Central sensitization can happen because pain creates high levels of activity. If it goes on for too long it can wind-up your nerves making changes to your spinal cord and to your brain. If that happens you can be in constant pain. When the pain is coming from your brain it is called neuropathic pain. It may feel like it is coming from somewhere else in your body. We need to treat where the pain started from (Peripheral) and your brain (Central). This will give a more complete understanding of how to diagnose osteoarthritis completely.
How does Central Sensitization Develop
Acute Pain is your friend
Pain protects your body from damage. If you place your hand on a hot stove you will feel pain and move your hand to stop ongoing damage to your tissues. Damage your tissues anywhere in your body and you will feel pain warning you that damage is happening.
Acute to Chronic Pain.
If your pain lasts for more than three months changes may occur in your body. This is the move from acute to chronic pain. In some people the high state of activity from their damaged tissues can wind-up the receptors in the spine (Dorsal Horn) so that they remain in a state of heightened activity. When signals come in they are increased because of this nervous state and normal touch can feel painful. These signals pass up into the brain and changes can occur in the hippocampus (more) and the Periaqueductal Gray matter. (more) These changes in sensitivity are known as Windup. Your nerves are literally wound up.
Wind-up to Central Sensitization
This is known as central sensitization. Peripheral signals are now increased by changes in the spinal cord and brain and felt as pain. Because the pain is coming from damage in the brain it is called neuropathic pain. The pain from the periphery, eg osteoarthritic knee or low back is called nociceptive pain. Before you had chronic pain you probably had a high pain threshold. You could handle the pain of childbirth. Get knocked about playing sport and not notice it. Now someone bumps you and you are in pain. Your pain threshold is now very low.
“Its All in Your Head?”
Friends and relatives cannot see or feel your pain so they relate your small blow to how they would feel it. Someone bumps them and they hardly notice but when you are bumped it is really bad. They find that hard to understand. They think you are a hypochondriac looking for sympathy. In reality you are suffering and trying to keep it to yourself. They think it is ‘all in your head’ not knowing that it really is in your head as well as in your body. This is central sensitization.
Central Sensitization Syndromes
Anything that causes pain can cause central sensitization if it does not stop after a short time. Once it has sensitized the pain can then spread out into surrounding tissues and gain a life of its own. Because we did not understand what was happening we described new Syndromes by the area they started.
- Fibromyalgia
- Irritable Bowel Syndrome
- Chronic Fatigue Syndrome
- Chronic Headache
- Temporo-Mandibular Disorders
- Pelvic Pain Syndromes
- Primary dysmenorrhea (painful period)
- vulvodynia
- Interstitial cystitis (painful bladder)
- Low Back Pain
- Osteoarthritis
- Myofascial Pain Syndrome
Other Causes of central sensitization
It has now become obvious that central sensitization can follow any excessive stimulation, not just pain.
- post-traumatic stress disorder,
- multiple chemical sensitivity,
- restless leg syndrome .
- over-active bladder
- chronic hives
Excessive stimulation can occur in any of the senses; Vision (bright light), smell (fragrances), sound, skin irritation, bodily sensations and psychological stress.
Headaches and Central Sensitization
Migraine headaches are a classic example. When they start migraine tend to be short lived and tolerable. With time they can become more frequent and more severe. This is often because central sensitization has occurred and they have made the transition from acute to chronic. Close analysis of each headache may reveal that they now have their original headaches alternating with tension type headaches, both in a severe form. They now need to learn when to take migraine tablets and when to take tension headache tablets.
Many chronic illnesses can cause central sensitization. If you have more than one the pain from them all adds up and your brain suffers. It becomes sensitive.
Changes in your brain
Some of the chronic pain that you are feeling is being generated inside your brain. These pain producing locations are accompanied by changes in the function of your brain. Mutso et al [ref] using functional MRI described the changes in hippocampal – cortex connectivity that occur as patients with sub-acute low back pain progress from acute to chronic pain. Yu et al [ref] demonstrated impairments of descending pain modulation in the periaqueductal gray (PAG) of patients with chronic low back pain. Flor et al[ref] measured changes associated with central sensitization in the somatosensory cortex in chronic back pain patients.
