Congenital insensitivity to pain with anhidrosis.

A nine-year-old child presented with congenital insensitivity to pain and anhidrosis. Quantitative studies and electron microscopy of the cutaneous branch of the radial nerve revealed almost complete absence of small myelinated and unmyelinated fibers and a disproportionate number of nerve fibers with a diameter of 6-10 micrometers. A grouping of both type 1 and type 2 muscle fibers was also seen. We suggest that this disease entity is not caused by a hereditary sensory neuropathy, but rather that it derives from a developmental defect.