This supplementary information is presented as submitted by the corresponding author. It has not been copy-edited by NTvG.

Hypothyroidism is a well-known cause of secondary dyslipidemia and may predispose to the development of atherosclerotic disease. Measurement of thyroid hormone levels are however often not included in the screening of dyslipidemic patients. We describe two cases with hypothyroidism-induced dyslipidemia in whom the lipid abnormalities after substitution of the thyroid hormone completely resolved.

The first case is a 50-year old woman referred by the general practitioner with dyslipidemia and uncontrolled hypertension despite blood pressure lowering medication. The patient complained of tiredness, swollen ankles and easy weight gain. Laboratory tests revealed high levels of low-density lipoproteins (LDL) and total cholesterol, and overt hypothyroidism. The diagnosis of hypothyroidism-induced dyslipidemia is made and after treatment with solely levothyroxine therapy for two months cholesterol levels normalize. The medication for hypertension was not changed and the blood pressure reached normal values within 1 months.

The second case is a 49-year old man with complaints of shortness of breath, muscle aches and decreased renal function. After blood test the diagnosis of hypothyroidism with secondary dyslipidemia, myopathie and renal insufficiency was made. Seven months after start of levothyroxine treatment, the complaints resolved and the cholesterol levels normalize.

De prevalence of higher levels of TSH in patients with dyslipidemia is around 12-13%, compared to 2% in the normal population. In hypothyroidism both increased levels of total cholesterol concentration and of serum LDL cholesterol are found. Decreased thyroid function increases both the number of LDL particles in the blood, but also promotes LDL oxidability thereby increasing the atherogenic effect. Statins are less effective in hypothyroid patients whose HMG-CoA reductase (the rate limiting enzyme in cholesterol biosynthesis) activity is already reduced by the hypothyroid state. Hypothyroidism is by itself a risk factor for myopathie en renal insufficiency, however it also increases the risk of statin-induced rhabdomyolysis.

Ladies and gentlemen, these cases illustrate that clinical and biochemical screening for thyroid dysfunction is of paramount importance in all dyslipidemic patients, before start of lipid-lowering medication. These cases also show the diversity in clinical presentations which makes that the diagnoses is often missed. Treatment of the thyroid disorder potentially improves dyslipidemia and reduces the risk for cardiovascular disease. In general, it takes 4-6 weeks of replacement therapy with levothyroxine to correct dyslipidemia in overt hypothyroidism.