Age / Sex : 27 / M

Chief complaint : Lower back pain

What is your impression?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy : Hyun-joo Kim, Soonchunhyang University Seoul Hospital

Discussion

Answer:  Rhabdomyolysis

Myoglobin : >3000 ng/mL, CK : 43846 U/L

Dead lift exercise for 5 days

Findings: 

 Bilateral erector spinae and transversospinalis muscles at the lumbar spine level show heterogeneously high signal intensity on axial T1WI and T2WIs.

Axial and coronal fat-suppressed, contrast enhanced T1WIs show heterogenous enhancement of bilateral erector spinae and transversospinalis muscles at the lumbar spine level.

There is swelling and enhancement in adjacent subcutaneous fat layer, lumbar spine level.

Differential Diagnosis:

 Myonecrosis, Myositis, subacute denervation, delayed onset muscle soreness (DOMS)

Discussion:

 Rhabdomyolysis is a potentially life-threatening disease, which may result from a large variety of causes, congenital or acquired. The acquired causes are toxic, excessive muscle exercise, direct muscle injury, ischemic injury, metabolic disorders, infections, heat stroke, inflammatory myopathies and others. Excessive exercise and heat stroke are probably the most common causes of severe rhabdomyolysis, and it usually occurs in untrained people undertaking vigorous exercise in hot, humid weather.

 Radiological techniques are important for the localization of the affected muscles and their differentiation from the unaffected muscles.

 The ultrasound findings are variable: hypoechoic areas attributed to inflammation and fluid within and surrounding necrotic muscles or hyperechoic regions and locally disorganized fascicular architecture.

CT findings in acute myonecrosis include diffuse areas of low attenuation in the muscle and muscular swelling due to edema and more sharply defined intramuscular hypodense foci corresponding to areas of necrotic muscle. Fatty degeneration and abnormal patchy hyperdensity consistent with muscle calcification, correlated with previous hypocalcemia and with kidney failure (it seems to develop during the subacute stage) is also described. Intravenous contrast material provides better demarcation of the lesions and confirms the avascularity of the necrotic areas.

The sensitivity of MRI detecting abnormal muscles is higher than CT or ultrasound. The affected muscles show an increased signal intensity on T2-weighted spin echo images and decreased signal intensity on T1-weighted images. STIR images display good contrast between normal and abnormal muscles and better differentiation of the damaged muscles from the adjacent fat due to its fat suppression. In the acute stage, the abnormal signal is associated with an increase in the cross-sectional diameter of the affected muscle.

References:

1. European Journal of Radiology 65 (2008) 311–315 ; Importance of MRI in the diagnosis and treatment of rhabdomyolysis


2. AJR 2009; 192:1708–1716; MRI Findings in Inflammatory Muscle Diseases and Their Noninflammatory Mimics


3. RadioGraphics 2000; 20:S295–S315 ; Abnormal Signal Intensity in Skeletal Muscle at MR Imaging: Patterns, Pearls, and Pitfalls