Idiopathic cyclic thrombocytopenia.

Cyclic thrombocytopenia (CTP) is an uncommon disorder characterized by periodic fluctuations in platelet counts, typically resulting in episodes of thrombocytopenia alternating with normal platelet counts. While some CTP cases are associated with a primary hematologic disease, most are idiopathic. Patients with CTP are frequently misdiagnosed as idiopathic thrombocytopenic purpura (ITP) because CTP has clinical features very similar to ITP. When evaluating patients with suspected ITP, CTP should always be included in the differential diagnoses because CTP generally does not respond to standard ITP treatments, including corticosteroids, splenectomy, and intravenous immunoglobulin. Two clinical features relatively unique to CTP besides periodic thrombocytopenia are rebound thrombocytosis unrelated to recent splenectomy and platelet nadirs occurring during menses. When a diagnosis of CTP is made, patients must be offered a period of observation, as many may not require treatment. If treatment is clinically indicated, the literature suggests that hormonal therapy provides the best response.