Clinical Description
NTRK1 congenital insensitivity to pain with anhidrosis (NTRK1-CIPA) is characterized by profound sensory loss affecting pain and temperature perception, absence of sweating (anhidrosis), and intellectual disability.
Anhidrosis. Because sweating plays an important role in maintaining normal body temperature, anhidrosis (the failure to sweat) disturbs thermoregulation in hot environmental conditions and increases susceptibility to recurrent febrile episodes [Indo 2002, Indo 2018].
Recurrent episodic fevers, usually the first clinical sign of NTRK1-CIPA, can begin in infancy or early childhood depending on environmental temperature. Recurrent febrile convulsions are also observed in some affected infants.
Occasionally, hypothermia is observed in cold environments.
Anhidrosis is present on the trunk and upper extremities in 100% of cases and more variable in other areas of the body [Ismail et al 1998, Axelrod 2002]. Although with warming the intertriginous areas of the neck, axillae, and groin can become slightly moist, no definite sweating is noted. This moisture is probably due to delayed insensible water loss.
Insensitivity to pain. While impaired pain perception may not be apparent in early infancy, parents may recall that their infant with NTRK1-CIPA did not cry during venipuncture or immunizations [Indo 2002, Indo 2018].
Tongue ulcers and fingertip biting, the characteristic self-mutilation signs observed in infants with NTRK1-CIPA, begin when the primary incisors erupt, and can result in a bifid or absent tongue. Although taste buds are normal, traumatic injuries of the tongue, such as a partial loss of papillae and scar formation, may cause secondary hypogeusia or decreased taste sensation [Amano et al 1998].
Biting of the fingers and ulcerated fingertips is common.
Bruises, cuts, and burns do not elicit normal reactions and are often unrecognized at the time that they occur. Accidental injuries such as falls or burns lead to multiple scars and can lead to cellulitis in the skin.
Orthopedic problems are one of the most characteristic and serious complications of NTRK1-CIPA [Bar-On et al 2002, Kim et al 2013].
Frequent orthopedic complications:
Multiple fractures often with hyperplastic new bone formation, avascular necrosis, and osteomyelitis
Auto-amputation, self-mutilation (including self-inflicted soft tissue injuries)
Leg length discrepancy
Joint subluxation and dislocation resulting in Charcot neuroarthropathy of the feet, ankles, knees, and hips
Septic arthritis
Progressive scoliosis
Amputations of fingers or limbs are common as a result of these complications.
Decreased pain perception does not spare any area, affecting even cranial nerves and visceral sensation [Yagev et al 1999, Shorer et al 2001].
Neurotrophic keratitis (degenerative disease of the corneal epithelium resulting from impaired corneal sensation) manifests initially as superficial punctate keratopathy which later can result in corneal ulceration and even perforation [Yagev et al 1999, Amano et al 2006, Mimura et al 2008]. Of note, tearing (both overflow or emotional) is normal.
Intellectual disability. Most individuals with NTRK1-CIPA have varying degrees of intellectual disability and show characteristic behaviors [Indo 2002, Indo 2018]. Affected individuals show defects in conceptual thinking, abstract reasoning, and social behavior, as well as moderate to severe emotional disturbance. Some may exhibit rage. Assessments of cognitive and adaptive behavior suggest that many children with NTRK1-CIPA have intellectual disability (or learning disabilities) and severe attention-deficit/hyperactivity disorder [Levy Erez et al 2010].
Irritability, hyperactivity, impulsivity, and acting-out behaviors typically improve with age.
The prognosis for independent functioning varies.
Other
Often the skin is dry with lichenification; the nails are dystrophic. Palmoplantar hyperkeratosis (thickening of the soles and the palms) appears in late infancy, often with scars and abrasions [
Bonkowsky et al 2003]. Significant fissuring of the plantar skin is common. Some affected individuals develop deep heel ulcers that are slow to heal [
Mardy et al 1999].
Hypotonia is seen frequently in the early years, but strength and tone normalize as the individual gets older; tendon reflexes are normal [
Axelrod 2002].
Gastrointestinal dysmotility is mild or absent.
Vomiting is not a feature, but can be observed in some affected individuals.
Speech is usually clear.
Normal findings
Touch, vibration, and position senses
Motor functions (unless repeated trauma has caused secondary dysfunction of motor neurons or limbs)
Deep tendon reflexes and superficial abdominal and cremasteric reflexes
Neurophysiology of NTRK1-CIPA
See Indo [2018] (full text) for information on the neurophysiology of NTRK1-CIPA.