Congenital insensitivity to pain with anhidrosis in a 2-month-old boy.

In a 2-month-old boy with congenital insensitivity to pain and anhidrosis, the initial symptom was recurrent fever of unknown origin. After eruption of the first teeth, self-mutilation of the tongue was limited by extraction of the teeth. Unmyelinated fibers were essentially lacking, and the number of small myelinated fibers was decreased in sural nerve. This case is the youngest to be diagnosed and the first one in which nerve biopsy clearly showed the characteristic findings.