Changes in your spinal cord
When central sensitization occurs, the nervous system goes through a process called wind-up and remains in a persistent state of high reactivity. Staud et al [ref], mapped summation mechanisms of dorsal horn neurons (ie, windup) in patients with Fibromyalgia (FM) and determined that central sensitization of FM patients is widespread and similar along the entire spinal neuroaxis, reflecting the widespread nature of the pain that FM patients feel.
Incidence
Nordeman et al[ref] studied 130 female patients with chronic low back pain. Over a third of these women suffered with Widespread Pain (WP) reflecting central sensitization. Their pain and quality of life was significantly worse than those participants who did not have central sensitization.
Central sensitization has been reported in 20% of patients with a knee osteoarthritis.[ref]
Incidence increases with multiple joint involvement. 20% 0f the population have single joint OA and 80% have multiple joint OA. Add Chronic Low Back Pain to your list and your risk of central sensitization rises significantly.
The reported centralized pain in rheumatoid arthritis is estimated to be 62.5%.[ref)
What causes Central Sensitization?
Some people are more at risk than others. Risk factors include trauma, infection, chronic stress, obesity, and depression. Buskila noted a strong family occurrence of fibromyalgia and related conditions suggesting a genetic predisposition for centralized pain syndrome.[ref] Environmental factors may trigger the development of these disorders in genetically predisposed individuals.
Diagnosis of Central Sensitization
Finan et al, found that central sensitization in knee OA is more obvious among patients with reports of high levels of clinical pain in the absence of moderate-to-severe radiographic evidence of pathologic changes of knee OA. [ref] On exam, centralized pain is harder to diagnose if there is swelling, structural changes, abnormal neurological findings, or concern for inflamed joints. In other words if you don’t have physical signs in you knee or hip it is easier to diagnose central sensitization.
To help you decide if you have central sensitization you can try the Central Sensitization Index (CSI) which helps differentiate neuropathic pain. (Ref)
Central Sensitization Treatment
Exercise
Regular mild aerobic exercise alters structures in the central nervous system, (more), 48 and leads to reductions in the pain of many conditions that are mediated by central sensitization. Mild to moderate aerobic exercise is used to treat chronic pain syndromes marked by central sensitization.
Medication
All of this pain is felt as peripheral pain even though some of it is coming from your brain. Treating your primary problem will help one half but you also need to treat the other half, your brain.
This can cause difficulty because increasing treatment of the peripheral pain does not help the central sensitization component of the pain. Inflammatory markers will be lower but pain and Quality of Life is poor, until you treat the central pain.
Antidepressants and anticonvulsants can be useful for central pain. NSAIDs and opioids can help with peripheral pain. (more)
Joint Replacement Surgery
If you have Osteoarthritis and need joint replacement surgery you will be treating the peripheral problem. Good surgeons in good facilities treating single joint disease in healthy individuals can achieve up to a 90%[more] success rate. 10 to 15% of patients with single joint disease will have central sensitization.
If you have multiple joint OA your risk of central sensitization increases. If you also have chronic low back pain the incidence further increases. Add in any other comorbidity such as diabetes, SLE, Sjogren’s, IBS, Crohn’s, etc, and your risk of central sensitization is very high.
Hawker et al, studied a group of 202 patients in Ontario, Canada who had total hip or knee surgery. 80% of patients had multiple joint involvement and more than half had Chronic Low Back Pain.
Successful outcomes were defined as anyone getting an improvement of more than half a standard deviation (SD) in the global WOMAC score ( a clinically important difference – CID). To verify these results they also recorded the patients achieving the Patient Acceptable Symptom State (PASS).12
Only 53% of subjects met this threshold.
Patients with osteoarthritis and centralized pain report less benefit following joint replacement surgery. (Ref) This is an example of treating half the problem (the joint) and not treating central sensitization (the brain).
Girbes et al concluded “the scientific literature offers scant information addressing the treatment of central sensitization, specifically in patients with osteoarthritis. Interventions such as cognitive-behavioral therapy and neuroscience education potentially target cognitive-emotional sensitization (and descending facilitation), and centrally acting drugs and exercise therapy can improve endogenous analgesia (descending inhibition) in patients with osteoarthritis. Future studies should assess these new treatment avenues.” (Ref)
Adipose derived Stromal Cells treat Central Sensitization
Adipose derived Stromal Cells have shown promise for the treatment of central sensitization in osteoarthritis patients and needs further investigation.