Congenital insensitivity to pain

Congenital insensitivity to pain (or congenital analgia) is a rare condition where a child cannot feel (and has never felt) physical pain.

Presentation
Cognition and sensation is otherwise normal; for instance they can still feel discriminative touch (though not always temperature), and there is no detectable physical abnormality.

These children often suffer oral cavity damage both in and around the oral cavity (such as having bitten off the tip of their tongue) or fractures to bones. Unnoticed infections and corneal damage due to foreign objects in the eye are also seen. Because the child can not feel pain, he may not respond to problems, thus being at a higher risk of more severe diseases or otherwise.

In some people with this disease, there may be slight mental retardation, as well as an impaired corneal reflex.

Causes
There are some cases where the condition is caused by increased production of endorphins in the brain, in which case naloxone may be used as treatment. This treatment does not always work.

Gene SCN9A has been identified as a major factor in the development of the pain-perception systems within the body. A rare genetic mutation in this area causes non-functional development of certain sodium channels in the nervous system, which prevents the brain from receiving messages of physical damage. People having this disorder are completely ignorant to pain, and can perform without pain any kinds of self mutilation or damage. In the families studied, this has ranged from biting of the person's own tongue leading to damage, through to street acts with knives, to death from injuries due to a failure to have learned limits on injury through experience of pain. The same gene also appears to mediate a form of hyper-sensitivity to pain, with other mutations seeming to be "at the root of paroxysmal extreme pain disorder" according to a 2006 report in Neurone. Various other forms of somatic sensitivity are unaffected. Hyper-sensitivity to pain is also experienced in Erythromelalgia, or Mitchell's disease, which is another mutation of the same gene.

Types of congenital pain indifference
There are generally two types of non-response exhibited.
 * Insensitivity to pain means that the painful stimulus is not even perceived: a patient cannot describe the intensity or type of pain.
 * Indifference to pain means that the patient can perceive the stimulus, but lacks an appropriate response: they will not flinch or withdraw when exposed to pain.