Pseudomonas sternoclavicular pyarthrosis. 
Most cases of Pseudomonas pyarthrosis affecting the sternoclavicular joint have been reported in immunosuppressed intravenous drug users.  We report a case of Pseudomonas pyarthrosis in a man who was otherwise immunocompetent, except for his age.  A 66-year-old white man presented to the clinic with a 1-month history of right-sided shoulder and arm pain associated with swelling of the upper part of the chest in the region of the right sternoclavicular joint.  The chest radiograph revealed opacity in the right superior mediastinum.  Computed tomography scan of the chest confirmed a mass in the right sternoclavicular region with associated osteolysis of the clavicular head.  A needle biopsy of the mass was negative for malignancy.  An open biopsy specimen showed evidence of chronic inflammation without evidence of malignancy, and culture of the tissue grew Pseudomonas aeruginosa.  The patient's symptoms improved after extensive incision and drainage of the affected area followed by treatment with antibiotics for 6 weeks.