The age at the onset of symptoms is very variable (first to
seventh decade of life). Gait disturbances are the predominant and often first sign of the
disorder. Foot deformities (pes cavus) with hyperreflexia of the leg and positive Babinski
sign may develop during the course of the disease. Amyotrophy of the intrinsic hand muscles
with marked muscle weakness and wasting can occur unior bilaterally and mainly affects the thenar
and dorsalis interosseus l muscles. (Rarely, it may also involve the feet). Generally, sensation
is preserved, except for an occasionally mild reduction in vibration sense in the lower
limbs in older patients. Neurophysiological studies favor anterior horn cell or motor nerve
root involvement rather than a generalized neuropathy. In particular, no evidence of concurrent
median or ulnar neuropathy could be found. However, median motor nerve conduction velocities
may be mildly reduced. Other features may include urinary urgency, urinary incontinence and
sphincter disturbances. In patients with the autosomal recessive inherited type of this
disorder, amyotrophy often begins in the first decade of life and spasticity dominates over
paraparesis. Severe muscle wasting of the thenar and hypothenar muscles may often coexist with
amyotrophy below the level of the knees and pes cavus deformity.