A case of thyrotoxicosis-induced anemia in a patient with painless thyroiditis

Background There have been several reports of secondary anemia associated with Graves’ disease. There are no reports of secondary anemia resulting from thyrotoxicosis due to painless thyroiditis (silent thyroiditis). We report the case of a patient with pancreatic diabetes who developed anemia caused by thyrotoxicosis due to painless thyroiditis. Case presentation The patient was a 37-year-old man who visited the hospital complaining of fatigue, palpitations, and dyspnea. His hemoglobin was 110 g/l (reference range, 135–176), and mean corpuscular volume was 81.5 fl (81.7–101.6). His free thyroxine (FT4) was high, at 100.4 pmol/l (11.6–21.9); the free triiodothyronine (FT3) was high, at 27.49 pmol/l (3.53–6.14); TSH was low, at < 0.01 mIU/l (0.50–5.00); and TSH receptor antibody was negative. Soluble IL-2 receptor (sIL-2R) was high, at 1340 U/ml (122–496); C-reactive protein (CRP) was high, at 6900 μg/l (< 3000); and reticulocytes was high, at 108 109 /l (30–100). Serum iron (Fe) was 9.5 (9.1–35.5), ferritin was 389 μg/l (13–401), haptoglobin was 0.66 g/l (0.19–1.70. Propranolol was prescribed and followed up. Anemia completely disappeared by 12 weeks after disease onset. Thyroid hormones and sIL-2R had normalized by 16 weeks after onset. He developed mild hypothyroidism and was treated with L-thyroxine at 24 weeks. Conclusions This is the first case report of transient secondary anemia associated with thyrotoxicosis due to painless thyroiditis. The change in sIL-2R was also observed during the clinical course of thyrotoxicosis and anemia, suggesting the immune processes in thyroid gland and bone marrow.


Background
Secondary anemia associated with hyperthyroidism is a relatively rare complication [1]. Many reports have shown that although anemia progresses with hyperthyroidism in Graves' disease, it is often transient, improving with treatment of Graves' disease [2][3][4]. There are no reports of secondary anemia resulting from thyrotoxicosis due to subacute thyroiditis, painless thyroiditis (silent thyroiditis) [5], or other causes. Here, we report a case of transient anemia that developed after the onset of painless thyroiditis in a patient with pancreatic diabetes treated with insulin.
The patient was previously diagnosed with pancreatic diabetes due to alcoholic pancreatitis at age 25 years, and thus, he was treated with a combination of insulin glargine and insulin aspart. Regular clinical examinations were performed every 28 days, and no abnormalities were found in his biochemical data or complete blood count, other than his plasma glucose and HbA1c. Propranolol (30 mg/day) was prescribed at day 14 and stopped on day 56. Thyroid ultrasonography was performed on day 28, and hypoechoic regions were observed throughout the thyroid gland (Fig. 1).
The anemia disappeared by day 84. The patient's thyroid hormones and sIL-2R normalized by day 112, and CRP normalized by day 140. The clinical courses of Hgb, FT4, and sIL-2R were shown in Fig. 2. There was slight decrease in LDL-C and HDL-C, and increases in liver enzymes at disease onset, but these changes disappeared by day 140 (Table 1). His serum albumin was low at onset but normalized by day 140. The patient's insulin regimen was not changed over the entire clinical course. He developed mild hypothyroidism on day 112 and was started on 12.5 μg of L-thyroxine replacement therapy on day 168 (Table 1).

