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.
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Clinical presentation
Symptoms and signs are varied, but a classic triad of muscle pain, weakness, and dark urine are described.
Pathology
Etiology
Most common causes reported in Western adult populations are trauma/crush injury, exercise, cocaine and immobilization. The range of causes is wide:
- non-traumatic
- infection, e.g. infectious myositis
- electrolyte abnormalities, e.g. hypokalemia, hypocalcemia
- immune-mediated, e.g. dermatomyositis, polymyositis
- drugs, e.g. alcohol, cocaine, statins, anesthetic agents, heparin
- hyperthermia/hypothermia
- metabolic disease, e.g. myophosphorylase deficiency
- ischemia
- immobilization
- traumatic
- crush injury
- electrocution
- excessive muscle activity, e.g. over exercise, 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
CT
Rhabdomyolysis has a heterogeneously hypodense appearance on CT. There may be rim-enhancement on post-contrast images 7,8.
MRI
Edema 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
Treatment and prognosis
The release of intracellular contents (e.g. myoglobin) can result in the development of cardiac arrhythmias, acute renal failure (~30%) and tetanus. Muscle edema may lead to compartment syndrome. Full recovery with early treatment.
Differential diagnosis
For MRI appearances consider:
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