Imagine a life without any physical pain. It exists, and it's not as pleasant as you may think. Those who suffer from such a condition fail to notice broken bones or lacerations. They often mutilate themselves accidentally, may have mental handicaps, and rarely live into adulthood. Two individuals with a congenital absence of pain with hyperhidrosis (CAPH) were the subject of a study by researchers at the University of Liverpool's Pain Research Institution. These two were unique: despite their condition, they had lived normal lives. They came to the institute for excessive sweating, but soon were found to have pain thresholds two standard deviations above normal, and little sensation for pressure and temperature change. Scientists at the Albany Medical College in New York studied samples of their skin and discovered they were missing all the normal nerve endings normally associated with touch. How could they feel anything? Nerve endings attached to blood vessels and sweat glands, which scientists previously dismissed as unimportant, were sending tactile sensations to the brain. It was this secondary sensory system that had allowed the two individuals to live normal lives, preventing them from sustaining horrible injuries and to determine what was hot or cold, rough or smooth. A secondary sensory system in the skin is a remarkable find and could lead to a new understanding in how the body perceives touch. It could also shed light on painful conditions like migraines and fibromyalgia whose causes are not yet understood.
Chronic painful conditions affect hundreds of millions of people the world over, but pain itself is a subjective sensation. Scientists are often at odds over defining the cause of severe pain (like that found in fibromyalgia) as stemming from genetic disorders, psychological trauma, or physical injury. Sensations sent by your skin form the bulk of your perception of pain. With the new understanding of how nerves in your blood vessels and sweat glands can also send tactile sensations, scientists have an entirely new avenue of research to explore. It may be that these secondary sensations are behind certain cases of chronic pain. Also, if we find a way to selectively shut down the main pain receptors but leave the secondary system awake, we could have a means to create people who feel much less pain, but can still have enough sense of touch to function. What would we do with a superhuman tolerance for physical pain?
The work done at AMC, described in the journal Pain, takes advantage not only of a detailed look at the physical features in the skin, but also the genetic codes of the patients. Frank Rice, the head researcher, notes that the two patients don't have any special mutations in the common genes associate with skin nerve endings. This means that 1) there is likely some environmental factor that lead to the complete absence of normal nerve endings in the skin and 2) that the secondary sense system is likely dependent on a different set of genes. Rice also believes that even in normal patients, the secondary system is still sending tactile information to the brain.
Why don't we notice these sensations? Probably because the main signal is so much louder. It's only when the primary nerve endings are silenced (or absent) that an individual can use the secondary system to feel things (albeit with a much higher pain threshold). But what if seemingly normal individuals had secondary systems that suddenly flared up? What happens if the blood vessels and sweat glands start sending signals that are as loud as the primary nerves? It's total conjecture at this point, I wonder if cases like that may be the cause behind migraines, fibromyalgia, and other chronic pain conditions. Even if a malfunction in the secondary system isn't the cause for these problems, exploring the way it works may reveal equally important secrets on how the body perceives pain.
According to a press release, Rice, and another AMC colleague Phillip Albrecht have formed a company called Integrated Tissue Dynamics (aka Intidyn) to explore the chemical and structural conditions of the skin. It's exciting that even now there is still so much territory in the body that hasn't been fully explored. Who knows what kind of revelations are still to come. Once they have a better understanding of the human nervous system, scientists may be able to find means to fight pain more effectively. Eventually, we may move from treating painful symptoms of diseases, to managing our own sensation to improve our physical performance. Athletes, emergency workers, soldiers, or even average workers may be able to excel in extraordinary ways when pain can be removed without numbness. Just imagine.
[photo credit: The Med Guru]