark urine are described. 

Pathology

Aetiology

• non-traumatic
  • infection, e.g. infectious myositis
  • electrolyte abnormalities, e.g. hypokalaemia, hypocalcaemia
  • immune-mediate, e.g. dermatomyositis, polymyositis
  • drugs, e.g. alcohol, cocaine, statins, anasethetic agents, heparin
  • hyperthermia/hypothermia
  • metabolic disease, e.g. myophosphorylase deficiency
  • ischaemia
  • immobilisation
• traumatic
  • crush injury
  • electrocution
  • excessive muscle activity, e.g. overexercise, severe forms of delayed onset muscle soreness (DOMS)

Markers

• serum creatinine kinase (CK) will be markedly raised (at least five times normal)
• elevated serum potassium
• positive urine myoglobin

Radiographic features

MRI

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

• type 1
  • T1: homogeneously iso to hyperintense
  • T2/STIR: homogeneously hyperintense
  • Gad C+: homogeneously enhancing
• type 2:
  • T1: homogeneously/heterogeneously hyperintense
  • T2: heterogeneously hyperintense
  • Gad C+: rim-enhancing

Treatment and prognosis

Release of intracellular contents (e.g. myoglobin) can result in the development of cardiac arrhythmias, acute renal failure (~30%) and tetanus. Muscle oedema can result in compartment syndrome. Full recovery with early treatment.