Influence of Nonthyroidal Illnesses on Serum Thyroid Hormone Indices in Hyperthyroidism

Severe intercurrent nonthyroidal illnesses (diabetic ketoacidosis, myocardial infarction, fulminant hepatitis and bacterial pneumonia) in four thyrotoxic patients were associated with depression of total serum thyroxine (T(4)) and triiodothyronine (T(3)) values into the normal or even subnormal range. A diagnosis of hyperthyroidism was established by a combination of elevated radioactive iodine uptake, absent thyroid-stimulating hormone response to thyrotropin-releasing hormone or an elevated free T(4) by dialysis values. In the two of four cases that had a fatal outcome, there was a progressive decline in total T(4) and total T(3) values. In contrast, the two surviving patients had a progressive increase of total T(3) and total T(4) values into the hyperthyroid range as their underlying illness resolved. As has been seen with severe nonthyroidal illnesses, pronounced depression of total T(3) and total T(4) levels in hyperthyroid patients may also portend a poor prognosis.