Hyperinnervation Supersensitivity
The following is provided for basic education on this topic for members of the public, and does not go into this topic at the level discussed amongst doctors. If you are having pain after an injury, please consult with your doctors.
Healing after an injury
When tissues of the body are injured, the body lays down similar fibers to stabilize the tissue regardless of whether it is a movable and contractile tissue (such as muscle and tendons), or intended to stabilize joints (such as ligaments.) Damage can also occur in joint structures of the spine such as intervertebral discs and facet joints.
When these tissues are damaged by trauma, the result of new fiber deposits to heal result in tissue being layed down in an unorganized fashion that does not follow the normal physiology of muscle, tendon, ligament or other structures of the body. As an example, while muscle tissue within a single muscle is all organized into contractile units called actin and myosin that all run in one direction and slide over each other in mucle units called sarcomeres, some of the repair fibers will lay down in the correct direction while others will lay down diagnonally or even at 90 degrees to the original contractile unit. This is often referred to as scar tissue. This is one part of a traumatic injury that can result in pain and problems with function after trauma. Without treatment this tissue will never heal correctly or move in the same way as the original tissue.
Within the scar tissue the nerves that have been damaged in the area start to proliferate into the healing tissue. In an early article on this issue published in Science, titled "Hyperinnervation of Skeletal Muscle Fibers" it is noted that normally muscle fibers are usually innervated by a single motor nerve fiber. After injury that same muscle can now be innervated by multiple nerve fibers. "In both these cases the formation of new synapses is associated with supersensitivity to ACh." Meaning all of the nerves fire more easily.
Using our example of an injured muscle, new muscle fibers lay down in ways that are not aligned with the original structure. And in many cases it lays down too many nerve fibers in the area of injury. This is referred to as the "fibrosis of repair." With these nerve fibers sensing pain (or "nocioception") and sensing motion of the area so that your brain can locate your body and its various parts in space (called "proprioception") the nerves are now picking up abnormal signal because the tissue is not normal and does not move normally. The nerve fibers can over-proliferate in the area, a condition that some health providers call "hyperinnervation" of small fibers in the peripheral nervous system. Having more small nerve fibers leading to more sensitivity than normal, a condition referred to as "supersensitivity."
In an article published by the U.S. National Institutes of Health, it is now believed this is due to local Nerve Growth Factor (NGF) occurring at the injury site. The article notes "The nervous system adapts to changing conditions, however, and sympathetic neurons undergo structural and functional alterations in response to injury...." (This article addresses the complex physiologic mechanism by which this works if you are interested in learning more about the science.)
This supersensitivity of the nerve fibers can provide increased feedback of pain sensations from the injured area.
One part of this is that a person can end up with permanent supersensitivity of the nerve fibers in an area of injury. Under normal circumstances, nerves fire when a very small electrical charge called an "action potential" fires from one neuron to the next. When you have more small fiber nerves firing in an area, it is more likely that the action potential will be reached for an axon to send the signal toward the brain. Some also argue that the stimulus necessary to fire nerves decreases due to overproliferation of nerve fibers within scar tissue.
In some cases a persons nervous system can become so sensitive that changes in the atmopheric pressure caused by changes in the weather can increase the person's pain.
One of the purposes of chiropratic, physical rehabilitation, and physical therapy after a traumatic injury is to help breakdown fibers that are not aligned to the normal physiology of that tissue so that the body sends less abnormal pain stimulus to the brain. Despite some doctors and therapists best efforts, some people will still experience permanent pain from injuries that do not fully heal. In fact, over 90 medical journal articles published since the 1950s demonstrate that people who sustain traumatic spinal injuries end up having chronic pain that does not go away in 6-12 weeks, as the insurance companies and their doctors claim.
Meteorapathy: Increased Symptoms Caused by Changes in the Weather
Cloudy with a Chance of Pain
Pain caused by changes in the weather was first recognized as far back as the time of Hippocrates in 400 B.C., long before people had insurance claims. Hippocrates documented the connection between changes in weather and a person experiencing increased pain. He suggested that people often felt increased aches and pains when the weather fluxuated, particularly with changes in temperature and barometric pressure.
