Segmental hyperhidrosis in two siblings with Chiari type I malformation.

A marked, left-sided segmental hyperhidrosis, verified by quantitative evaporimetry, corresponded to an area of dissociated sensory loss in 2 siblings (male 49 years old, female 47 years old). MRI scans of the head and whole cord demonstrated a Chiari type I malformation in both. In the male, there was a syrinx of the neck. The level of this did not correspond to the hyperhidrosis and dissociated sensory loss areas of the trunk and thigh. The female, who had no syrinx, had hyperhidrosis and dissociated sensory loss of the head, neck, upper trunk, and arm, and anisocoria with the larger pupil ipsilateral to the sweating. This rare disorder may be due to a disinhibition of the preganglionic sympathetic neurons caused by cord lesion(s) interrupting inhibitory descending and spinal pathways which are important for the normal thermoregulatory sweating.