What thyroid disorders should be considered when TSH is suppressed and thyroid hormone levels are normal or elevated in the setting of ICPI therapy?
Suppressed serum TSH levels with normal or elevated thyroid hormone values would suggest autoimmune hyperthyroidism (Graves’ disease) or the hyperthyroid phase of destructive thyroiditis. Patients with autoimmune hyperthyroidism often have a diffusely enlarged thyroid gland, elevated thyroid-stimulating immunoglobulins (TSIs), or positive thyrotropin receptor antibodies (TRABs) and increased homogenous uptake on an iodine-123 ( 123 I; radioactive iodine [RAI]) scan, whereas patients with destructive thyroiditis usually have a normal-size thyroid gland, normal TSI or TRAB levels, and decreased uptake on an 123 I scan. The clinician should also be alert for other underlying causes of thyroid dysfunction, such as medications (amiodarone or lithium) or recent iodinated contrast administration, which may exacerbate underlying thyroid disease and limit the utility of RAI. In addition, central hypothyroidism, characterized by low serum free T 4 levels and low or inappropriately normal serum TSH levels, can occur especially in the setting of CTLA-4 inhibitor use.