Dyslipidemia Unmasked by the Treatment of Graves' Disease: The Link Between Cholesterol Metabolism and Thyroid Hormones.

Thyroid dysfunction can alter serum lipid levels, which can delay the diagnosis of hyperlipidemia. We report the case of a 44-year-old female in whom dyslipidemia was unmasked following the treatment of Graves' disease. The diagnosis of Graves' disease was made after the patient presented with fatigue, weight loss, palpitations, tremors, and shoulder pain. At that time, laboratory testing showed suppressed thyroid-stimulating hormone (TSH), free thyroxine (T4) of 2.39 ng/ml (normal: 0.7-1.48 ng/ml), total triiodothyronine (T3) of 3.36 ng/ml (normal: 0.4-1.93 ng/ml), thyroxine-receptor antibody (TRAb) of 9.07 IU/l (normal: ≤1.75 IU/l), thyroid-stimulating immunoglobulin (TSI) of 7.57 IU/l (normal: ≤0.54 IU/l) and a normal lipid panel (total cholesterol: 140 mg/dl, low-density lipoprotein (LDL) of 79 mg/dl, high-density lipoprotein (HDL) of 43 mg/dl, and triglyceride (TG) of 90 mg/dl). After treatment with methimazole for a year, the patient achieved euthyroidism (TSH: 2.043 mcIU/ml, free T4: 0.93 ng/ml, total T3: 1.28 ng/ml) but had dyslipidemia (total cholesterol: 257 mg/dl, LDL: 174 mg/dl, HDL: 51 mg/dl, TG: 161 mg/dl). There had been no change in the patient's diet or lifestyle. It was thought that improvement in hyperthyroidism had unmasked underlying dyslipidemia.  The patient declined statin therapy and chose to pursue stricter lifestyle modifications. The cholesterol panel showed improvement eight months later (total cholesterol: 186 mg/dl, LDL: 114 mg/dl, HDL: 47 mg/dl, TG: 124 mg/dl) with ongoing euthyroidism (TSH: 2.099 mcIU/ml, free T4: 0.97 ng/ml, total T3: 1.24 ng/ml). This report highlights the close relationship between thyroid hormones and cholesterol metabolism. It reviews the pathways through which thyroid hormones affect cholesterol metabolism. The report emphasizes the importance of monitoring lipid profiles in patients with thyroid dysfunction. Conversely, thyroid function testing should be done in patients presenting with lipid abnormalities.