CME Rheumatology 20: Parvovirus B19-Induced Tenosynovitis? Abstract. In this case presentation we discuss diagnostic algorithms and differential diagnoses in undifferentiated tenosynovitis. We present a case of a patient with chronic tenosynovitis in the 4th extensor tendon compartment. With unremarkable anamnesis and due to normal laboratory results a «seronegative (RF), ACPA (CCP)-negative tenosynovitis without arthritis» had been reported. Diagnostic and therapeutic tenosynovectomy was performed. Histologic processing revealed a positive PCR for parvovirus B19. We discuss articular and extraarticular manifestations. A parvovirus B19-associated manifestation in the musculoskeletal system is usually self-limiting. The therapy should be carried out symptomatically. In our patient there was a marked local finding, so that the complete tenosynovectomy followed by a single steroid injection led to a persistent restitutio ad integrum.