Septic arthritis mimic unmasked: inflammatory bowel disease-associated arthritis in a patient with a learning disability.

Arthritis is a recognised extraintestinal manifestation of inflammatory bowel disease and can rarely precede gastrointestinal recognition, mimicking septic arthritis. Communication barriers in patients with learning disabilities may obscure systemic symptoms.A man in his early 30s with a mild learning disability presented with acute left-knee pain, swelling, erythema and fevers with concurrent low-back and hip pain. Arthrocentesis yielded turbid fluid with a white blood cell count (WBC) of 20.4×10⁹/L (93% neutrophils); Gram stain, crystals and cultures (including gonococcal testing) were negative. CT abdomen/pelvis showed mild colonic wall thickening suggestive of colitis. He received empiric antibiotics, but synovial and blood cultures remained negative. A repeat, simplified interview with collateral history uncovered a year of intermittent diarrhoea. Colonoscopy and biopsy findings were compatible with Crohn's disease. Antibiotics were stopped and prednisone plus methotrexate, then infliximab, led to clinical and laboratory improvement with no active bowel inflammation on follow-up MR enterography.