Skeletal Radiol (1992) 21 : 107-109 Skeletal Radiology Ultrasound in tropical pyomyositis Luca Belli, M.D. 1, Alberto Reggiori, M.D. 2, Eugenio Cocozza, M.D. 2 and Luciano Riboldi, M.D. 1 1 Department of Radiology, Regional Hospital, Varese, Italy; 2 Cooperation Project, AVSI Team, Hoima Hospital, Uganda Abstract. Tropical pyomyositis is an infection of muscles mainly presenting in black people, occurring in the trunk and limbs. At Hoima Hospital, Uganda, 58 patients (30 men and 28 women) with a mean age of 21 years have been investigated by ultrasound; a total of 81 lesions were present. Two different characteristic images were found; abscess was present in 65 cases while 16 patients showed a diffuse infiltration among the muscular fibers. These two different images correspond to the two stages of histologic and clinical progression described by other authors. Ultrasound is useful to demonstrate the pro- gression of pyomyositis and to determine when and where to drain any abscess. Key words: Tropical pyomyositis Abscess- Ultrasound Pyomyositis is a common suppurative infection of striat- ed muscles in tropical areas [1, 2, 7] ; black people, young adults and children of either sex are mainly affected. Single or multiple lesions can be present; the trunk and limbs are especially affected [2, 5]. A discrete invasive lesion of the muscle is the first sign of the disease; an abscess quickly develops in a few days with pain, swelling, and fever. General debilita- tion, vitamin lack, trauma, and parasites have been sug- gested as possible causative cofactors. Usually Staphylo- coccus aureus is present upon culture. Surgical excision plus antibiotics is the treatment of choice. Patients and methods Between July 1989 and July 1990 at Hoima Hospital, Uganda, 58 black patients, 30 men and 28 women, suffering from pyo- myositis were submitted to ultrasound investigation using a linear array scanner (Toshiba SAL-20) equipped with a small parts probe Address reprint requests to: Luca Belli, M.D., Department of Radi- ology, Ospedale Multizonale, Viale Borri n. 57, 1-21100 Varese, Italy (5 MHz). Patients ranged in age from 4 to 65 years (mean 21 years). Results A total of 81 lesions were investigated with ultrasound. In 42 cases the lesions were located on the trunk (chest and abdomen), 41 were in the proximal limbs (shoulder, groin, and buttock), while 25 lesions were equally di- vided between the upper and lower limbs (Fig. 1). Two distinctive and complementary echographic pat- terns were observed (Fig. 2). In 65 cases a fluid abscess inside the muscle was detected; the collection was always hypoechoic and could reach the muscular fascia. Thin septa were sometimes identified. In 16 cases no clear evidence of an abscess was visible, but muscular fibers were widely displaced and infiltrated by a moderate quantity of fluid distributed in the inter- stitial tissue between the fibers following the major axis of the muscle. In this interstitial pattern, the fibers them- selves appeared slightly hypoechoic, probably due to edema. Multiple lesions were present in 18 patients. The disease was always confined within muscle with- out involvement of surrounding structures or the perifas- cial connective tissue. Each patient showed a rapid progress towards abscess formation; many patients attended a few days after the beginning of the symptoms. All were treated with antibi- otics. Excision with surgical drainage was performed in 74 cases. Our hospital had no microbiological laboratory facili- ties and correct identification of the microorganism was not possible. However, in all cases submitted to surgical excision, pus was found in varying quantities. Discussion Scriba (1885) and, soon after, Zeiman (1904) in New Guinea were the first authors to report on pyomyositis 9 1992 International Skeletal Society