Hereditary neuropathy with liability to pressure palsy: two cases of difficult diagnosis.

Hereditary neuropathy with liability to pressure palsies (HNPP) is an inherited autosomal dominant disorder that causes a polyneuropathy with predisposition for involvement at sites of compression and is often underdiagnosed or misdiagnosed due to its heterogeneity in clinical and electrophysiological presentation. We report 2 cases of HNPP, which were initially diagnosed and treated as either an acquired demyelinating disorder or alternative inherited demyelinating disorder. Thorough evaluation of repeat electrodiagnostic studies and genetic testing confirmed the diagnosis of HNPP in both cases. One case showed the classic peripheral myelin protein 22 (PMP22) deletion and the other case showed a previously reported single base pair deletion at Leu145 causing a frameshift mutation at the PMP22 gene. These cases underscore the difficulty of diagnosing HNPP, because of the variations in clinical and electrophysiological findings and reinforce the importance of a combination high index of clinical suspicion, electrodiagnostic testing, and genetic testing to make the diagnosis.