Congenital hypothyroidism and IQ increase: a quarter century follow-up.

Ten patients with a history of congenital hypothyroidism were recalled for IQ evaluation 16 to 26 years after an original IQ test at age 5 to 6. From childhood through adulthood, the IQ (Wechsler) increased (mean full scale IQ increase = 21; range = -5 to 43 points). Serial testing in three instances showed the timing of the increase to be sudden and unpredictable. Life achievements, mental health, and sexual adjustment were concordant with the IQ attained. The data suggest that in hypothyroidism intellectual growth may not occur in equal annual increments; with effective hormonal replacement and educational experience it may be subject to spurts of growth, with a resultant improved prognosis.