A 25–year–old Caucasian man with no past medical history complained of 3 days of severe bilateral “gnawing” pain in his calves and forearms. It began in his right calf, preceded by 2 h of overlying erythema, and spread to his opposite calf and both forearms, in each case preceded by erythema. He recalled several recent episodes of profuse sweating and chills but denied other complaints. He also denied recent muscle trauma, vigorous exercise, alcohol or drug use and was taking no medications. He had been stationed in Haiti and Iraq within the past 18 months while serving in the army. On examination, vital signs were normal. Both calves and forearms were exquisitely tender to palpation and the skin overlying the right forearm was erythematous and warm. Laboratory studies were significant for leukocytosis, mildly elevated erythrocyte sedimentation rate and creatine phosphokinase, and negative blood cultures. Serology for HIV and antinuclear antibody were negative. Lower extremity MRI revealed multifocal microabscesses in both gastrocnemius muscles consistent with pyomyositis (Figure 1). The diagnosis was confirmed by muscle biopsy which showed perimysial and endomysial inflammation with myophagocytosis and myofiber necrosis. Empiric antibiotic therapy was begun and within 2 days the patient was asymptomatic.
Pyomyositis is a purulent infection of skeletal muscle occurring predominantly in tropical areas, often in otherwise healthy individuals. In contrast, rare cases in temperate climates have been associated with previous trauma, infection or immunocompromised state. Muscle groups most commonly affected include quadriceps, gluteal, iliopsoas and abdominal. Multisite involvement is noted in up to 20% of cases but to our knowledge bilateral, multifocal involvement has been reported only once previously in immunocompetent residents of temperate areas. Laboratory findings are typically nonspecific but bacteremia is observed in 10% and 35% of tropical and temperate cases, respectively. MRI is the gold standard for diagnosis as other imaging modalities may reveal only nonspecific changes. Treatment includes surgical drainage of abscesses and at least 2–4 weeks of antibiotics which cover Staphylococcal aureus, responsible for up to 90% of cases with an identifiable pathogen. Mortality is reported to be less than 1% when treatment is initiated early but increases to 15% when delayed; overwhelming sepsis is the most common cause of death.
The differential diagnosis of myalgias includes a variety of conditions that cause symptoms similar to pyomyositis. In the absence of positive blood cultures, laboratory findings are nonspecific. Our patient highlights the importance of obtaining a travel history and an early MRI in the evaluation of unexplained myalgias and severe muscle tenderness. The prompt initiation of antibiotics may be curative in this unfamiliar but potentially fatal disease.
Figure 1T2 weighted MRI revealing multifocal microabscesses (arrows) in the both gastrocnemius muscles.