Primary congenital hypothyroidism complicated by persistent severe anaemia in early infancy: a case report with a literature review

Abstract

Although anaemia is a common finding in adults with hypothyroidism, there is a general paucity of studies on anaemia in infants with congenital hypothyroidism. 1 The degree of anaemia is usually mild to moderate, with a haemoglobin concentration that is rarely less than 8-9 g/dl. 2 The associated anaemia in hypothyroidism is generally normochromic and normocytic, and occasionally mildly macrocytic. 1 This heterogeneity has been attributed to coexisting deficiencies of iron, vitamin B12 and folic acid, largely due to impaired absorption. 2,3 Anaemia in hypothyroidism has been linked to impaired haemoglobin synthesis due to a deficiency of thyroxine (T4). 3 There is evidence of a direct effect of the thyroid hormone on erythropoiesis. The pathogenesis of anaemia in hypothyroidism has been linked to either a lack of erythropoietin production, or a physiological adaptation to the decreased tissue oxygen requirements resulting from a decrease in the basal metabolic rate. 4 The red cell life span is normal and the results of ferrokinetic studies are compatible with hypoproliferative erythropoiesis in hypothyroidism. 5,6 Thyroid hormones affect oxygen needs at cellular level. Therefore, the responses are compatible with an appropriate physiological adjustment. 2 In vitro studies have shown that thyroid hormones potentiate the effect of erythropoietin on erythroid colony formation. 7 Conversely, iron deficiency impairs T4 synthesis by reducing the activity of haeme-dependent thyroid peroxidase. 8 White blood cell and platelet counts are usually unaffected in hypothyroidism. 2 Indeed, it has been stated that the presence of pancytopenia suggests that hypothyroidism is not primary, but instead relates to hypopituitarism. 9 In their report, Antonijevic Nesovic, Trbojevic and Milosevic 10 state that the presence of acanthocytosis in a peripheral blood smear suggests hypothyroidism in approximately 90% of cases. The response to thyroid hormone therapy is gradual. A slow improvement in haemoglobin concentration is seen over several months. 11 Children with a haematocrit value less than 21% and 15%, are considered to have severe anaemia and very severe anaemia, respectively. 12 We report on a case of a six-month old infant who presented with persistent severe anaemia, and who was found to have primary congenital hypothyroidism after a prolonged stay in hospital.