SP30 | UNUSUAL CLINICAL PRESENTATION OF A HYPEREOSINOPHILIC SYNDROME INITIALLY MISDIAGNOSED AS ULCERATIVE COLITIS, FOLLOWED BY SULFASALAZINE-INDUCED DRESS SYNDROME

Introduction: Hypereosinophilic syndrome (HES) is a rare (0.36/100,000/year), heterogeneous group of disorders defined by persistent eosinophilia >1,500/μL, exclusion of secondary causes, and evidence of tissue or organ involvement. If untreated, it can lead to significant morbidity and mortality. Case Presentation: A 32-year-old woman with a recent diagnosis of ulcerative colitis, treated with sulfasalazine 1 g/day and oral mesalazine 1 g TID, presented in August 2023 with fever (39°C), vomiting, and a photosensitive rash. Sulfasalazine was discontinued due to suspected adverse reaction. Rash progression and cervical lymphadenopathy prompted multiple ER visits, with minimal benefit from corticosteroids and antihistamines. Lab tests showed leukocytosis (21.9 ×10⁹/L) with eosinophilia (3.2 ×10⁹/L), increased liver enzymes, LDH, and β2-microglobulin. Infectious and autoimmune causes were ruled out. Persistent fever, rash with marked periorbital edema, and hepatosplenomegaly raised suspicion for DRESS syndrome, confirmed by dermatologic evaluation. Results: During hospitalization, HHV-6 DNA was detected. Imaging revealed lymphadenopathy (up to 21 mm in short axis) and hepatosplenomegaly (spleen 145 mm). Hematologic workup showed the presence of a FIP1L1-PDGFRA fusion transcript (<30%), suggesting clonal eosinophilic disease. BCR-ABL transcript was negative. Bone marrow biopsy showed increased eosinophil precursors and normal karyotype (46 XX [20]); immunophenotyping revealed increased circulating CD3+ T cells (both CD4+ and CD8+ subsets). Skin biopsy revealed chronic perivascular dermatitis. Re-evaluation of colonic biopsies showed a marked eosinophilic infiltrate previously overlooked. Imatinib 100 mg daily was started, resulting in rapid clinical and hematologic improvement. The patient currently maintains a complete response without adverse events or toxicity. Conclusion: This case illustrates the diagnostic complexity of overlapping DRESS and clonal HES, particularly following recent drug exposure. It highlights the importance of multidisciplinary workup in patients with persistent eosinophilia and systemic involvement (Figure 1).