From parks to TOpClass: A collaborative approach to classification & treatment optimization in perianal Crohn's disease

Fistulizing perianal Crohn's disease (fpCD) affects approximately 25% of patients with Crohn's disease and carries a high symptomatic burden of disease and impairs quality of life (QoL). For 50 years, perianal fistulae have been classified anatomically according to the Parks classification, which describes the relationship between a tract and the internal and external sphincter complex. In 2022, the Treatment Optimization and Classification (TOpClass) Consortium reframed pCD by stratifying patients according to disease severity, specifically the impact on QoL and treatment goals, and whether the internal opening (IO) of the fistula is amenable to surgical repair (class 2a/b) or requires diversion (class 2c), proctectomy (class 3), and includes post-proctectomy sinuses and de novo fistulae (class 4). This review discusses the historic classifications of pCD and instruments used to measure disease activity, describes each TOpClass subgroup and its implications for surgical decision-making, including surgical rationalization and prevention of chronic presacral sinus after intersphincteric proctectomy, the role of magnetic resonance imaging as the optimal assessment of healing, and summarizes more than 20 TOpClass collaborative publications, including the validation of the classification in real-world cohorts, extension of the framework to isolated pCD (ipCD), non-fistulizing pCD (nf-pCD), and anorectal fistula-associated malignant pCD (mpCD). The TOpClass Consortium highlights the multidisciplinary, collaborative, and dynamic nature of pCD care. Overall, TOpClass has been a paradigm shift that has reinvigorated the field to focus on treatment optimization across the spectrum of pCD presentations.