Development of thyroid follicular adenoma on simvastatin therapy

HMG-CoA reductase inhibitors (lovastatin, simvastatin, fluvastatin, pravastatin) constitute a potent class of cholesterol-lowering agents, which are increasingly being used these days for primary and secondary prevention of atherosclerotic heart disease. Despite having good overall safety and efficacy profiles, these medications can still cause significant adverse effects including transient elevation of hepatic transaminases, myopathy, and rhabdomyolysis. Preclinical studies have demonstrated a potential of neoplasia in rats. However in clinical trials HMG-CoA reductase inhibitors have not been found to be neoplastic in humans. The dosage used in humans is also significantly lower and therefore it is expected to have a good safety margin. But this may not be entirely true considering the mechanism of neoplastic transformation, which is thought to be different in humans as compared to other species. We report a patient, who developed follicular adenoma with prominent Hurthle cell changes after being on simvastatin for three months but not during one year of pravastatin therapy. In elderly female patients with hyperlipidemia requiring pharmacologic treatment, especially those with a prior history of multinodular goiter, one should consider using an agent which has not been shown to cause thyroid tumors even in animal models. Patients should continue to be followed with frequent periodic thyroid palpation in addition to the usual biochemical monitoring required while on these agents.