Congenital pain insensitivity is a rare genetic disorder characterized by the inability to perceive pain. Since affected individuals do not respond appropriately to painful situations, they engage in self-mutilating behavior such as biting of the oral mucosa and fingers and sustain injuries such as burns, fractures, and joint dislocations.
Congenital pain insensitivity (CPI) is an autosomal recessive disorder characterized by the inability to discern physical pain although the ability to feel a stimulus is intact . This rare ailment is considered to be a part of the hereditary sensory and autonomic neuropathies (HSAN) . CPI is a genetically heterogeneous disease caused by mutations in the SCN9A , NTRK1 , and NGFB genes . If left undetected and unaddressed, this condition can affect the patient's overall health and result in serious outcomes.
The clinical presentation reflects which gene is affected. Generally, the cases demonstrate a lack of pain perception with burns, bone fractures, joint dislocations, and other injuries . Moreover, they engage in self-mutilation by biting on their tongue, lips, and digits   resulting in laceration and ulceration of oral mucosa and scarring of the cheeks  . Additionally, affected individuals may exhibit mental retardation and developmental delays with varying degrees. Also common are behavioral issues and emotional lability. Furthermore, patients may be prone to developing neurotrophic keratitis, corneal ulcerations and scarring, and even infection.
Painless injuries induce severe consequences such as recurrent disease and repeated fractures. Specifically, sufferers are susceptible to developing osteomyelitis, acroosteolysis, and Charcot joints. Additionally, they may develop oral ulcers and other lesions, which further lead to infections, oral bleeding, and malnutrition . If not treated, poor outcomes such as failure to thrive are likely .
The neurologic exam in subjects with CPI reveals normal touch, vibration, and position senses. Remarkable overall findings include joint deformities, disfiguring injuries, oral and eye abnormalities.
Infants and young children with an impaired response to pain and repeated harmful behaviors should be evaluated for this medical entity. The workup will include the patient's history and presentation, a complete physical exam (including a focus on neurologic, oral, and eye tests), and specialized studies.
Biopsy of the skin and nerves can confirm the diagnosis by revealing distinctive findings . Specifically, microscopic analysis of the skin may show the abnormal functioning of nerves innervating eccrine sweat glands while examination of the nerve tissue may demonstrate a diminished quantity of unmyelinated small-diameter fibers. Another exam is characterized by applying pressure with a pen onto the patient's nail bed. Note that an absent withdrawal response is a result of the lack of pain perception . Clinicians may perform the axonal flare test, in which an intradermal histamine injection results in a characteristic skin response. An electromyogram (EMG) will typically yield normal results . Genetic testing is not routinely done since there are many mutations associated with CPI.