Fibromyalgia (FM) is a chronic disorder that causes widespread pain throughout the body. This pain is often accompanied by profound fatigue, sleep disturbances, and cognitive difficulties, frequently described as “fibro fog.” A common frustration is that the pain is invisible; standard medical imaging like X-rays or MRIs show no signs of tissue damage or inflammation. The concept of “tender points” emerged as a historical attempt to quantify this otherwise subjective experience.
The Historical Role of Tender Points in Diagnosis
Tender points (TPs) are highly specific, localized areas on the body that were used for decades as a primary tool for classifying and diagnosing fibromyalgia. These points are not swollen or inflamed, but they elicit a sharp, reproducible pain when pressed by a clinician. The American College of Rheumatology (ACR) established the 1990 criteria, defining diagnosis by combining chronic widespread pain with tenderness in a minimum number of these points.
A patient had to report pain in 11 out of 18 designated sites symmetrically distributed across the body. The examination required the doctor to apply a consistent force, about 4 kilograms per square centimeter. These paired points were located near muscle attachments in areas such as the lower neck, upper chest, elbows, knees, buttocks, and shoulders. This standardized physical examination provided a quantifiable metric for a condition otherwise defined by a patient’s report of symptoms.
Why Diagnostic Criteria Shifted
The reliance on tender points faced increasing criticism because the test proved subjective and failed to capture the full picture of the disorder. A patient’s pain threshold varies significantly based on factors like mood or the examiner’s technique, making results inconsistent between clinicians. Furthermore, the 1990 criteria focused almost exclusively on the physical sensation of pain, overlooking other major symptoms of FM.
The diagnosis did not account for debilitating fatigue, unrefreshing sleep, or cognitive dysfunction. To address these limitations, the ACR updated the criteria in 2010 and again in 2016, moving away from the physical examination of tender points. The modern diagnostic approach now uses the Widespread Pain Index (WPI) and the Symptom Severity Scale (SSS). The WPI scores the number of painful regions out of 19 defined areas, while the SSS measures the severity of non-pain symptoms, providing a broader profile for diagnosis.
Understanding the Invisible Pain
Central Sensitization
While standard MRI or X-ray scans may show physically normal tissue, researchers are now using advanced neuroimaging to gain insight into the origin of FM pain. The most significant finding is central sensitization, which explains why the pain feels real without a visible peripheral cause. In central sensitization, the central nervous system remains in a persistent state of high reactivity, essentially turning up the volume on all sensory signals.
This heightened state means that normal, non-painful sensations are amplified and processed by the brain as painful, a phenomenon known as allodynia. Functional MRI (fMRI) studies show that when a pain stimulus is applied, individuals with FM exhibit a higher activation pattern in the brain’s pain matrix compared to healthy individuals. This difference in brain activity offers a scientific visualization of the altered pain processing.
Tender Points vs. Trigger Points
It is important to distinguish the historical “tender points” from “trigger points,” which are often confused. Trigger points are hyperirritable spots found within a taut band of skeletal muscle that, when pressed, can cause pain to radiate to a distant part of the body, a characteristic seen in Myofascial Pain Syndrome. Tender points, by contrast, cause only localized pain at the site of pressure. This localized pain reflects a generalized, systemic hypersensitivity associated with central sensitization, not a specific muscle knot. The current scientific focus confirms that the pain in FM is a disorder of pain processing, which is why the discomfort is felt throughout the body but cannot be seen on conventional medical images.