Crohn's Disease and Axial Spondyloarthritis: From Systemic Inflammation to Amyloidosis.

Background: Crohn's disease (CD) is frequently complicated by extraintestinal manifestations, including axial spondyloarthritis (axSpA). Both diseases share genetic (HLA-B27, IL23R, ERAP1/2) and immunopathological mechanisms (Th17/IL-23 axis). Their co-occurrence increases the risk of systemic complications such as AA amyloidosis. Case presentation: We report a 42-year-old male with HLA-B27-positive axSpA who developed CD shortly after initiating secukinumab (IL-17A inhibitor). Following discontinuation of secukinumab and surgical management of CD, the patient experienced rapidly progressive AA amyloidosis affecting the kidneys and intestines, leading to acute kidney injury and requiring hemodialysis. Potential triggering factors included a preceding intestinal infection and self-administered infrared physiotherapy. Conclusions: Coexistent CD and axSpA significantly increases the risk of severe AA amyloidosis. IL-17 inhibitors should be used with extreme caution in patients with subclinical or active CD. Early screenings for proteinuria and low-threshold biopsy are essential to detect AA amyloidosis. In patients with both conditions, TNF-α or IL-12/23 inhibitors are preferred over IL-17 blockade.