Neonatal Septic Shoulder Joint Masquerading as Brachial Plexus Palsy: A Case Report and Review of the Literature

<b>Case:</b> A 2-week-old girl presented to the hospital with a 1-day history of decreased spontaneous movements of her left arm at the shoulder and elbow. There was no history of trauma, and she was otherwise well. Clinically, there was evidence of a C5/6 palsy. MRI of the left shoulder demonstrated an effusion and synovial thickening at the left glenohumeral joint. She was managed with a surgical washout of the joint and intravenous antibiotics. At a 7-month follow-up, she demonstrated a symmetrical range of movement in both shoulders with no signs of acute or chronic infection on X-ray. <b>Conclusion:</b> Septic arthritis of the glenohumeral joint presents insidiously in neonates and infants without typical signs of infection. Neonates and infants presenting with suspected brachial plexus palsy without a convincing history of trauma should raise suspicion of underlying joint infection and be investigated accordingly with blood tests and a low threshold for imaging of the shoulder to facilitate early diagnosis and management.