Background Pyomyositis (PM) is an acute pyogenic bacterial infection of skeletal muscle that may arise from haematogenous spread (primary PM) or by contiguity (secondary PM). Although PM is more common in tropical countries, its incidence is increasing in other areas due to the high number of immunocompromised patients, who have a poor prognosis and elevated mortality.
Objectives To describe epidemiological characteristics, clinical spectrum, laboratory and microbiological findings, therapeutic and outcome of patients with PM treated at a Spanish tertiary hospital.
Methods We performed a retrospective study of patients diagnosed with PM admitted to our hospital between January 1991 and October 2014. The data were obtained by reviewing their medical records.
Results A total of 41 cases were included, most of them males (73.1%), with a mean age at diagnosis being 46 years (range: 1-84). The mean time from onset of symptoms to diagnosis was 2.3 weeks (range: 1-16). The most common clinical manifestations were pain (92.5%), fever (72.5%) and local swelling (67.5%). Large muscle groups were more frequently affected, especially lower limbs (70.7%), and 15 patients (36.6%) developed multifocal involvement. Leucocytosis was found in 64.8% and neutrophilia in 72.9%. The mean values of ESR and CRP were 91.5 mm/h and 158.3 mg/dL respectively, and CPK levels were increased in 5/18 cases. Imaging test were performed in 40 patients (ultrasonography 26, CT 29, MRI 8) and demonstrated muscle abscesses in 73.2%. Nine cases (22%) corresponded to secondary PM and the most commonly associated infections were cellulitis, arthritis and osteomyelitis. Underlying diseases most frequently found were HIV-1 infection in 12 cases, chronic C hepatitis in 10 cases (coinfection with HIV-1 in 7) and diabetes mellitus (DM) type 2 in 5 cases (12.2%). There was a previous diagnosis of autoimmune disease (AD) in 14,6% (2 rheumatoid arthritis, 1 lupus/Sjögren overlap, 1 p-ANCA vasculitis,1 Addison's disease and 1 DM type 1) and intravenous drugs abuse in 24.4%. Aspirate of muscle abscesses was performed in 37 cases, being positive for Staphylococcus aureus in 67.5%, Streptococcus sp. in 10.8% and polymicrobial infection in 16.2%. Blood cultures were positive in 17/35 patients and the most frequently isolated pathogen was S. aureus. Information regarding treatment was available in 38 cases, 50% of them receiving combinations of 2 intravenous antibiotics, the most common being cloxacillin + gentamicin, with median treatment duration of 4 weeks (range: 1-19). Drainage was performed in 32/41 (7 percutaneous, 25 surgical). Associated mortality was 19.5%, mainly due to septic shock. The most frequent complications were pneumonia (12.2%), endocarditis (4.9%), septic thrombophlebitis (4.9%) and myonecrosis (4.9%).
Conclusions PM is a serious, potentially life-threatening infection that primarily affects large muscle groups. Most patients have a predisposing factor; the most frequent in our patients were HIV infection, chronic C hepatitis, DM type 2, AD and intravenous drugs abuse. Mortality in our series was higher than reported in previous studies (0.5-10%). A better knowledge of this infection is mandatory for early diagnosis and appropriate treatment.
Disclosure of Interest None declared