Behçet's syndrome is a systemic vasculitis. Gastrointestinal involvement in Behçet's syndrome complicated by myelodysplastic syndrome represents a rare and severe subtype for which no standardized treatment guidelines currently exist, posing significant challenges in clinical practice. Ustekinumab, a biologic agent targeting IL-12/IL-23, has demonstrated favorable efficacy in both gastrointestinal Behçet's syndrome and inflammatory bowel disease. This study aims to evaluate the efficacy and safety of ustekinumab in patients with intestinal Behçet's syndrome and coexisting myelodysplastic syndrome.

This is a multicenter, single-arm clinical trial designed to evaluate the efficacy and safety of ustekinumab in patients with intestinal Behçet's syndrome complicated by myelodysplastic syndrome (MDS). A total of 8 patients with intestinal Behçet's syndrome and concomitant MDS will be enrolled. Prior to enrollment, all patients will discontinue any previous biologic agents. Ustekinumab will be administered subcutaneously at a dose of 90 mg at weeks 0, 4, and 8, followed by a maintenance dose of 90 mg every 12 weeks (every 3 months). All patients will be followed for a total of 24 months.

Clinical manifestations, inflammatory biomarkers, and endoscopic findings will be documented throughout the study period. Concomitant medications will be recorded, and adverse events will be systematically monitored to evaluate the efficacy and safety of the treatment.

Inclusion Criteria:

Meet the 2014 International Criteria for Behçet's Disease (ICBD) for the diagnosis of Behçet's syndrome; Have a confirmed diagnosis of myelodysplastic syndrome (MDS) by bone marrow aspiration and/or biopsy; Have confirmed intestinal ulcers on colonoscopy; Aged between 18 and 70 years; Have active disease at enrollment, defined as a Behçet's Disease Current Activity Form (BDCAF) score ≥ 1; Provide signed informed consent.

Exclusion Criteria:

Presence of one or more other autoimmune diseases; Involvement of other vital organs (e.g., cardiovascular, neurological) requiring treatment with other biologic agents or high-dose corticosteroids; Receipt of surgical treatment; Severe trilineage cytopenia attributed to myelodysplastic syndrome; Presence of acute or chronic active infection (e.g., bacterial, or viral infections such as EBV, CMV, HIV, or active hepatitis virus) within 4 weeks prior to enrollment; Current or prior history of any malignancy; Pregnancy or within 6 months postpartum; Presence of severe liver failure (Child-Pugh Class C) or end-stage renal disease requiring dialysis.