Differential diagnosis
Congenital insensitivity to pain with anhidrosis may be misdiagnosed for leprosy, based on similar symptoms of severe injuries to the hands and feet.
Clinical description
Charcot joints are demonstrated in this boy with HSAN IV or congenital insensitivity to pain with anhidrosis (CIPA). The right knee and right ankle (on the left of the picture) are enlarged and distorted. The skin over the medial aspect of the ankle is darkened with a draining would secondary to superimposed osteomyelitis. There are other areas of trauma and ulcers including a site on the right heel.
Patients with this disorder are very likely to injure themselves in ways that would normally be prevented by feeling pain. The main features of the disorder are lack of pain sensation, painless injuries of the arms, legs and oral structures, hyperthermia during hot weather because of inability to sweat, mental retardation as a result of hyperthermia, infection and scarring of the tongue, lips and gums, chronic infections of bones and joints, bone fractures, multiple scars, osteomyelitis and joint deformities, which may lead to amputation. Other common problems are eye related, such as infection due to the sufferers rubbing them too hard, too frequently or scratching them during sleep. In addition, patients typically lack unmyelinated and small myelinated nerve fibers in the dorsal root ganglion. Both are responsible for transmitting pain signals. In addition, patients’ sweat glands are normal in both structure and function, though they lack innervations by small diameter neurons
Treatment
Treatments for CIPA do not always work; however, there are some cases where naloxone may be used as a treatment. Naloxone is a chemical that acts within the nervous system of the body by blocking the nervous system from causing the inactions that occur within the group of cells that receives the message to initiate the sensation of pain, heat, or cold. Most treatments are hard to narrow down for this condition because each CIPA patient may have other conditions including the absence of a sweat gland, nerve fibers, ulcers[disambiguation needed], and other sub-conditions. It has been suggested that young CIPA sufferers have their baby teeth removed so they cannot chew through their tongue, lips or fingers until their full set of adult teeth grow through.
Cause
CIPA is caused by a genetic mutation which prevents the formation of nerve cells which are responsible for transmitting signals of pain, heat, and cold to the brain. The disorder is autosomal recessive. It does not appear to have any particular ethnic distribution, though it is more prevalent in cultures in which intermarriage is an accepted practice.Overheating kills more than half of all children with CIPA before age 3.
The genetic mutation is in the gene encoding the neurotrophic tyrosine kinase receptor (NTRK1 gene).NTRK1 is a receptor for nerve growth factor (NGF). This protein induces outgrowth of axons and dendrites and promotes the survival of embryonic sensory and sympathetic neurons. The mutation in NTRK1 does not allow NGF to bind properly, causing defects in the development and function of nociceptive reception.