The first medical journal publication in modern times to document a change in pain associated with the weather was published in the American Journal of the Medical Sciences in 1887. This involved a single case report describing a person with phantom limb pain from an amputation, and it concluded that "approaching storms, dropping barometric pressure and rain were associated with increased pain complaint." [The article is not available in digital form, but is cited here.]
Despite people reporting this for over 2000 years, insurance companies will still claim that a person complaining of pain with changes in weather has a personality disorder or is malingering an injury that doesn't exist.
Hyperinnervation Supersensitivity is likely one part of a condition now referred to as Meteorapathy - condition in which changes in weather cause increased symptoms in a wide variety of body systems.
Rather than Meteorapathy being caused by depression or another psychological condition, the U.S. National Institutes of Health have recognized that it is the other way around. "Increasing evidence indicates that meteoropathy may affect mental health, leading to aggressive behavior, depression, sleep disorders, fear, and suicide [9]. Bellini et al. showed that the intensity of meteoropathy is correlated with levels of depression."
For a personal injury case, if you have Meteorapathy, its pretty important that you have a law firm that understands that the psychological impact comes from the injury, not the other way around. It is because of our understanding of small but important health issues like this one that injured people hire our firm instead of other law firms.
New Ways to Track Meteorapathy
In a recent study, 2658 people with a history of pain for the prior three months were followed for 15 months using a smartphone app called uMotif (available on iPhone and Android) to track the correlation between weather changes and pain (as well as many other factors.)
“This study has demonstrated that higher relative humidity and wind speed, and lower atmospheric pressure, were associated with increased pain severity in people with long-term pain conditions. The most significant contribution was from relative humidity.”
Unfortunately, several of our clients have permanent pain after their serious injuries. As an example, 90 peer reviewed medical journal articles support that people have chronic pain after a traumatic spinal injury. In some cases this permanent chronic pain can be aggravated by changes in the weather. This is particularly true in Oregon and Washington where the area experiences regular changes in atmospheric pressure. Unfortunately traumatic injuries create conditions that result in post-injury Meteorapathy that can be aggravated multiple times per day.
Worse Headaches with Weather Changes
The impact of changes in the weather on injuries is not isolated to connective tissues like muscles, tendons, ligaments and joint capsules. According to the Mayo clinic, migraine headaches may be triggered by changes in the weather. The United Kingdom's National Health System states "...weather changes are thought to trigger chemical and electrical changes in the brain. This irritates nerves, leading to a headache." A 2023 study published in the journal Headache found that in a large study size of 1,000,000 patients "low barometric pressure, barometric pressure changes, higher humidity, and rainfall were associated with an increased number of headache occurrences."
If you have experienced a significant injury as the result of a person or company's negligence, and are having ongoing permanent pain, hire a law firm that understands the long term consequences and is willing to go to trial on your behalf. Contact us or call (503) 227-1233 for your free case consultation.
Learn more about Meteorapathy
There are many medical journal articles about the effects of weather on pain. Here are a few:
Shutty MS, et al. “Pain complaint and the weather: weather sensitivity and symptom complaints in chronic pain patients” Pain, 1992 May;49(2):199-204.
Jamison RN, et al. “Weather changes and pain: perceived influence of local climate on pain complaint in chronic pain patients.” Pain 1995 May;61(2):309-315.
Dixon WG, et al. “How the weather affects the pain of citizen scientists using a smartphone app” NPJ Digit Med. 2019; 2: 105. Published online 2019 Oct 24.
Mazza M, Di Nicola M, Catalano V, Callea A, et al. Description and validation of a questionnaire for the detection of meteoropathy and meteorosensitivity: the METEO-Q. Compr Psychiatry. 2012;53:103–6.
Maini K, Schuster NM. Headache and Barometric Pressure: a Narrative Review. Curr Pain Headache Rep. 2019;23(11):87.
Mirković A, Savić N. Influence of meteorological factors on human health. Sestrinska Vizija. 2022;6:17–21.