Rapid Reversal of Severe Thrombocytopenia after Cessation of Diazoxide in a 1.7-Year-Old Girl with Hyperinsulinemic Hypoglycemia

Background: Hyperinsulinism-hyperammonemia (HI/HA) syndrome is a rare genetic form of hyperinsulinemic hypoglycemia. While diazoxide is the first-line medical therapy for this condition, it has been associated with several adverse effects, ranging from fluid retention to rare hematologic complications. Case Description: A 1.7-year-old girl with HI/HA syndrome, confirmed by a monoallelic pathologic variant in the GLUD1 gene (c.1466C>A, p.Pro489His), presented with a sudden onset of generalized ecchymoses, petechiae, and wet purpura. These symptoms emerged three weeks after initiating diazoxide therapy at 5 mg/kg/day. Investigations revealed severe isolated thrombocytopenia (platelet count 4 x 109/L). An elevated immature platelet fraction (10.5%) and a low one-hour corrected count increment following platelet transfusion suggested an immune-mediated destructive process. Diazoxide was immediately discontinued. Following a single platelet transfusion and cessation of the drug, the patient’s platelet count recovered rapidly, normalizing within 48 hours and reaching 487 x 109/L two weeks after. Conclusion: This case highlights a rare but severe presentation of diazoxide-induced thrombocytopenia in a pediatric patient. Laboratory confirmation of an immune process, most likely via a quinine-type mechanism, is consistent with the patient's rapid recovery. Clinicians should maintain a high index of suspicion for hematologic toxicity among patients treated with diazoxide, as prompt discontinuation of the offending agent leads to rapid clinical and laboratory recovery.