Dirofilaria immitis Causing Flexor Tenosynovitis of the Hand: A Rare Case Report

This case describes a previously underreported case of flexor tenosynovitis. A 23-year-old male slaughterhouse employee presented with several weeks of increased pain and swelling in their left third digit. They failed nonoperative management, including anti-inflammatory medication and oral steroids, followed by corticosteroid injection. Intraoperative pathology demonstrated subacute flexor tenosynovitis due to a rare parasitic infection of Dirofilaria immitis. Dirofilaria immitis, a parasitic roundworm commonly found in dogs, rarely causes zoonotic infections in humans. In cases when this parasite infects humans, it primarily impacts pulmonary, ocular, and subcutaneous tissues. This diagnosis was ultimately only able to be made due to pathologic analysis, as they had negative cultures. This case highlights that tissue pathology is essential in atypical infections, especially culture-negative tenosynovitis.