Cat scratch disease presenting as fever of unknown origin is a unique clinical syndrome.

Fever of unknown origin (FUO) is a rare manifestation of cat scratch disease (CSD). Data regarding CSD associated FUO (CSD-FUO), particularly in adults, are limited. We aimed to study disease manifestations and long-term clinical outcome.A national CSD surveillance study is conducted in Israel since 1991. Data are obtained using questionnaires, review of medical records and telephone interviews. FUO was defined as fever of >14 days without an identifiable cause. CSD-FUO patients were identified in the 2004-17 CSD national registry. Follow-up included outpatient clinic visits and telephone/e-mail surveys.The study included 66 CSD-FUO patients. Median age was 35.5 (range 3-88) years. Median fever duration was 4 weeks (range 2-9). Relapsing fever pattern was reported in 52%, weight loss in 57% and night sweats in 48% of patients. Involvement of >1 organs occurred in 59% of patients; hepatosplenic space-occupying lesions (35%); abdominal/mediastinal lymphadenopathy (20%), ocular disease (18%) and multifocal osteomyelitis (6%) being the most common. Malignancy, particularly lymphoma was the initial radiological interpretation in 21% of patients; 32% underwent invasive diagnostic procedures. Of the 59 patients available for follow-up (median duration 31 weeks, range 4-445), 95% had complete recovery of symptoms; 3 patients remained with ocular sequelae.This is the first attempt to characterize CSD-FUO as a unique syndrome which may be severe and debilitating and often mimics malignancy. Relapsing fever is a common clinical phenotype. Multi-organ involvement is common. Recovery was complete in all patients except in those with ocular disease.