Flare-Ups in Chronic ITP: A Proposal for a Clinical Sub-Phenotype "Acute-on-Chronic ITP".

Immune thrombocytopenia (ITP) is a heterogeneous disorder with fluctuating platelet counts. Current classifications do not adequately capture acute exacerbations in stable chronic ITP patients. We describe two chronic ITP patients with long-term stable platelet counts who experienced sudden, symptomatic thrombocytopenic flares. Both were managed with short courses of corticosteroids or IVIg while continuing prior therapy. Outcomes were assessed clinically and hematologically over extended followup. Both patients showed rapid and sustained responses, returning to baseline platelet counts without long-term therapy escalation. These episodes were distinguishable from refractory ITP by their identifiable triggers, episodic course, and excellent response to short-term treatment. We propose diagnostic criteria, key differentiators from refractory ITP, and a management algorithm. Acute on Chronic ITP is a distinct clinical entity characterized by sudden platelet declines in stable ITP patients, responsive to shortterm therapy. Recognizing this phenotype may prevent overtreatment, reduce healthcare costs, and improve patient outcomes. Formal incorporation into future ITP guidelines is warranted.