Ultralate cerebral potentials in a patient with hereditary motor and sensory neuropathy type I indicate preserved C-fibre function.

Late and ultralate cerebral potentials in response to cutaneous heat (CO2 laser pulses) and electrical nerve stimuli were studied in a patient with hereditary motor and sensory neuropathy type I who showed severe impairment of myelinated nerve fibre function. Cerebral potentials in response to electrical stimuli were absent (tibial nerve) or small (median nerve). With the laser pulses applied to the foot only ultralate, but no late potentials were observed, indicating intact C-fibres, but disturbed A delta-fibres. Laser stimulation of the hand resulted in both late and ultralate components, indicating at least partly preserved A delta-fibre function. The results document the usefulness of laser stimuli in the assessment of small nerve fibre function.