A 56-year-old woman presented to hospital with progressively worsening left upper quadrant and flank pain, which had persisted following a mechanical rotational injury to the thoracic spine sustained four weeks prior. This was initially diagnosed as musculoskeletal pain secondary to injury by her general practitioner, however her symptoms continued to worsen despite resting and avoiding further mechanical aggravation.

Her medical history was significant for seronegative rheumatoid arthritis, for which she took leflunomide 10 mg daily and methotrexate 20 mg weekly with folic acid supplementation for the last two years, and prednisolone at a stable dose 2.5 mg daily. She had also been commenced on subcutaneous tocilizumab 162 mg weekly, three months prior by her rheumatologist.

She also had a recurrent Bartholin cyst infection for the preceding six weeks, from which microbiological swab samples taken had cultured methicillin-sensitive Staphylococcus aureus (MSSA). This had been managed by her general practitioner with short courses of amoxicillin-clavulanic acid – including most recently a five-day course, completed two weeks prior to presentation. Her immunosuppressive therapy was withheld for the preceding two weeks but she continued low dose prednisolone.

She did not report any adverse reaction to amoxicillin-clavulanic acid and had also tolerated this previously for other indications. She did not have any known allergies. She did not start any new herbal or over the counter medications, or prescribed medications, except for tocilizumab.

She did not have any urinary symptoms, other infective symptoms, nor a history of renal stones or gallstones. She did not have any prior history of immunodeficiency, hyposplenism, diabetes mellitus, endocarditis or other recent systemic infection. She did not have any history of intravenous drug use, excessive alcohol use, prostheses or implants. She did not have any significant or severe infections in the preceding two years while taking methotrexate and leflunomide.

On examination, she was febrile but haemodynamically stable. She had left upper quadrant abdominal tenderness and guarding on palpation, and reduced breath sounds with dullness on percussion over the left lung base. She did not have any new rashes, arthralgia or active tenosynovitis. Blood investigations revealed elevated inflammatory markers with a CRP of 286.2 mg/L and neutrophilia of 10.17 x 10⁹/L. Her renal function was normal with no electrolyte derangement. Her liver function tests were unremarkable.

Computerised Tomography (CT) of the abdomen revealed findings concerning for a subcapsular splenic abscess and a left-sided empyema (Figure 1). These findings were new compared to a CT performed four weeks prior at the time of the original injury.

Splenic abscess drainage was performed under ultrasound guidance, revealing frank pus with heavy growth of MSSA. Video assisted thoracoscopy (VATS) and washout of the left-sided empyema and pleural effusion was performed, with MSSA again isolated on two pleural biopsy specimens. Blood cultures were negative for any growth. A transthoracic echocardiogram was normal with no evidence of vegetations or valvular abnormalities. A nuclear medicine bone scan did not demonstrate any evidence of focal osteomyelitis.