SCH is defined as suppressed serum TSH (below the lower limit of the reference range) in the setting of normal serum free T3 and T4. In the United States, SCH has a prevalence between 0.7% and 15.4%, depending on the regional dietary iodine intake and age of the population.3 Given the presence of a nodule in the gland, a likely cause of SCH in this patient is a toxic uni- or multinodular goiter. Although Graves disease, subacute thyroiditis, and drug-induced thyroiditis are potential causes of SCH, they are not likely the cause of this patients hyperthyroidism. Graves disease is less likely given the presence of a nodule; subacute thyroiditis is unlikely because the timing of disease onset is not consistent with thyroiditis and the thyroid was not tender on physical examination; and drug-induced thyroiditis is unlikely given that the patient only takes aspirin, which is not associated with thyroiditis. SCH must be carefully differentiated from euthyroid sick syndrome by repeated monitoring of serum TSH levels over time. Most patients with SCH present without symptoms.
- SCH from a toxic adenoma.
3. Papi G, Pearce EN, Braverman LE, et al. A clinical and therapeutic approach to thyrotoxicosis with thyroid-stimulating hormone suppression only [published erratum appears in Am J Med 2005;118:933]. Am J Med 2005;118:349-61.
4. Sawin CT, Geller A, Wolf PA, et al. Low serum thyrotropin concentrations as a risk factor for atrial fibrillation in older persons. N Engl J Med 1994;331:1249-52.
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