Abstract
Pyogenic myositis is a bacterial infection of skeletal muscle that is usually caused by Staphylococcus aureus and is common in tropical regions. Recently, this infection has also been reported in immunocompromised patients in temperate regions. The lower extremities and trunk are most affected, while involvement of the chest wall is rare. We report a case of pectoralis major pyomyositis caused by Morganella morganii in an 82-year-old Japanese man with type 2 diabetes mellitus who had undergone stenting for myocardial infarction. Four months prior to visiting our hospital, the patient became aware of pain in the right chest area, which gradually became swollen. One month before the visit, the pain and swelling had become more severe. At the visit, there was swelling in the right anterior thoracic region with a diameter of 10 cm and pain in the same region. On physical examination, his blood pressure was 133/64 mmHg, heart rate was 83 beats/min, and body temperature was 36.9℃. Initially, a sarcoma or other neoplastic lesion was suspected and a needle biopsy was performed. Pus was drained from the puncture site to collect wound culture. Needle biopsy of the lesion did not reveal any fungi or acid-fast bacteria, and a T-SPOT.TB test was negative. Computed tomography and magnetic resonance imaging suggested abscess formation under the pectoralis major muscle. A wound culture test detected Morganella morganii, and pectoralis major pyomyositis was diagnosed. Debridement was performed under general anesthesia. The necrotic pectoralis major muscle was excised, the abscess cavity was opened, and wound irrigation was performed. The postoperative course was good and the patient was discharged on the 16th postoperative day. There has been no recurrence in eight months postoperatively. Pectoralis major pyomyositis may not be relieved by antibiotics alone and may extend to deeper organs to form intrapleural abscesses. Therefore, prompt drainage should be performed to prevent serious complications in a case in which abscess formation is observed.