What is Fibromyalgia?

Fibromyalgia is a chronic neurological disorder characterized by widespread pain, profound fatigue, non-restorative sleep, and cognitive dysfunction (often called “fibro fog”) [1]. Rather than a primary disease of joint cartilage, structural bone tissue, or peripheral muscles, fibromyalgia is scientifically recognized as a disorder of altered central pain processing within the central nervous system (CNS) [2]. The brain and spinal cord process sensory signals abnormally, amplifying routine neural inputs into widespread pain [2, 3].

The Paradigm Shift: Understanding Nociplastic Pain

For decades, medical literature mischaracterized fibromyalgia as a “musculoskeletal” condition. Modern pain science has evolved beyond this classification. In 2017, the International Association for the Study of Pain (IASP) officially introduced a third mechanistic descriptor for chronic pain: nociplastic pain [4]. Pain taxonomy is divided into three distinct categories:

1. Nociceptive Pain: Pain arising from actual or threatened damage to non-neural tissue (e.g., bone fracture, osteoarthritis, sprains) [4].
2. Neuropathic Pain: Pain caused by a demonstrable lesion or disease of the somatosensory nervous system (e.g., diabetic neuropathy, sciatica, shingles) [4].
3. Nociplastic Pain: Pain that arises from altered nociception despite no clear evidence of actual tissue damage or structural nerve lesions [4]. Fibromyalgia is the prototype condition for nociplastic pain [1, 4].

Central Sensitization: The Underlying Mechanism

While “nociplastic pain” describes the clinical category, central sensitization is the physiological mechanism driving it [3, 4]. In a healthy nervous system, pain signal transmission dynamically adjusts in response to tissue injury, inflammation, or threat. In someone living with fibromyalgia, central pain pathways remain persistently hyper-reactive [2, 3]. This altered central processing manifests as two key sensory phenomena:

• Hyperalgesia: An exaggerated pain response to stimuli that would normally cause only mild discomfort (such as a light bump or firm pressure) [3].
• Allodynia: Experiencing pain from stimuli that are ordinarily non-painful, such as light clothing touching the skin, gentle touch, or subtle temperature changes [3].

Cerebrospinal fluid and neuroimaging studies confirm that central sensitization involves elevated levels of excitatory neurotransmitters (Substance P and glutamate) combined with impaired descending inhibitory pathways mediated by serotonin and norepinephrine [2, 5].

The Evolution of Diagnostic Criteria

Diagnostic methods for fibromyalgia have shifted significantly over the past three decades to reflect better clinical reality. We’ve outlined the most notable updates. 

1. The 1990 ACR Criteria & Phasing Out “Tender Points”.

The 1990 American College of Rheumatology (ACR) criteria required pressing on 18 specific physical “tender points” across the body, requiring pain in at least 11 points alongside widespread pain [6]. Tender point testing had major clinical limitations, with counts varied based on practitioner technique, ignored essential non-pain symptoms like fatigue and cognitive issues, and reinforced the incorrect assumption that fibromyalgia was a peripheral soft-tissue disorder [1, 6].

2. The ACR 2010 & 2016 Criteria Revisions

To replace tender point exams, the ACR developed symptom-based diagnostic tools in 2010 and refined them in 2016 [1, 7]:

• Widespread Pain Index (WPI): A score (0–19) evaluating pain distribution across 19 body regions over the preceding 7 to 14 days [1].
• Generalized Pain Requirement (2016 Update): Pain must be present in at least 4 of 5 defined regions (left upper, right upper, left lower, right lower, and axial) to prevent regional pain conditions from being misdiagnosed as fibromyalgia [1].
• Symptom Severity Scale (SSS): A score (0–12) quantifying the severity of fatigue, unrefreshing sleep, cognitive dysfunction, and somatic symptoms [1, 7].

3. Current Scoring Thresholds

A patient meets the clinical case definition for fibromyalgia if: WPI ≥ 7 AND SSS score ≥ 5 OR WPI 4–6 AND SSS score ≥ 9 [1]. Generalized pain is present in at least 4 of 5 body regions [1]. Symptoms have persisted at a consistent level for at least 3 months [1, 7].

No Longer a “Diagnosis of Exclusion”

A major milestone of the 2010 and 2016 ACR revisions was the explicit removal of diagnostic exclusions: Fibromyalgia is no longer a diagnosis of exclusion [1, 7]. Under older medical models, clinicians attempted to rule out every possible medical illness before considering fibromyalgia. Research confirms that fibromyalgia frequently co-exists alongside other conditions [1, 2].

A patient can be validly diagnosed with fibromyalgia even if they also have other conditions like Autoimmune diseases (Rheumatoid Arthritis, Systemic Lupus Erythematosus, Sjögren’s Syndrome), Endocrine disorders (Hashimoto’s Thyroiditis, Hypothyroidism), Small Fiber Neuropathy (SFN), Dysautonomia / Postural Orthostatic Tachycardia Syndrome (POTS), and Irritable Bowel Syndrome (IBS) [9].

Clinicians do not need to run endless tests to rule out every alternative diagnosis before treating fibromyalgia. Both primary and co-occurring conditions can be identified and managed simultaneously [1].

Next Steps After Diagnosis

Receiving a diagnosis shifts the focus to targeted management. Conventional therapies focus on modulating central sensitization through pharmacologic interventions, while functional medicine evaluates systemic drivers such as gut microbiome health, mitochondrial energy deficits, and neuroinflammation.