Severe Gastrointestinal Graft-versus-Host Disease Following Haploidentical Stem Cell Transplantation Presenting With Passage of a Colonic Cast.

Gastrointestinal graft-versus-host disease (GI-GVHD) is a life-threatening complication of allogeneic hematopoietic stem cell transplantation with increased severity in haploidentical settings. We report a fatal case of severe, steroid-refractory GI-GVHD in a 67-year-old male following haploidentical stem cell transplantation for myelodysplastic syndrome with excess blasts-2. The patient developed multiorgan complications including refractory cytopenias, severe infections, pleural effusions, and hepatic dysfunction. A rare and striking manifestation occurred with the passage of a colonic cast, reflecting profound mucosal injury and full-thickness epithelial sloughing. Despite maximal immunosuppressive therapy, including corticosteroids, calcineurin inhibition, ruxolitinib, and extracorporeal photopheresis, the patient deteriorated and ultimately expired. This case highlights an extreme presentation of GI-GVHD with rare colonic cast formation and emphasizes the aggressive nature of steroid-refractory disease.