Pyomyositis--with special reference to the comparison between extra- and intrapelvic muscle abscess.

Fifteen patients, nine males and six females, diagnosed with pyomyositis from 1988 to 1994, and followed for an average of 69.8 months, were reviewed. Excluding two children, the average age was 56.6 years. Eleven adults (73.3%) had underlying diseases. The lesions were multiple in five patients (33.3%) and a total of twenty-four muscle abscesses, including eleven extrapelvic and thirteen intrapelvic, were identified. When comparing extra- and intrapelvic pyomyositis, intrapelvic pyomyositis presents a diagnostic challenge requiring a high index of suspicion. Distinct clinical features such as local heat and painful swelling were all identified in extrapelvic pyomyositis, but they rarely (in only two of the thirteen lesions) emerged in intrapelvic pyomyositis. The average time from presentation to diagnosis was significantly longer in intrapelvic than in extrapelvic pyomyositis (1.4 vs 9.7 days). Although aspiration showed a high diagnostic rate in extrapelvic muscle abscesses, it was difficult to perform and was occasionally misinterpreted in intrapelvic cases. Routine X-rays were not helpful in making the diagnosis. CT scan was valuable because it provided positive diagnostic findings in all twelve patients who received one. The causative organisms in our patients were Staphylococcus aureus in eight (53.3%), Escherichia coli in three (20%), and Klebsiella in three (20%). Treatments consisted of parenteral antibiotics for all patients, image-guided aspiration in four patients, and surgical drainage in eleven patients. Two intrapelvic pyomyositis patients expired due to sepsis. At the completion of the study, twelve patients were asymptomatic without sequel, and one patient had a recurrence.