Case Presentation:

A 45‐year‐old man with history of hepatitis C presented with a 7‐day history of worsening pain in his right arm and chest. His symptoms initially began as a sharp stabbing pain in his right bicep that within 2 days was associated with overlying warmth, swelling, and erythema. The patient was started on oral clindamycin at an outside facility, but after 2 days of worsening pain and swelling, he presented to our emergency department. Initial vital signs were normal; his right arm had a large area of purplish discoloration with associated edema and heat that extended from the right bicep to the chest. Laboratory studies were notable only for slight leukocytosis (12.4 g/dL). The patient was started on IV vancomycin. Over the next 48 hours his pain and swelling continued to worsen despite negative blood cultures and a vancomycin trough within therapeutic range. The erythematous area had developed areas of “woody” induration, and his white blood cell count increased to 19.2 g/dL CT scan with IV contrast revealed 2 large rim‐enhancing lesions within the pectoralis major and triceps brachii muscles. The patient was taken to the operating room where >150 cc of purulent fluid was evacuated through 3 separate incisions. Subsequent wound cultures grew out methicillin‐resistant Staphyloccous aureus. Following 2 additional days of IV vancomycin the patient was transitioned to a 4‐week course of oral trimethoprim‐sulfamethoxazole. Five weeks later his symptoms had resolved without recurrence.

Discussion:

Pyomyositis is an acute, destructive bacterial infection of skeletal muscle clinically manifested by severe muscle pain. During initial stages, inflammation is concealed beneath tissue fascia limiting skin involvement. As the infection progresses, overlying skin may appear warm, swollen, and erythematous, similar to cellulitis. Despite its rare occurrence, pyomyositis cannot be overlooked; failure to promptly initiate therapy can lead to serious complications including septic shock, rhabdomyolysis, and, in 10% of cases, death. Laboratory values are often nonspecific and blood cultures are often negative. Clinical clues suggesting pyomyositis include immunocompromising conditions, recent travel to tropical regions, skin changes with “woody” induration, and failure to improve with antibiotics. An additional hallmark is the occurrence of pain preceding skin changes due to spread from the “inside‐out” as opposed to the “outside‐in” spread in cellulitis. If suspected, CT scan with IV contrast should be utilized to identify areas of image attenuation (due to an accumulation of fluid) with rim enhancement. Immediate treatment should be initiated with intravenous antibiotics and percutaneous or surgical (with extensive infection) drainage.

Conclusions:

Pyomyositis should be suspected in apparent soft‐tissue infections in which pain precedes skin changes. If suspected, CT scan with IV contrast should be utilized to allow for initiation of antibiotics and drainage.