Sternoclavicular joint septic arthritis and osteomyelitis caused by Aggregatibacter aphrophilus

A 62-year-old lady was referred to the Infectious Diseases outpatients clinics with a 3-week history of right shoulder pain and a 1-week history of progressive swelling and erythema of the soft tissue overlying the right sternoclavicular joint (SCJ). No systemic symptoms were reported. No triggering event could be recalled and there was no recent travel, no animal exposure and no known contact with tuberculosis. On examination, temperature was normal and the patient appeared systemically well. There was an indurated, tender, erythematous, warm swelling over her right SCJ with associated decreased range of movement of the right shoulder. Cardiac examination revealed a soft systolic murmur. No other peripheral stigmata of endocarditis were identified. The patient was admitted for investigation and work up of a suspected SCJ septic arthritis arising either as a consequence of an undocumented bacteraemia or due to a contiguous extension from overlying skin and soft tissue infection. Initial laboratory investigations revealed a normal white cell count and differential. Inflammatory markers were elevated with an ESR of 94 mm/h (<36) and a CRP of 84 mg/l (<5). Serial blood cultures were obtained prior to therapy commencement. A targeted ultrasound (US) of the SCJ was performed urgently. This identified a small pocket of fluid adjacent to the right SCJ, intimately associated with the joint space. This fluid was aspirated under US guidance. Treatment comprising high-dose intravenous (IV) flucloxacillin and benzylpenicillin was subsequently commenced. Imaging with computed tomography and magnetic resonance (MR) revealed marked soft tissue oedema surrounding the SCJ associated with oedema and inflammatory changes in the adjacent bone and parietal pleura (Figure 1a and b). A transthoracic echocardiogram did not identify any features suggestive of endocarditis. This finding was later confirmed with a trans-oesophageal echocardiogram. Figure 1. ( a ) Computed tomography image. Marked …