Congenital insensitivity to pain

How is it produced?

Congenital insensitivity to pain is a rare hereditary disease that was first described in 1932 and in which there is an abnormal interpretation of painful stimuli associated with various degrees of autonomic dysfunction with an alteration in catecholamine levels.

In reality it is a heterogeneous group of diseases in which there is an injury to certain nerve fibers causing alterations in the stimuli they transmit. In the case of insensitivity to pain, there is an alteration of the small myelin fibers and the unmyelinated fibers, those that lack myelin, the sheath that covers the nerve bundles.

Among these diseases, called hereditary sensory autonomic neuropathies (NHSA), the IV form is the most common. It is an autosomal recessive disease, that is, it requires both copies of the gene that produces it to be altered for the disease to manifest itself, due to an alteration of the NTRK1 gene on chromosome 1, which causes an alteration in pain sensitivity as well as an atrophy of the sweat glands.

Symptoms

NHSA type I is very prevalent and is inherited autosomal dominant, it is enough that one of the copies of the gene that causes it is altered for the disease to manifest itself. There is a progressive loss of the sensation of pain and temperature and in the long run there is also a deficit in touch and in the perception of pressure. This form usually manifests itself in the second decade of life. They present a decrease in sweating as well as hearing loss.

NHSA type II, also called Morvan's disease, appears in childhood and there is an alteration of touch and sensitivity to pressure, as well as insensitivity to pain in varying degrees. In this type, the inheritance pattern is autosomal recessive, as in type IV discussed above.

Type III NSHA is called familial dysautonomia or Riley-Day syndrome, is also inherited in a recessive autonomic manner, and affects autonomic sensitivity, as well as the perception of pain and temperature. It manifests itself in neonates and they present difficulties with sucking, reflux of food, bronchial aspiration, lethargy, irritability, low muscle tone and decreased tendon reflexes.

As has already been said, the most frequent is form IV, congenital insensitivity to pain associated with anhidrosis, a lack of secretion from the sweat glands. Sensitivity to touch, temperature and pressure are preserved. Of autosomal recessive inheritance, the patients present marked insensitivity to painful stimuli, absence of sweating, and episodes of fever that were poorly controlled with drugs; in fact, 20% of patients die from excess temperature (hyperpyrexia) within the first three years of life.

The insensitivity to pain often causes injuries that can be serious. It is common to observe in those who suffer lesions of the oral mucosa, corneal ulcers of poor evolution, and especially musculoskeletal injuries, with fractures, septic arthritis, dislocations, or even autoamputations.

The skin usually has a callous appearance, with multiple wounds that are healing, cracks, ulcers and nail lesions. This syndrome is often associated with a certain degree of mental retardation; patients tend to express themselves normally but have learning difficulties.

NHSA type V is similar to the previous one; it manifests as insensitivity to pain and a partial alteration of sweat production, and also there are alterations in the perception of temperature.

Diagnosis

The diagnostic suspicion of these diseases is essentially based on the clinic, seeing children who do not respond to painful stimuli as they should, or seeing frequent skin lesions, mucosa or fractures. It is important to examine the patient's family history for cases of the same pathology.

In the and, alterations in catecholamine levels can be evidenced depending on the degree of alteration of the autonomic nervous system that the form of NHSA with which the patient is affected presents.

It is convenient to perform a physiological study using an electroneurogram (ENG) to assess the degree and type of nerve involvement. The definitive certainty will be given by a skin biopsy, in which an alteration of the nerve fibers involved in the conduction of the painful stimulus will be appreciated, as well as the atrophy of the sweat glands.

Treatment

Congenital insensitivity to pain is untreated. At best, what can be done is to take precautions to avoid injuries to the skin and bone as much as possible, adapting the child's environment and examining him frequently for possible injuries of which he has not been aware.

Precautionary measures

As it is a hereditary disease, there are no preventive measures. In case of having ancestors who suffer from it, it is advisable to take it into account when having offspring.

• It consists of an abnormal interpretation of painful stimuli.
• The insensitivity to pain often causes injuries that can be serious.
• As it is a hereditary disease, it has no treatment, but measures can be taken to avoid injuries to the bone and skin.