Introduction
The sternoclavicular joint (SCJ) is a rather atypical site of septic arthritis (SA), comprising less than 1% of SA cases. The most frequently involved bacterium is Staphylococcus aureus, with Pseudomonas aeruginosa coming second in order of frequency (1). It usually develops in patients with a history of intravenous drug use or diabetes mellitus (1,2). A few cases have also been diagnosed on patients with an already compromised joint, such in the case of rheumatoid arthritis (3). Nonetheless, up until now, there has been no description of SCJ SA as a late complication of a pericardiostomy procedure.
Case Report
A 23 years old African Brazilian woman presented with a two-month history of right shoulder pain. She reported a weight loss of 3 kg during this period, but denied fever or other constitutional symptoms. On physical examination, mild wasting of the right deltoid muscle was noticed, attributed to underuse, but the shoulder examination was otherwise unremarkable.
The patient had been diagnosed with systemic lupus erythematosus (SLE) eight months earlier. At the time of diagnosis, she presented with nephrotic syndrome, and a large pericardial effusion requiring pericardiostomy. Pericardial fluid cultures were negative, and the effusion abated after starting of pulse therapy with methylprednisolone and cyclophosphamide.
Four months later, she developed a soft tissue abscess on the previous site of the pericardiostomy. Culture of the abscess yielded P. aeruginosa. She was treated with a 10-day course of cefepime, with complete resolution of the skin infection.
On the current admission, she presented with a c-reactive protein of 47.2 mg/L, an erythrocyte sedimentation rate of 134 mm/1st hour, and a mild leukocytosis of 11,060/mm³, with no left shift. Shoulder magnetic resonance imaging (MRI) did not show any abnormality, neither did chest computed tomography (CT).
Neuralgic amyotrophy of the shoulder (Parsonage-Turner syndrome) was suspected, but an MRI of the right brachial plexus and electroneuromyography did not confirm our hypothesis, though. Surprisingly, though, the MRI showed evidence of synovitis on the right SCJ (Figure 1A).
In the face of these controverted findings, whole body 18fluorodeoxyglucose-positron emission tomography was requested. The PET/CT scan evidenced marked focal hypercaptation measuring 2.8x2.0x3.7 cm on the right SCJ (SUVmax of 9.6), with bone erosion and central necrosis on the lateral border of the manubrium (Figure 1B).
CT-guided biopsy of the bone and aspiration of the synovial fluid yielded a P. aeruginosa with the same antibiotic sensitivity profile as the one cultured from the skin abscess. The patient was started on gentamicin and evolved with substantial improvement of the pain and decrease in inflammatory markers.
Discussion
The SA of SCJ is a very uncommon entity. It usually affects males in the fifth decade of life, with predominance for right-sidedness (1). Risk factors include diabetes mellitus, intravenous drug use, alcoholism, hemodialysis, and human immunodeficiency virus infection (4,5). Nevertheless, no predisposing factor is identifiable in up to a quarter of patients (1,3).
The main manifestation is chest pain, present in up to 80% of cases, although referred shoulder and neck pain may also occur. Effusion is not a prominent feature since the SCJ capsule is not easily distensible. Due to delay in diagnosis, over half of the cases already present with concomitant sternal osteomyelitis (1,2).
Conclusion
Our case highlights that, when evaluating a patient with shoulder pain, besides a thorough examination of the glenohumeral joint, it is important to consider non-articular causes of pain, such as neurologic compromise, as in Parsonage-Turner syndrome, and causes of referred pain, including conditions of the homolateral SCJ.
Ethics
Informed Consent: Consent form was filled out by all participants.
Peer-review: Externally peer-reviewed.
Authorship Contributions
Concept - Design - Data Collection or Processing - Analysis or Interpretation - Literature Search - Writing: M.B.M., R.M.R.P.
Conflict of Interest: No conflict of interest was declared by the authors.
Financial Disclosure: The authors declared that this study received no financial support.