Congenital insensitivity to pain and anhidrosis with mitochondrial and axonal abnormalities.

Hereditary sensory and autonomic neuropathy type IV, or congenital insensitivity to pain with anhidrosis (CIPA), is a rare clinical disorder with only 32 cases reported in the literature. There has been no consistent pathophysiologic defect of the sensory nerve detected by light microscopic examination, but a frequent finding of decreased small myelinated fibers and a uniform finding of decreased unmyelinated fibers by ultrastructural analysis has been reported. Muscle biopsy in a 2-year-old boy with congenital insensitivity to pain with anhidrosis indicated lipid droplet accumulation and reduced cytochrome C oxidase histochemically on light microscopy. Electron microscopic study showed almost absent small unmyelinated nerve axons within the muscle, increased microfilaments, and decreased microtubules in axons, some abnormally enlarged mitochondria, and normal-appearing motor endplates. Biochemical analysis of muscle mitochondrial enzyme function revealed cytochrome c oxidase function to be reduced to 35% of normal, with normal function of the other mitochondrial enzymes.