Fifteen patients with Charcot-Marie-Tooth type 1A (CMT1A) disease and 46 normal
controls were studied. In the patients, leg muscle strength, touch-pressure,
vibration and joint position sense were reduced; lower limb tendon reflexes were
absent in 12 or markedly decreased. Motor and sensory conduction velocity (CV) of
leg nerves was either reduced or not measurable. The Neurological Disability
Score and the Neuropathy Score were obtained from clinical and
electrophysiological examination, respectively. Tilt of a supporting platform
elicited short- (SLR) and medium-latency (MLR) responses to stretch in the foot
muscle flexor digitorum brevis (FDB) in controls. In the patients, the former
response was absent and the latter delayed. These findings are in keeping with
the known loss of large-diameter myelinated fibres, with relative sparing of the
smaller fibres. The MLR delay was fully accounted for by the slowed CV of the
motor fibres. The MLR afferent time was similar to that in normal subjects. Body
sway area (SA) during quiet stance was recorded with eyes open or closed, and
with feet apart or together. Under all postural and visual conditions, SA was
within normal range in the less severely affected patients, but was moderately
increased in the patients with a more severe neuropathy score. Across all
patients, no correlation was found between SA and muscle force, motor CV, touch
pressure, vibration and joint position sense, considered either separately or as
an aggregate. We suggest that: (1) functional integrity of the largest afferent
fibres is not necessary for appropriate equilibrium control during quiet stance
and (2) any unsteadiness is related to additional functional alterations in
smaller fibres, most likely group II spindle afferent fibres
