BACKGROUND: An evaluation of the clinical characteristics and profitability of the diagnostic methods of myositis by Staphylococcus aureus was undertaken in favor of earlier diagnosis and treatment. METHODS: Twenty-eight cases of pyomyositis by S. aureus attended over the last nine years were studied. Inclusion criteria were: 1) compatible clinical manifestations, 2) demostration of an abscess in CT and/or surgery, 3) isolation of S. aureus in abscess, hemoculture and/or neighboring tissue. RESULTS: Age: 36 +/- 18 years (limits 9-70). Sex: 23 males (82 %). Neighboring pathology existed in 11 cases (39 %). 5 sacroiliitis (18 %), 4 spondyliodiscitis, 2 osteomyelitis. Favoring/predisposing factors: intravenous drug addiction in 11, staphylococcal sepsis in 6, diabetes mellitus in 4, previous surgery in 3, penetrating muscle injury in 3, and paremetritis in 1. Fourteen cases (50 %) corresponded to primary pyomyositis. The muscle most frequently involved was the psoas/iliacpsoas, followed by near the forearm muscle, spinal, gluteal, and upper pectoral muscles. In 16 cases (57 only one muscle was involved, in 10 two muscles, and in 2 three groups. The time of clinical manifestation prior to consultation oscilated between 1.5-30 days, being less in cases of primary Pyomyositis (p < 0.0005). All the patients referred fever and local pain, with functional impotence in 26 (93 %), general involvement, shivering and perspiration in 24 (86 %). All the patients presented pain upon palpation. In 19 (68 %) there was an increase in local temperature and in 18 a palpable mass. S. aureus was isolated in 16 hemocultures (sensitivity 57 %), in 12 of 13 cultures of neighboring tissue (92 %) and in all those aspirated from abscesses (100 %). CT demonstrated muscular (thickening and/or destructuration or abscess) and neighboring pathology (if existent) in all cases. All the patients received medical treatment. Evacuating puncture was carried out in 7 cases, and surgical drainage in 23 (82 %). Two cases were cured exclusively with medical treatment. Complications were seen in 8 cases (29 %) and two patients died of staphylococcal sepsis. CONCLUSIONS: 1) In myositis by Staphylococcus aureus the percentage of primary pyomyositis is considerable. 2) In secondary pyomyositis the most frequent neighboring processes were sacroiliitis and spondylitis. 3) intravenous drug addiction was the most frequent predisposing factor. 4) The time of clinical evolution is variable although less in case of primary pyomyositis. 5) The performance of hemocultures was found to be greater than described and even greater in primary pyomyositis. 6) Abscess cultures and CT are the most efficient microbiological and imaging techniques in the early diagnosis of myositis by S. aureus.
