[A case report of pyomyositis--early diagnosis and follow-up by MRI]

We report a rare case of pyomyositis in a 28-year-old Japanese woman who was not immunocompromised. She was admitted because of high fever, sore throat, and severe tenderness and swelling of the right calf. Redness, swelling, and tenderness indicated presence of acute inflammation in the calf. CT of the lower extremities demonstrated low density areas in the right soleus muscle and surrounding fascia with marked swelling, which were of high signal on T2 weighted images of MRI. There was no finding of abscess formation. A tentative clinical diagnosis of acute pyomyositis was made, and antibiotics therapy with a combination of fosfomycin and sulbactam/cefoperazone was started although the arterial blood culture was negative for bacteria. Associated acute tonsilitis was the most probable focus of pyomyositis. Antibiotics relieved her symptoms, and the inflammation subsided in several weeks. No surgical procedure was necessary. MRI taken tree weeks after the onset demonstrated abscess formation between the soleus and gastrocnemius muscles. Slight high intensity indicating scar formation remained in the area of the former abscess six weeks after the onset. MRI was very useful not only in making the early diagnosis but also in the follow-up of pyomyositis.