[Pancytopenia resolved by the treatment of hyperthyroidism]

Hyperthyroidism can be associated with various haematological disorders related to several mechanisms. These disorders might be related to the reduced life-span of whole blood components and/or to an autoimmune mechanism. Only one case of pancytopenia has yet been reported. The observation of 3 new personal cases (1 toxic adenoma and 2 Graves' disease) led us to review the pathogeny of haematological disorders found in hyperthyroidism. Only one patient had antineutrophil autoantibodies. Direct and indirect Coomb's test, and Dixon's test were negative. In all patients, bone marrow aspiration was unable to demonstrate pernicious anaemia or myelodysplastic syndrome. Two patients presented cytological signs of macrophage activation with eosinophilia. These cytological features were compatible with an immuno-allergy mechanism. All haematological disorders disappeared when patients became euthyroid. In all cases, the haematological abnormalities were quite mild and might have gone unnoticed. Thus, it can be suggested that the frequency of pancytopenia in hyperthyroidism is underestimated.