Levothyroxine and potassium iodide are both effective in treating benign solitary solid cold nodules of the thyroid

To determine the effectiveness of levothyroxine and potassium iodide in treating patients with benign solitary cold thyroid nodules.

Randomized controlled study.

Outpatient clinic at a university hospital.

80 patients with solitary solid cold thyroid nodules found to be benign at cytologic examination were randomly assigned to no treatment, suppressive levothyroxine (thyroid-stimulating hormone level, < 0.3 mU/L), or low-dose potassium iodide (2 mg every 2 weeks). Seventy patients completed the 1-year study. After 1 year, patients receiving treatment discontinued drug therapy and were re-evaluated 4 months later; patients receiving no treatment were given levothyroxine and were followed for a second year.

Nodule volume was measured by ultrasonography at 4-month intervals by an observer masked to treatment assignment.

Mean nodule volume decreased by 40% of the basal volume in the 23 patients receiving levothyroxine (P < 0.001) and by 23% of the basal volume in the 25 patients receiving potassium iodide (P = 0.053). Volume slightly increased in the 22 untreated patients (P = 0.085). A clinically relevant reduction in nodule volume (> or = 50%) was observed in 9 of 23 patients treated with levothyroxine, in 5 of 25 patients treated with potassium iodide, and in none of 22 untreated patients (P = 0.004). Only nodules with a volume of 10 mL or less were reduced; nodules with volumes of 5 mL or less shrank most frequently. Nodule volume did not relevantly increase in treated patients but did increase in 3 of the 22 untreated patients. Drug withdrawal resulted in an increased mean nodule volume (P = 0.004) after 4 months.

Levothyroxine and, to a lesser extent, potassium iodide are effective in arresting the growth or in reducing the volume of benign solitary solid cold thyroid nodules, especially small ones; discontinuation of therapy may result in resumed nodule growth.