Abstract
Reactive arthritis (ReA) is a syndrome of arthritis and tenosynovitis with defined extra-articular manifestations following certain infections. Despite being recognized a long time ago, debates still surrounds its definition. It is still unclear if the spectrum of the disease should include arthritis induced by other than the classical organisms. Here, we present an unusual cause of ReA. A young healthy female patient presented with acute polyarthritis and acute urticaria after 2 weeks of diarrheal illness. She was found to have blastocystis in the stool microscopy. Extensive evaluation ruled out other causes of her arthritis. She received metronidazole with a short course of NSAIDS and steroids with complete resolution of her skin and joint symptoms. She was followed for six months with no recurrence of arthritis or urticaria. Blastocystis sp. is a parasite that is prevalent in developing countries. It has been linked to isolated ReA or isolated urticaria among a few other case reports. This is the very first case to have blastocystis induced ReA that coexisted with acute urticaria. Upon review of the literature, we found that blastocystis induced ReA affects mainly young and middle-aged females such as in our case. The arthritis is usually settled with the parasite eradication. Finally, urticaria might be a distinguishing feature for blastocystis induced ReA that requires specific antimicrobial therapy.