Hemophagocytic lymphohistiocytosis triggered by Hashimoto thyroiditis during pregnancy: a rare case report and diagnostic challenge.

Background: Hemophagocytic lymphohistiocytosis (HLH) is a rare and potentially fatal hyperinflammatory syndrome marked by the excessive activation of macrophages and cytotoxic lymphocytes. Although typically secondary to infections, malignancies, or systemic autoimmune diseases, its association with organ-specific autoimmune conditions such as Hashimoto's thyroiditis is uncommon, particularly during pregnancy. Case presentation: A 27-year-old pregnant woman at 22 weeks gestation with a 3.5-year history of Hashimoto's thyroiditis presented with progressive jaundice, high-grade fever, hepatosplenomegaly, and pancytopenia. Laboratory evaluation revealed hyperbilirubinemia, elevated lactate dehydrogenase (LDH), and hyperferritinemia. Infectious, malignant, and systemic autoimmune causes were excluded. HLH was diagnosed based on HLH-2004 criteria, despite the absence of hemophagocytosis on bone marrow biopsy. She was treated with corticosteroids and cyclosporine. Due to clinical deterioration, a medically supervised delivery was performed at 24 weeks, resulting in neonatal survival and maternal improvement. Clinical discussion: The diagnosis of HLH in pregnancy is challenging due to overlapping physiological changes. In this case, Hashimoto's thyroiditis and pregnancy-induced immune modulation may have contributed to immune dysregulation. Early multidisciplinary intervention and immunosuppressive therapy led to favorable outcomes. Conclusion: This case highlights the need for high clinical suspicion of HLH in pregnant patients with autoimmune conditions and systemic inflammatory symptoms. Prompt recognition, multidisciplinary management, and consideration of early delivery are critical to optimizing maternal and fetal outcomes.