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Cyclic thrombocytopenia (CTP) is a very rare blood disorder characterized by periodic fluctuations in platelet counts. Each of the fluctuations is usually over a period of 3-5 weeks. The levels that the platelet counts reach have been reported as from 10 × 109 /L at the lowest and climbing to 330 × 109 /L at the peak. Therefore, patients may oscillate between periods of severe thrombocytopenia, with all its implications, or rebound recovery to levels where there is an increased risk of thrombosis.
Due to the symptoms following the low platelet counts, CTP may be misdiagnosed as immune thrombocytopenia (ITP). However, distinct from ITP, CTP generally responds poorly to most treatments used successfully in ITP such as corticosteroids, splenectomy, and intravenous immunoglobulin. There is no clear idea of the cause of CTP although (as in ITP) autoimmune platelet destruction is thought likely, but bone marrow abnormalities with poor megakaryocyte function, infectious causes and hormonal changes have all been considered as potential mechanisms.
Interestingly, CTP was more commonly found in females, a predominance disproportionately in favour of pre-menopausal women, and these fluctuations of platelets are often in phase with the menstrual cycle, suggesting an association of the hormonal cycle with fluctuations in the platelet count. a possible pathogenesis of CTP and suggests promising therapeutic strategies for the disease.
Making the correct diagnosis can be difficult and any patient diagnosed with ITP, who shows unexpected fluctuations in their count should be considered as having CTP and a platelet count diary should be maintained, if possible off all treatment, to follow the trend in the counts. Treatment can be difficult and steroids are often given initially but there is anecdotal evidence that thrombopoietin receptor agonists, such as romiplostim and eltrombopag, may be helpful in reducing the fall in the counts but they may have the unwanted effect of markedly increasing the peaks. They should be used with caution and only under close medical supervision and it goes without saying that treatment should only be considered if there is a bleeding risk. Unfortunately, many patients fail to respond to any therapy. The disease is chronic and may go on for years although occasional examples of spontaneous remissions have been recorded.
Professor Adrian Newland