Electromyographic recording of the jaw reflex in Friedreich ataxia.

Jaw jerk was studied in 10 subjects with Friedreich ataxia, and 10 normal subjects for comparison. Electromyographic recording from the right masseter muscle showed a reflex response in all cases, in contrast to the absence of tendon reflexes in the four limbs for the ataxics. The mean latency of the jaw jerk was normal. These observations indicate that the jaw reflex arc is preserved, and that no damage to the trigeminal neuromuscular pathway exists for all the patients observed.