The Biology & Overlapping Conditions

In previous pages, we discussed that nociplastic pain is a change in how the nervous system processes signals. To understand why this happens, we have to look at the biology of the brain and spinal cord. The primary neurophysiological process linked to nociplastic pain is called central sensitization ^[1][2].

The ‘Broken Volume Knob’ Analogy

Think of your nervous system like a radio. In a healthy system, the volume knob is adjusted based on the signal. If you touch a hot stove, the volume spikes so you pull your hand away; when the stove is off, the volume stays low.

In central sensitization, the “volume knob” in your brain and spinal cord becomes stuck on high ^[3]. This simplified model involves two main biological changes:

1. Amplified Signaling (Excitatory Gain): The nerve cells responsible for sending pain signals to the brain become hyper-excitable. They fire more easily, stay active longer, and respond to signals that aren’t even painful (like a light breeze) ^[1][4].
2. Impaired Inhibition (Loss of Filtration): Your body has a natural “pain-filtering” system that uses chemicals like serotonin and norepinephrine to dampen or block unnecessary signals. In central sensitization, this system is weakened. The brain loses its ability to “mute” the background noise, leaving you flooded with sensory information ^[1][5].

Chronic Overlapping Pain Conditions (COPCs)

Because central sensitization happens in the central nervous system (the “main computer”), symptoms often appear in different parts of the body at the same time. The National Institutes of Health (NIH) recognizes a group of 10 Chronic Overlapping Pain Conditions (COPCs) that frequently occur together because they may share some of this underlying biology ^[6][7].

The 10 recognized COPCs are:

• Fibromyalgia: The prototypical nociplastic condition, involving widespread pain and fatigue ^[6].
• Irritable Bowel Syndrome (IBS): Pain and digestive changes without visible damage to the gut ^[6].
• Temporomandibular Disorders (TMD/TMJ): Pain in the jaw joints and muscles ^[6].
• Chronic Low Back Pain: Specifically back pain that persists without a clear structural cause ^[6].
• Chronic Migraine: Recurrent, severe headaches ^[6].
• Chronic Tension-Type Headache: Persistent, dull head pain ^[6].
• Endometriosis: A condition where tissue similar to the lining of the uterus grows outside it, often involving central amplification of pain ^[6].
• Interstitial Cystitis/Bladder Pain Syndrome: Chronic bladder pressure and pain ^[6].
• Vulvodynia: Chronic pain in the area around the opening of the vagina ^[6].
• Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): Severe, persistent fatigue and “post-exertional malaise” ^[6].

Shared Vulnerability, Distinct Diagnoses

While these conditions are grouped together, they are not simply different symptoms of one single issue. They are conditions that may share some mechanisms, but each remains a distinct medical diagnosis that requires its own investigation and treatment. For example, endometriosis can involve peripheral lesions and inflammation, and ME/CFS has distinctive post-exertional malaise that requires specialized energy management.

Understanding this shared biology is empowering—it means that treatments supporting the central nervous system may help across multiple conditions simultaneously. However, each condition is real on its own and may require its own specific medical care ^[6][5].