Slow nerve conduction velocity in cretins.

The ulnar and posterior tibial conduction velocities were measured in 6 untreated and 3 treated cretins. In 4 of the untreated patients, the conduction velocity of both nerves was slower than normal; in 1 patient the ulnar and in the other the posterior tibial nerve conduction velocity was slower than normal. There was a close agreement between bone age and the age corresponding to the slow conduction velocities. The 3 treated cretins all had normal posterior tibial conduction velocities, while the ulnar conduction velocity was normal in one, slower in another, and faster than normal in the third. The slow nerve conduction velocity in cretins probably reflects a delay in maturation of the peripheral nerves. Nerve conduction velocity measurement may be a useful screening test in suspected congenital hypothyroidism, and may also prove of value in assessing response to therapy.