Central and Proximal Myelin Damage of Cranial Nerves in Hereditary Neuropathy with Liability to Pressure Palsies

Objective: We have attempted to provide evidence for central and proximal nerve myelin damage of cranial nerves in hereditary neuropathy with liability to pressure palsies (HNPP). Methods: Eight patients with the diagnosis of HNPP, which is due to a heterozygous deletion of PMP22 gene, were investigated consecutively. The results of MRI scans of the brain, evoked potential studies (MEP, VEP, AEP), and reflex studies of the motor and sensory cranial nerves (blink reflex, masseter reflex, jaw-opening reflex) were performed and categorized either as suspicious of myelin damage or normal by means of potential latencies and T₂ hyperintensity. The control group for the electrophysiological studies consisted of 48 healthy individuals, matched for age and gender. Results: Four patients showed pathological hyperintense T₂ lesions in MRI. MEP studies were suspicious of demyelination in 11/64 measurements (2/135 controls; p<0.0001), evoked potentials showed pathological latencies in 15/42 measurements (9/188 controls; p<0.00001), and finally reflex studies brought up evidence for central as well as peripheral myelin damage in 7 of 24 measurements (4/55 controls; p<0.01). Conclusions: This study provides systematic and significant evidence in a small-sized consecutive population of HNPP patients for functionally relevant myelin damage of the central nervous system and proximal cranial nerves, indicating not only a possible clinical role for diagnosis and prognosis of HNPP, but also a possible role for PMP22 pathology in the central myelin structure in general.