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.