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Table 1 Key features of CMT1A and HNPP

From: PMP22 related neuropathies: Charcot-Marie-Tooth disease type 1A and Hereditary Neuropathy with liability to Pressure Palsies

  CMT1A HNPP
Duplication of PMP22 Deletion of PMP22
Clinical features Age of onset mainly in first two decades Painless attacks of numbness, muscular weakness, and atrophy, recurrent and focal
Presenting symptom is difficulty walking or running
Preceded by minor compression on nerve
Distal symmetrical muscle weakness and wasting, legs > arms
Age at onset mostly in the second or third decade
Pes cavus very frequent Pes cavus found in 4-47% of patients
Sensory symptoms (stocking-glove distribution) usually less prominent, legs > arms
Full recovery in 50% of episodes, usually in days to weeks
Pain more common than previously recognized Sequelae rarely severe
Large intrafamilial clinical variability
  Reflexes absent or depressed
Large clinical variability between patients, even within family
Electrophysiological features Homogeneous and diffuse MCV and SCV slowing Increase in distal motor latencies, especially of median and peroneal nerve
CMAP amplitudes reduced, especially distally in the legs
Focal motor slowing at entrapment sites
SNAP amplitudes frequently reduced to absent
MCV normal to slightly reduced in other segments
SCV decreased and SNAP amplitudes often reduced
Neuropathological features Abnormal myelination over the whole nerve length Segmental de-and remyelination
Onion bulbs Tomacula pathologic hallmark, but not pathognomonic
Decreased density of myelinated nerve fibres
Variable large-fibre loss
  1. CMAP = compound muscle action potential. MCV = motor conduction velocity. SCV = sensory conduction velocity. SNAP = sensory nerve action potentials.