My left foot! Pes cavus or high Arches is considered to be a foot deformity commonly found in neuromuscular diseases. Most texts will point a finger at Charcot-Marie-Tooth disease, of which the type1a variant is the genetic opposite of HNPP. In CMT1a there is a duplication of a region within Chromosome 17, which leads to an overexpression of the gene PMP-22 (Peripheral Myelin Protein). With HNPP the opposite is true, there is a deletion of the same region within Chromosome 17, which leads to underexpression of the gene PMP-22.
To be honest, I just thought everyone had feet like mine, I didn’t at anytime think that they were abnormal. Mostly it does not cause any pain or difficulty walking, although pes cavus rarely develops on it’s own, and if a neuropathy is the cause then there is also likely to be other foot and lower leg problems. For example, peroneal muscular weakness, numbness in the feet and lower leg, in the case of HNPP this will likely be in a consistent dermatomal distribution, with CMT1a it may well have a ‘stocking-like’ distribution.
I have had episodes of foot drop, which is due to the weakness in the lower leg, to make things difficult this has often been quite variable, but that seems fairly consistent with the presentation of HNPP. With CMT1a the resulting foot drop is likely to be more permanent as the slowly progressing generalised polyneuropathy develops. HNPP seems more chaotic in it’s progression, and although it can present as a generalised polyneuropathy it is more likely to present as a patchy multifocal neuropathy with an episodic nature.
I have had foot inserts made to help support my arches, and during episodes of foot drop I have a TOE-off lower leg brace, AFO – Ankle Foot Orthoses, it’s cumbersome but extremely light and strong, being made from composite materials. It helps to stop my foot from rolling over and dropping on leg raise. My right foot is actually worse than my left, and this asymmetry is also indicative of HNPP rather than CMT which is on the whole symmetrical.