Congenital insensitivity to pain with anhidrosis: a case with preserved itch sensation to histamine and partial pain sensation

Summary Congenital insensitivity to pain with anhidrosis is a rare autosomal recessive hereditary disorder that is characterized by having both sensory neuropathy and anhidrosis. A 6‐year‐old Japanese boy presented with recurrent fever, lack of sweating, occult bone fractures and impaired pain sensation without mental retardation. Genetic analyses revealed compound heterozygous mutations in the NTRK1 gene that encodes TrkA, which is a receptor for nerve growth factor. While there were no apparent changes in the patient’s dermal eccrine glands, the quantitative sudomotor axon reflex test with acetylcholine chloride revealed a complete loss of both the axon reflex‐mediated and the directly activated sweat responses. On the other hand, the histamine prick test induced a normal weal response surrounded by a flare phenomenon. Notably, the patient felt both an itch sensation after histamine and a burning sensation after topical capsaicin application. Consistent with these findings, PGP9.5+ nerve fibre innervation of the papillary dermis was observed, although the fibres were completely absent around the eccrine glands. These findings suggest that there was a partial preservation of the nerve endings that express the H 1 receptor and/or TRPV1 in the upper dermis, even though there were mutations of the NTRK1 gene in this case.