[A case of descending necrotizing mediastinitis caused by infection with Streptococcus agalactiae in a patient with diabetes mellitus].

We report a case with an atypical presentation of descending necrotizing mediastinitis (DNM). A 47-year-old woman with a medical history of untreated type 2 diabetes mellitus and influenza type A virus infection 2 weeks prior to admission was referred to our hospital complaining of right cervical pain and right upper limb swelling. A chest enhanced computed tomographic (CT) scan showed a ring-enhanced mass-like shadow extending from the right sternomastoid muscle down to the right upper mediastinum, compressing the right subclavicular vein. We diagnosed the patient as having DNM based on a physical examination and the CT findings. Because the abscess extended from deep in the neck to the upper mediastinum and right upper pleural space, emergent abscess debridement and drainage was required. After hospitalization, antibiotics (Ampicillin/Sulbactam 12 g/day) were also administered based on Gram-stain findings from the drainage fluid, which showed Gram-positive cocci resembling a string of beads. A culture of the drainage fluid identified Streptococcus agalactiae. Aggressive abscess drainage and early antibiotic therapy resulted in a favorable response. She was discharged without complications on the 33rd hospital day. DNM is well known as a rare but lethal disease. In this case, the presence of diabetes mellitus and post-influenza infection might have been risk factors for a serious S. agalactiae infection. Early aggressive therapy and adequate drainage are recommended for patients with DNM.