CHICAGO — Immunologic thrombocytopenia was associated with an increased prevalence of thyroid disease in a retrospective longitudinal study.
The finding argues for routine screening for thyroid disease in patients with immunologic thrombocytopenia. The study also indicated that treating the thyroid disease did not influence the long-term course of the thrombocytopenia, Dr. Adriana Ioachimescu and her colleagues at the Cleveland Clinic Foundation reported in a poster at the annual meeting of the American Association of Clinical Endocrinologists.
American Society of Hematology guidelines on immunologic thrombocytopenia, last updated in 1996, state that thyroid function evaluation has “uncertain appropriateness” in adults with immunologic thrombocytopenia. Testing is considered appropriate only before elective splenectomy to rule out occult hyper- or hypothyroidism.
Thyroid function tests, available in 80 of 98 patients consecutively diagnosed with immunologic thrombocytopenia by a single provider between 1988 and 2005, indicated 20% had thyroid disease. Ten were hypothyroid and six were hyperthyroid. Patient ages ranged from 21 to 75 years, and the average follow-up was 131 months. The onset of the two conditions was simultaneous in 4 of the 16 cases.
The study represents the largest cohort and longest follow-up of patients with both conditions, Dr. Ioachimescu said in an interview. Only three studies evaluating the association between the two disorders have been published since 1931. Based on these studies, the estimated prevalence of thyroid disease in patients with immunologic thrombocytopenia would be 5%–14%, she said. The prevalence of hyper- or hypothyroidism is about 5%–6% in the general population.
In Dr. Ioachimescu's study, all patients with hypothyroidism received thyroid supplementation and eventually reached a normal level of thyroid-stimulating hormone. Five of the six patients with hyperthyroidism became hypothyroid after radioactive iodine treatment, and needed thyroid hormone supplementation. The sixth patient with hyperthyroidism remained euthyroid after methimazole therapy.
Of the 16 patients with thyroid disease, 14 required treatment for their thrombocytopenia; medical therapy was provided in 13, and splenectomy was performed in 6.
Previous case reports of patients with both disorders have shown significant increases in platelet count after thyroid treatment. In the current study, platelet counts transiently increased in three patients after normal thyroid function was restored. No changes were seen in the other 13 patients. The discrepancy between findings could be due to publication bias, as case reports and case series tend to present positive findings, or because prior reported cases were associated with more severe hyperthyroidism, which affected platelet counts, she said.
Further studies are needed to determine if thyroid autoantibodies have a direct impact on the platelet count or whether they simply represent a marker of the autoimmune thyroid disease, Dr. Ioachimescu reported.