A 42-year-old overweight immunocompetent woman with a history of hypertension and mild psoriasis and no travel history was seen twice in the emergency department-11 days prior to admission and again 8 days prior to admission-with tachycardia, tachypnea, and left infrascapular back pain that radiated to her chest. Her white blood count was 8.52 K/µL (normal range, 3.7 to 10.4 K/µL), and chest radiograph and computed tomographic (CT) scan were negative for any bony abnormalities or cardiopulmonary pathology. The patient was given muscle relaxants and narcotic medication on both occasions and discharged home.

Five days prior to admission, the patient reported using her arms to help stand up and immediately feeling a "pop" in her shoulder with associated pain. She saw her primary care physician 2 days later for evaluation. Her upper back pain had diminished; however, her shoulder was noted to be erythematous, warm, and diffusely tender to palpation. Range of motion of the shoulder joint was decreased in abduction. A complete blood count revealed leukocytosis at 15 K/µL. The patient was prescribed cefadroxil 1 g twice daily for 10 days of treatment for presumed cellulitis of the shoulder and anterior chest.

The patient again returned to her primary care physician with a fever, increased pain, and decreased range of motion in her shoulder. She had an ultrasound-guided aspiration of the left AC joint, blood cultures were taken, and she was admitted to the hospital. Her admission testing revealed a white blood cell count of 18 K/µL, a platelet count of 660 K/µL (reference range, 140 to 385 K/µL), a C-reactive protein concentration of 9.9 mg/dL (normal range, 11.8 to 15.1 mg/dL), erythrocyte sedimentation rate of 60 mm/hr (normal range, < 25 mm/hr), and blood cultures negative for growth. A CT scan of the patient's shoulder revealed no signs of osteomyelitis. A magnetic resonance imaging (MRI) scan without contrast of the left shoulder revealed increased fluid collection on short TI inversion recovery (STIR) images in the anterior deltoid and supraspinatus, as well as in the AC joint (Fig. 1). No hyperintensity on STIR images was noted in the glenohumeral joint. Cultures from the AC joint revealed a Staphylococcus aureus susceptible to methicillin, but due to a penicillin allergy, she was initially treated with intravenous (IV) vancomycin therapy and later changed, based on susceptibility testing, to 900 mg clindamycin IV 3 times a day while in the hospital.

An open incision and drainage was performed on hospital day 2. A large amount of necrotic tissue and pus was drained from the anterior deltoid and supraspinatus muscles, and a small amount from the AC joint. The clavicle was soft with cystic changes compatible with osteomyelitis, and a small fragment of the distal clavicle was excised.

Immediately after surgery, the patient felt better, had improved shoulder range of motion and decreased erythema, and was discharged on hospital day 5 on 300 mg oral clindamycin 3 times a day for 25 days to complete 5 weeks of antibiotic treatment. On her follow-up appointment 2 weeks after discharge, she was feeling better and had no further signs of infection, and at 5 months had a full range of her shoulder function without signs of recurrent infection.

Over 4 or 5 days prior to her admission to hospital, a 50-year-old woman developed increasing pain erythema, and swelling over the left SC joint. The patient's past medical history was noteworthy for a remote history of IVDA, hypothyroidism, and hypertension. Pertinent findings were pain and swelling over the left SC joint with pain in the left contiguous SCM muscle, but no definite fluctuance. Joint aspiration revealed frank pus, and gram-positive cocci were seen on a Gram stain. On admission the patient had a blood pressure of 132/78 mmHg, pulse of 105 beats per minute, respiration rate of 18 breaths per minute, and temperature of 37.4℃.

Initial laboratory results revealed no evidence of drug abuse on urine testing, a white blood cell count of 16.3 K/µL, 91% polymorphic nuclear cells, and an SC joint aspirate with 140 K/uL white blood cells. Cultures returned S. aureus susceptible to methicillin. The patient's initial antibiotics, IV vancomycin and IV piperacillin tazobactam, were therefore changed to oxacillin 2 g IV every 6 hours. On day 2 of hospitalization the tenseness and swelling over the SC joint worsened, and was incised and drained of purulent material. The next day, with increasing pain and swelling of the SCM muscle, an MR scan revealed fluid collection on STIR images in the SC joint, edema of the proximal bone, and liquefaction of the entire SCM muscle from the SC joint to the base of the skull (Fig. 2). This muscle was, therefore, incised inferiorly, drained of a large amount of purulent material, and was packed with iodoform gauze. Subsequently, the patient has responded to IV antibiotics directed against the S. aureus, first with 2 weeks of oxacillin IV followed by 4 weeks of outpatient ceftriaxone IV 2 g per day. At follow-up, her joint and left neck pain had improved, but atrophy of the SCM muscle was noted. In more than 12 month follow-up, there has been no signs of infection recurrence.