Discussion and conclusions
We reported a case of painless thyroiditis-induced thyrotoxicosis that suddenly led to anemia within 4 weeks after the patient's last visit to our hospital. Although it was not possible to prove reduced iodine uptake using thyroid scintigram, negative TSH receptor antibody, the mild increase of CRP, lack of tenderness in thyroid gland, and the diffuse destructive findings on thyroid ultrasonography indicated painless thyroiditis [5]. In addition, FT3/FT4 ratio (0.301) was low, suggesting painless thyroiditis, because the median (IQR) of FT3/FT4 ratio in painless thyroiditis was reported as 0.310 (0.203-0.608) [6]. This is the first report of secondary anemia associated with painless thyroiditis. Although the levels remained within the normal range, slight decrease in WBC and platelets presented at disease onset [1]. Anemia, and the decrease in WBC and platelets completely disappeared by 12 weeks after onset, with spontaneous remission of thyrotoxicosis.
In addition to the clinical course of thyrotoxicosis and associated anemia, the present case provided interesting laboratory data. First, sIL-2R was high at onset but normalized by 16 weeks after onset of anemia. Elevated levels of sIL-2R have been reported in hyperthyroidism of Graves' disease and it was suggested that thyroid hormones directly enhance sIL-2R production in lymphocytes [7]. The levels in sIL-2R also increased in patients with the thyrotoxicosis due to painless thyroiditis [8]. Second, LDL-C and HDL-C levels decreased due to thyrotoxicosis. Excessive thyroid hormone levels lower serum LDL-C and HDL-C levels via several mechanisms [9][10][11]. We previously reported that increased sIL-2R cause significant decreases levels in HDL-C and LDL-C in patients with hematologic malignancies [12]. Increased cytokines were recently reported to be associated with hypolipidemia in COVID-19 patients [13]. Presumably, increases in levels of both thyroid hormones and sIL-2R are associated with the decreases in HDL-C and LDL-C.
Painless thyroiditis (silent thyroiditis) is a self-limiting inflammatory disorder of the thyroid gland characterized by an early thyrotoxicosis phase caused by the release of thyroid hormones and a late hypothyroidism phase, with complete resolution in most cases [5,14]. The pathophysiologic mechanism of painless thyroiditis is unknown, but the possibility of immune disorder involvement has been suggested [5,7,8,15]. Painless thyroiditis generally manifests as a lymphocyte infiltration of the thyroid follicles, causing thyroid follicular cell damage [5]. In our case, we observed a typical course of painless thyroiditis. The secondary anemia caused by thyrotoxicosis has improved, but we would like to carefully follow up on the continuation of thyroid hormone replacement therapy.
The mechanism by which anemia develops in thyrotoxicosis is not clear. Shortened erythrocyte survival or ineffective erythropoiesis have been suggested as potential causes of anemia in thyrotoxicosis [2][3][4]. Moreover, slight decrease in WBC and platelets was observed in present case, which could have been due to a variety of mechanisms. The involvement of autoantibodies in leukocytes and platelets resulting in increased destruction of hematopoietic cells by immunological mechanisms has been reported [16]. The increase in sIL-2R, which had been increasing at the onset of painless thyroiditis, may suggest the result of immune process abnormality rather than the increase in thyroid hormones [8,17]. The involvement of immune processes in the onset of painless thyroiditis could help explain the  Fig. 1 Thyroid ultrasonography findings. Hypoechoic regions are scattered throughout the thyroid gland. No increase in blood flow in the thyroid gland was observed pathophysiology of anemia [18]. In present case, however, both anti-TG and anti-TPO antibodies were negative. Anti-thyroglobulin and anti-TPO antibodies prevalence in painless thyroiditis have been reported to be 70 and 30%, respectively [19]. The patient had an history of acute pancreatitis. It is interesting to assume the immune mechanisms as the pathogenesis of acute and chronic pancreatitis [20], and it is natural to assume that the immune mechanism was involved in the development of silent thyroiditis and anemia in present case.
In conclusion, we reported the case of a diabetes patient with secondary anemia resulting from thyrotoxicosis. Thyrotoxicosis was caused by painless thyroiditis, but there have been no reports of secondary anemia induced by painless thyroiditis. The change in sIL-2R was also observed during the clinical course of thyrotoxicosis and anemia.