Systemic Mastocytosis: A Mimicker of Reactive Arthritis

OBJECTIVES: Illustration of a case of systemic mastocytosis mimicking reactive arthritis in the absence of an infectious etiology. METHODS: Review of the patient's medical records. RESULTS: We report a case of systemic mastocytosis relapse, presenting with pancytopenia accompanied by knee monoarthritis, cystitis, and bilateral conjunctivitis occurring simultaneously at the same time interval within 2–4 days, mimicking reactive arthritis in the absence of an infectious etiology. CONCLUSION: Our case demonstrated reactive arthritis features (triad of urethritis, conjunctivitis, and arthritis) without an infectious trigger but rather a relapse of mastocytosis. We should think outside the box when faced with such a clinical scenario in the absence of an infectious etiology. Paraneoplastic reactive arthritis is to be considered after excluding an underlying infection.