Age / Sex : 44 / M

Age / Sex : 44/M

Chief complaint : Painful swelling and redness, both leg (Rt>Lt)

                            Weakness, Rt leg                  

rhabdomyolysis

Discussion

Findings:

- On ultrasonography, fascicular architecture of adductor muscle is disorganized with small hypopechoic area. There is no thrombosis in deep venous system.

- On T2-weighted MR images, there are bilateral asymmetric high signal intensities in pelvis, thigh, and calf muscles. Gluteus m., adductor m., semimembranous m., vastus lateralis m. soleus m. tibialis anterior m., peroneus m. are involved.

- Some fluid collections in the fascial plane, surrounding biceps femoris and adductor m.

- Subcutaneous fat layer appears to be normal.

- On Gd-enhancement T1-weighted MR images, some muscles are weakly enhanced at its periphery. There is no enhancement of deep fascia. 

Differential Diagnosis:

1)       Necrotizing fascitis

2)       Deep vein thrombosis

3)       Delayed-onset muscle soreness (DOMS)

Diagnosis:  Rhabdomyolysis

Discussion:

Rhabdomyolysis may result from various clinical causes, including overexertion, direct trauma, vessel occlusion, drug overuse, CO intoxication, alcohol abuse. Prompt diagnosis of rhabdomyolysis is important because it can be associated with acute renal failure and compartment syndrome, hypercalemia, and metabolic acidosis.

The most sensitive indicator is elevated serum CK (creatine kinase) level, which peaks in 1-3 days and subsequently declines. Thigh, calf, and back muscles are the common sites of rhabdomyolysis. Affected muscles may be either bilateral and symmetric or unilateral and asymmetric.

On MRI, the affected muscles are homogeneously isointense or hyperintense on T1-weighted images, homogeneously hyperintense on T2-weighted and STIR images, and homogeneously enhanced or rim enhanced on contrast-enhanced MR images. Occasionally, dot-like or linear streaky enhanced foci within an area of rim enhancement in affected muscles on contrast –enhanced images, which is called as “stipple sign”. Subfascial fluid collection and subcutaneous edema may or may not be seen.

On US, acute rhabdomyolysis is depicted as regions of disorganized fascicular architecture with hypoechoic area caused by edema. Sonography can exclude the possibility of deep vein thrombosis in patients with lower extremity pain and swelling.

On CT, the affected muscles are enlarged with sharply marginated low density area. It should be avoided to use of IV contrast agents in patients who are in danger of renal failure from rhabdomyolysis.

References:

1. Lu CH, Tsang YM, Yu CW, Wu MZ, Hsu CY, Shih TT. Rhabdomyolysis: Magnetic Resonance Imaging and Computed Tomography Findings J Comput Assist Tomogr. 2007:31(3):368-374.

2. Boutin RD. Muscle disorder. In: Resnick D. Diagnosis of bone and joint disorders, 4^th ed. Philadelphia: Saunders, 2002:4735-4737