Intermittent hydrarthrosis (periodic synoviosis): A narrative review.

Intermittent hydrarthrosis (IH), also termed periodic synoviosis or periodic benign synovitis, is a rare cause of recurrent, self-limited joint effusion-most frequently involving the knee-with striking periodicity and complete intercritical recovery. Despite being recognized for decades, IH remains underdiagnosed and is often mistaken for palindromic rheumatism, crystal-induced arthritis, septic arthritis, proliferative synovial disorders, and autoinflammatory syndromes. Historical descriptions emphasized a benign, non-destructive course, minimal systemic inflammation, and a lack of specific biomarkers [1, 2]. More recent reports suggest that, in a subset of patients, IH may overlap with autoinflammatory mechanisms, including associations with MEFV mutations and clinical responses to colchicine or IL-1 blockade [3-6]. This narrative review synthesizes available evidence on terminology, clinical spectrum, diagnostic work-up, hypothesized pathophysiology, differential diagnosis, and therapeutic options, and proposes a pragmatic approach for clinicians.