The next step was genetic testing for hereditary neuropathy with liability to pressure palsies (HNPP) which showed deletion of PMP22 gene.

HNPP is an autosomal dominant disease caused in up to 90% of cases by deletion of a 1.5 Mb section of  chromosome 17p11.2, which contains the  gene coding for PMP22. The remaining cases are caused by point mutations in the same gene. HNPP is characterized by recurrent motor and sensory mononeuropathies, mainly at the entrapment sites. Mononeuropathy may emerge after mechanical compression of the nerve, for example after heavy exertion or prolonged positioning of a limb. The most commonly affected nerves are peroneal and ulnar; followed by brachial plexus, radial and median. Involvement of the cranial nerves and neuropathic pain are reported but uncommon. The peak age of onset is second to third decades, but cases have been reported with the onset of symptoms at birth to the eighth decade. The deficits usually improve in a matter of hours to weeks, but residual motor deficits may be present in 10-15%. On the other hand, HNPP can progress to long-term peripheral neuropathy phenotypically indistinguishable from CMT1; pes cavus has been reported in 4-47% of cases in different case series. Nerve conduction study shows slowing at the entrapment sites (median nerve at wrist, ulnar nerve at the elbow, peroneal nerve at the fibular head) even in asymptomatic cases.  Conduction blocks may be present, specially during the acute stage. Motor nerve conduction velocities are usually normal in the other segments. There may also be significant slowing of the sensory nerve responses. HNPP can be differentiated from CMT1, as in the latter there is diffuse slowing (rather than segmental slowing in HNPP) and no conduction blocks. The management is largely symptomatic. No controlled studies are done so far to assess whether surgical decompression of the nerves is beneficial. Patients should avoid activities that cause nerve compression such as prolonged crossing of the legs, leaning on elbows, or rapid loss of weight.

Suggested reading:

van Paassen BW, van der Kooi AJ, van Spaendonck-Zwarts KY, Verhamme C, Baas F, de Visser M. PMP22 related neuropathies: Charcot-Marie-Tooth disease type 1A and Hereditary Neuropathy with liability to Pressure Palsies. Orphanet journal of rare diseases. 2014;9:38.