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PROF FROM RX
This patient has the euthyroid sick syndrome, a mild, transient form of central hypothyroidism that often occurs during systemic illness. During non-thyroidal illness such as pneumonia, many patients develop reduced thyroid-stimulating hormone (TSH) and reduced thyroxine (T4), a similar profile to patients with central hypothyroidism from pituitary insufficiency. This usually resolves when the non-thyroidal illness resolves. Thyroid hormone replacement is not beneficial among these patients.
Because the euthyroid sick syndrome is so common, testing of thyroid function is rarely done in hospitalized patients (a huge clinical pearl for students on inpatient medicine rotations). When testing is done to evaluate for primary thyroid disease, measurement of reverse triiodothyronine (rT3) levels can distinguish between central hypothyroidism and euthyroid sick syndrome. Reverse T3 is an isomer of T3. Levels of rT3 typically parallel T4 levels (high in hyperthyroidism, low in hypothyroidism). In patients with non-thyroidal illness leading to the euthyroid sick syndrome, rT3 levels will be high.
This patient with non-thyroidal illness and euthyroid sick- syndrome should have a reduced TSH, reduced T4, and increased rT3.
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