New Pain Mechanisms Revealed

Neuropathic pain is a chronic pain condition caused by a damaged or dysfunctional nervous system. It is characterised by shooting and burning pain that lasts long after the initial onset. Common causes of neuropathic pain include:

• alcoholism
• amputation
• back, leg and hip problems
• chemotherapy
• diabetes
• facial nerve problems
• HIV or AIDS
• multiple sclerosis
• shingles
• spine surgery

Unfortunately neuropathic pain doesn’t respond much to conventional analgesics but instead, antidepressants (amitriptyline and duloxetine) and anticonvulsants (gabapentin and pregabalin) have been found to help relieve pain.

A new study published in this month’s edition of Neuron by Thomas Nevian et al from the Department of Physiology at the University of Bern has revealed some of the mechanisms involved in neuropathic pain. In a mouse model, they found that neurons in the gyrus cinguli, a part of the brain found in the limbic system (usually associated with emotion) are modified by pain forming a “pain memory”. Neurons in the gyrus cinguli become more excitable due to a down-regulated ion channel. This leads to an increased number of nerve impulses which the brain perceives as pain.

The researchers managed to restore the function of the ion channel by activating a receptor sensitive to serotonin. This explains the success of some antidepressants in treating neuropathic pain. Nevian et al were able to identify the specific subtype of serotonin receptor that was more efficient at reducing the perception of pain. Excitingly, this could lead to the development of more effective drugs to treat neuropathic pain.

Meditation Decreases Chronic Neck Pain

A group of German researchers recently published the results of a study looking into the benefits of meditation on people with chronic neck pain. The article was published in The Journal of Pain. They studied about 90 people who had neck pain for an average of 11 years. The average age of the participants was 50 years. Their results found significant improvements in pain reduction and pain coping but no effect on functional disability.

The findings suggest that meditation could be used as an adjunct alongside physical treatments that provide functional benefits.

What Triggers Low Back Pain?

A study published this month in Arthritis Care and Research by Daniel Steffens et al. from the University of Sydney has looked at the risk factors that could lead to acute low back pain. Acute low back pain is back pain that comes on suddenly and resolves after a few days or weeks as opposed to chronic low back pain which is long-standing.

They surveyed close to 1000 people and asked them about the presence of 12 physical and psychosocial factors up to 4 days before the onset of back pain. The results revealed that a number of triggers were linked to acute low back pain:

• moderate to vigorous physical activity increased the risk by 3
• manual tasks involving awkward postures increased the risk by 8
• being distracted during an activity increased the risk by 25
• age decreased the effect of exposure to heavy loads
• risk was highest between 7 am and mid-day

Over the years, I’ve noticed that the parents of young children have an increased incidence of low back pain. Having seen some of the risk factors high-lighted in this study, it becomes evident how sleep-deprived, fatigued and distracted parents that often lift their children in awkward positions can dramatically increase the risk of low back pain. It’s also interesting to note that distraction seems to massively increase the risk of low back pain and therefore underlines the importance of mindfulness.

Diabetes Linked To Shoulder & Hand Pain and Disability

A recent study by Shah et al. found that about two-thirds of patients attending a diabetes outpatient clinic reported shoulder pain and/or disability. They had significant restrictions in shoulder movement, decreased shoulder strength and hand grip strength. In addition to this, they had a greater likelihood of decreased sensation and limited mobility of the hand. Further research is needed to understand the underlying mechanisms and to find preventative measures.

Acupunture Mechanisms Revealed

Research on mice by da Silva et al has revealed new mechanisms underpinning the workings of acupuncture. They injected carrageenan into the calf muscles of mice. This created an inflammatory response with associated pain and swelling. Manual acupuncture of Spleen 6 (an acupuncture point in the lower leg) reduced pain, heat and swelling of the muscle. Repeated acupuncture of Spleen 6 produced a phenotypic change from pro-inflammatory cells (M1 macrophages) to anti-inflammatory cells (M2 macrophages) with an associated increase in interleukin-10 concentrations in muscle which led to reduced pain and inflammation.

The Brain Can Learn To Decrease Pain

New research led by Raymonde Scheuren from the University of Luxembourg has brought some new insights into the world of pain. It’s generally known that a pain present in one part of the body can be attenuated by painfully stimulating a different part of the body. This is known as diffuse noxious inhibitory control (DNIC) and is thought to take place to allow the body to focus on the new, and potentially more important, threat to the body.

