Endocrine Abstracts

Background: Neutropenia due to anti-thyroid drug (ATD) therapy in Graves’ disease is rare but is well recognised. However, the effect of hyperthyroidism, prior to and after ATD therapy, on absolute neutrophil counts in patients with Graves’ disease is unclear.

Methods: We noted neutrophil levels in consecutive patients with newly diagnosed Graves’ thyrotoxicosis in 2010–2013. We further noted neutrophil levels once patients had been treated with ATD for at least 3 months and were rendered euthyroid. A neutrophil count of <2×10⁹/l was classed as neutropenia. Neutrophil levels at baseline and after euthyroidism was achieved were compared by paired Student’s t-test. Multivariable linear regression analysis was performed to ascertain factors affecting change in neutrophil levels.

Results: At initial diagnosis of Graves’ thyrotoxicosis and prior to initiation of ATD, 24/147 (16.3%) individuals had neutropaenia. Compared to individuals without, those with neutropenia were more likely to be younger (42.1 vs 50.3 years; P=0.02), have more severe hyperthyroidism (FT₄ levels of 67.6 vs 45.3 pmol/l; P<0.001), less likely to be current smokers (20.8 vs 34.1%; P<0.01) and have Graves’ orbitopathy (25 vs 15.4%; P=0.01). After multivariable regression analysis, severity of hyperthyroidism (P<0.005) and non smoking status (P=0.02) were the only independent predictors of neutropenia and there was no association with TBII levels. After euthyroidism was achieved, none of the patients in the neutropaenic group (n=16) remained neutropaenic. Furthermore, neutrophil levels increased significantly (3.8 vs 4.8 10⁹/l; P<0.001) even in patients that were not neutropenic at baseline (n=74). Improvement in neutrophil count was related to reduction in thyroid hormone levels (P<0.001) and was more pronounced in males.

Conclusions: Graves’ thyrotoxicosis is associated with neutropenia in about a sixth of patients at diagnosis. This improves with treatment with ATD due to reduction in thyroid hormone concentrations. It is therefore crucial to check neutrophil levels in newly diagnosed patients with Graves’ thyrotoxicosis prior to commencing ATD therapy as otherwise low levels may incorrectly be attributed to ATD therapy.