The Volume Knob Is Not in the Knee | The Pained Brain, Chapter 9

Central sensitization symptoms

Central Sensitization Symptoms: What Your Numbers Can Show

Central sensitization symptoms include ordinary touch that hurts, pain that grows sharper with each repeated tap, and pain in places that were never injured. X-rays and CRP read normal, but body composition, blood work, heart rate variability and sudomotor testing show the terrain that turns the pain up.

When everything hurts and every test comes back normal, the problem may be the volume setting of the nervous system. That setting leaves traces in the body you can actually measure.

Central sensitization symptoms are easy to describe and hard to prove at a routine appointment: pain that spreads to places that were never hurt, a light touch that stings, an ache that grows sharper every time it repeats. The X-ray and blood work look fine, and someone suggests the pain is exaggerated.

The video above, The Volume Knob Is Not in the Knee, is Chapter 9 of The Pained Brain by Dr. Gurpreet Singh Padda, MD, MBA, MHP, and Dr. KrisJay Fucanan, MD. It explains how the nervous system becomes an amplifier. What follows is the measurement side: what a normal result actually ruled out, and what can be put on paper instead.

What does central sensitization feel like?

Your spinal cord and brain decide how loud each pain signal gets. After months of steady input from a worn joint or an irritated nerve, the relay station in the cord can learn to turn every signal up. Researchers describe the result as a lasting rise in how excitable those pathways are, one that outlives the injury and yet can reverse. It is a state the nervous system has learned, not permanent damage.

The symptoms follow from that. Ordinary touch registers as pain, which doctors call allodynia. A repeated tap hurts more with each repetition. Pain shows up on the opposite side of the body, or in the neck and jaw, where nothing is wrong. It is common, too. Pooled across sixteen studies of 2,347 people with chronic low back pain, 43.2 percent scored at or above the usual cutoff on a sensitization questionnaire.

Why do my tests come back normal when everything hurts?

A typical workup looks for damage where it hurts: a picture of the joint or spine, a CRP blood test for inflammation, a weight and a BMI. Every one of those can be normal in a person whose nervous system is running hot.

The image shows structure, not the volume setting. A replaced knee can look perfect on film while the pain carries on.
The CRP reads the bloodstream. In a study of 160 people, patients with disc disease or a herniated disc had 34 inflammatory proteins raised in their spinal fluid, while those same patients’ blood proteins ran lower than the controls’ did.
The BMI counts total weight. Among 265 adults with knee pain, low pain thresholds went with more visceral fat, the fat packed around the organs, and more leptin, a hormone that fat releases. Both links held even when BMI was normal, and CRP, fasting glucose and HbA1c were not linked to the low thresholds at all.

The amplifier itself is tested with pain-clinic tools such as a pressure algometer, a calibrated gauge pressed on skin far from the sore spot. That is quantitative sensory testing, a different test done elsewhere. Measura [Cardiometabolic and Autonomic Health Analysis] measures the terrain around the amplifier: the body composition, metabolic, autonomic and nerve findings that research ties to a lowered pain threshold. You can read more about that link on chronic pain and metabolic health.

What can be measured when you have central sensitization?

Dr. Padda’s position is that metabolic dysfunction and inflammation physically sensitize the nerves.

Bioimpedance body composition separates fat from muscle, so a normal weight cannot hide a heavy fat load. In 72 adults with no pain condition, the obese group’s pressure pain threshold averaged 620.72 kilopascals against 1,154.70 in the normal-weight group.
Laboratory panels reach past CRP to the metabolic markers your physician chooses to order. Because CRP missed what the fat measurement caught in the knee-pain study, a normal CRP should not end the search.
Heart rate variability reflects how the autonomic nervous system is balancing. In 302 healthy adults with no pain condition, a combined cardiometabolic load built from body mass, blood pressure and heart rate variability went with stronger spinal facilitation and weaker spinal inhibition on reflex testing, before any of them hurt.
Sudomotor testing looks at sweat-gland function, which is run by the small nerve fibers of the hands and feet. In fibromyalgia, pooled studies find small-fiber pathology in 49 percent of patients.

That figure comes from skin biopsy, a separate test; sudomotor testing does not diagnose fibromyalgia, but it looks at the same class of small nerve fibers. One caution: among 57 fibromyalgia patients, those with and without fiber loss tested the same on sensory measures. The fiber finding is residue of a body inflamed for years, not the explanation for the pain.

Can being disbelieved make pain worse?

The third driver is not biological. A person told the pain is invented carries a stressor on top of the pain. Across nineteen studies, the stigma pain patients perceive tracked their pain intensity, disability and depression. Dismissal by relatives independently raised the odds of the fibromyalgia phenotype 1.81-fold. And the malingering rates still quoted at patients come from neuropsychologists’ impressions of legal cases, not from measurements.