In their experiments, Scheuren et al. caused pain in subjects by electrically stimulating a foot. They then created a second source of pain by placing the opposite hand in a bucket of ice-cold water. As predicted, after the hand was immersed in cold water, the pain from the foot decreased. The interesting part of the experiment was when the insertion of the hand into cold water was repeatedly coupled with a phone ring tone. Afterwards, simply playing the ring tone (without placing a hand in cold water) was enough to decrease foot pain from the electrical stimulation! Conditioning had taken place. Conditioning is a form of learning where the physiological effect of a stimulus (ice-cold water) is reproduced by an unrelated stimulus (phone ring tone) by having the two repeatedly happen simultaneously. The one takes on the effect of the other.

The reverse effect possibly plays a part in chronic pain. Sights, sounds, smells and other sensations that were present during the traumatic incident that caused the injury can unconsciously become triggers for pain long after the injury has healed.

Vitamin D Deficiency Linked To Chronic Pain

Paul McCabe et al from the University of Manchester analysed data from the European Male Ageing Study and found that men with vitamin D deficiency at the start of the study were more than twice as likely to experience ongoing widespread pain over the next 4 years as those with high levels of vitamin D. It was noted that the men with chronic widespread pain were more likely to be physically active, obese, depressed and to have other health problems. Once these other factors were taken into account the link between vitamin D and pain disappeared.

However, John McBeth et al analysed data from the same study and found that even after adjusting for other health factors, pain remained moderately associated with increased odds of having low vitamin D levels. This is supported by a 5-year longitudinal study published last year by Laura Laslett et al in which vitamin D deficiency was found to predict incidence or worsening of knee pain and hip pain.

There seems to be a link between a deficiency of vitamin D and pain but could supplementation with vitamin D help to decrease pain? Between 2008 and 2010, Shreuder et al conducted a study in Holland and they did indeed find a small positive benefit (less pain and better function) after taking a high dose of vitamin D for 6 weeks.

What could the mechanism behind vitamin D and pain be? Tague et al found that vitamin D deficiency in rats can lead to a hyperinnervation of skeletal muscle which is likely to contribute to muscle hypersensitivity and pain.

Vitamin D is naturally present in a few dietary sources such as fish oils, mushrooms, eggs and liver. Other than supplements, sunlight exposure is the best source of vitamin D for most of people.

Potential Advances In The Treatment Of Osteoarthritic Pain

In a recent study published in Annals of the Rheumatic Diseases and reported in Medical News Today, Sara Kelly and colleagues from the Arthritis Research UK Pain Centre at The University of Nottingham have discovered a new way to possibly decrease the chronic pain affecting people with osteoarthritis. They studied a protein receptor called TRPV1 which is present in the synovial membranes of joints. These receptors are responsive to pain. Injecting TRPV1 agonists directly into the joint produced pain relieving effects.

The study was performed on rats so before being used on humans the results will need to be replicated in clinical trials and monitored for potential side effects.

Until then the best self-help advice for those with osteoarthritis is weight loss (if it affects joints in the lower limbs), stretching & strengthening exercises and maintaining moderate levels of activity. Nutritional supplements can also help (see related articles here).

Poor Sleep Linked To Pain

A new study by Arthritis Research UK Primary Care Centre at Keele University and published in Arthritis & Rheumatology has identified factors associated with an increased risk of developing widespread pain in adults over 50. Of the factors measured, non-restorative sleep was the strongest independent predictor of new onset widespread pain.

Stress Management Could Help Decrease Pain

A recent study by Dr. Pierre Rainville and Étienne Vachon-Presseau from the University of Montreal has shed some light on the relationships between stress, the brain and pain. Their study compared 16 patients with chronic back pain with a control group of 18 healthy subjects. They found that back pain patients had higher levels of cortisol than subjects from the control group. Cortisol is produced by the adrenal glands and is secreted in response to stress. It’s a steroid hormone that increases blood sugar levels, suppresses the immune system, and may decrease bone formation; so an excess, particularly when maintained over a long period, is detrimental to health. The higher cortisol levels were associated with smaller hippocampal volumes. The hippocampus is a part of the brain that is involved in learning, memory and regulation of emotion. People with depression and post-traumatic stress disorder have been found to have hippocampal atrophy. The subjects with chronic back pain had stronger responses to pain stimuli in a brain region involved in anticipatory anxiety in relation to pain. Brain activity in response to the painful stimulus partly reflected the intensity of the patient’s current clinical pain condition.

The findings can be summarised in the following flow chart.

The authors suggest that stress management techniques such as relaxation and meditation should be used to complement medical treatments in patients with pain. They believe this can help to decrease the impact of pain and perhaps even prevent chronicity.