Here is the part most people miss. A number in your chart does social work as well as medical work. The next clinician who opens the record reads a documented visceral fat load or an abnormal sudomotor result very differently from a note that says widespread pain, cause unclear.

There is a longer-range reason as well. Among 188,594 British adults followed for thirteen years, chronic widespread pain carried 2.55 times the hazard of mild cognitive impairment. The researchers’ genetic analysis did not confirm cause, so read it as a warning light. A baseline cognitive assessment gives you something to compare against later.

How do you calm down central sensitization?

The humility in this story belongs to pain medicine. The specialty built its tools for the joint, and in many people the problem had already moved into the spinal cord while the needles kept pointing at the knee. The encouraging side is that the amplifier is kept running by input and by terrain, and both can change.

When 110 adults with excess body fat lost 7.9 percent of their body mass by diet over three months, the share living with chronic musculoskeletal pain dropped from 51 percent to 25 percent. Nobody treated a joint. There was no control group, so treat it as a strong signal from a weak design. Their hsCRP did not change, which is exactly why body composition rather than BMI is the number worth following over time.

Food, sleep and movement act on that fuel. Exercise needs care, because the natural pain relief a workout gives a healthy person is not reliably present in someone with chronic pain, so it is best built up gradually with your clinician. Any decision about medication stays with your own physician.

What to ask for at your next visit

Can we measure my body composition, not just my weight and BMI?
My CRP was normal. Which metabolic markers have not been checked yet?
Given how widespread my pain is, would sudomotor or heart rate variability testing add anything?
Could my pain threshold be tested on a spot away from the pain, more than once?
Can we record a cognitive baseline now?

The book’s companion to Chapter 9 lays out every study behind these numbers, with its limits, and it is written to hand to your doctor. When that same pain drives someone to an emergency room in the middle of the night, what the ER checks and what it leaves unmeasured is the next piece.

Frequently asked questions

What are the most common central sensitization symptoms?

Pain that spreads past the original injury, ordinary touch that hurts, pain that sharpens when a stimulus repeats, and tenderness where nothing is injured. Many people carry more than one pain condition at once; among 149,742 rheumatology patients, 22.7 percent had several overlapping ones. Symptoms point toward the amplifier, and measurements can show the terrain feeding it. Bring these questions to your doctor.

Can a blood test diagnose central sensitization?

No single blood test does. In people with disc pain, inflammatory proteins were high in spinal fluid while blood levels ran below controls, and in adults with knee pain, CRP was not tied to low pain thresholds. Laboratory panels still matter for the metabolic side of the picture, read together with body composition. Learn what a test result can and cannot tell you.

Is sudomotor testing the same as a skin biopsy?

No. A skin biopsy removes a small tissue sample to count nerve fibers and is done elsewhere. Sudomotor testing is noninvasive and measures sweat-gland function controlled by small nerve fibers in the hands and feet. It does not diagnose fibromyalgia or central sensitization; your physician interprets the result alongside your history. Read what sudomotor dysfunction means.

Why would body composition matter if my weight is normal?

Because where fat sits matters more than what the scale says. In adults with knee pain, visceral fat and leptin were linked to widespread pain even among those with a normal BMI, a thin-outside, inflamed-inside pattern. Bioimpedance separates fat from muscle, so that pattern does not hide behind a healthy weight. See why body composition is not the same as weight.

Does Measura treat central sensitization?

No. Measura is a testing service. It measures metabolic, vascular, autonomic, nerve and cognitive markers and sends the findings to your physician, who decides what they mean for your care. Central sensitization itself is assessed with pain-clinic sensory testing, and these measurements describe the terrain around it. Understand how your results are reported.

What triggers central sensitization?

Months of steady pain signals from a worn joint or an irritated nerve can teach the relay station in the spinal cord to turn every signal up. Dr. Padda’s position is that metabolic dysfunction and inflammation physically sensitize the nerves, which is why fat load, blood markers and autonomic balance matter. Being told the pain is invented adds a stressor on top, and that stigma tracks with pain intensity and disability.

Is central sensitization permanent?

No. Researchers describe it as a lasting rise in how excitable the pain pathways are, one that can outlive the injury and yet can reverse. It is a state the nervous system has learned, not permanent damage. The amplifier is kept running by input and by terrain, and both can change, which is why body composition is the number worth following over time.

How is central sensitization diagnosed?

The amplifier itself is tested in a pain clinic with quantitative sensory testing, such as a pressure algometer pressed on skin far from the sore spot. Studies also use a sensitization questionnaire with a set cutoff. X-rays and CRP often read normal. Measura does not diagnose central sensitization; it measures the terrain around it and sends the findings to your physician.

Put the Terrain on Paper

If your pain has spread and your tests keep coming back normal, ask for the measurements that show body composition, metabolic markers, autonomic balance and small-nerve function. Your results go to your physician.

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References

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