Fibromyalgia Causes: What Triggers Central Sensitization and Why Some People Are More Vulnerable

Fibromyalgia Is Not “Just Pain”

For decades, fibromyalgia was dismissed as psychosomatic, a wastebasket diagnosis for patients whose pain couldn’t be explained by standard testing. That view has been thoroughly dismantled by two decades of neuroscience, immunology, and genetics research. Fibromyalgia is a disorder of pain processing with measurable biological underpinnings. The question is no longer whether it’s real, but rather how the nervous system gets locked into this state and why it happens to some people and not others.

The short answer: there is no single cause. Fibromyalgia arises when a genetically susceptible nervous system encounters a triggering event, or an accumulation of events, that pushes pain processing circuits into a self-reinforcing state of hyperexcitability. Understanding these components matters because it points toward more targeted and effective treatment strategies.

Central Sensitization: The Core Mechanism

Central sensitization is the neurological process at the heart of fibromyalgia. In a normally functioning nervous system, pain signals from the body are processed, modulated, and filtered. Not every signal makes it to conscious awareness, and the brain adjusts the “volume” of incoming pain signals based on context [1].

In central sensitization, this modulation system breaks down in two ways:

• Amplified excitation: The spinal cord and brain become hyperexcitable, magnifying incoming pain signals. Stimuli that normally register as mild pressure or temperature now register as pain (allodynia). Stimuli that are mildly painful become severely painful (hyperalgesia).
• Impaired inhibition: The descending pain inhibitory pathways, which normally dampen pain signals, become less effective. Think of it as losing the brakes on a car that’s simultaneously hitting the accelerator.

Functional MRI studies show that fibromyalgia patients have increased activation in brain regions that process pain (the insula, anterior cingulate cortex, and somatosensory cortex) when exposed to stimuli that healthy controls find non-painful. This isn’t imagined pain. It’s documented, measurable neural hyperactivity [2].

The neurotransmitter picture supports this model. Fibromyalgia patients have elevated levels of excitatory neurotransmitters like glutamate and substance P in their cerebrospinal fluid, and reduced levels of inhibitory neurotransmitters like serotonin, norepinephrine, and GABA. This neurochemical imbalance directly explains why SNRIs (which boost serotonin and norepinephrine) and pregabalin (which reduces excitatory neurotransmitter release) are effective treatments for some patients [3].

Genetic Vulnerability

Fibromyalgia runs in families. First-degree relatives of fibromyalgia patients are 8 times more likely to develop the condition than the general population. Twin studies estimate that genetic factors account for approximately 50% of the risk, with environmental factors accounting for the other half [4].

The genetic landscape is not a single “fibromyalgia gene” but rather a collection of polymorphisms that affect pain processing, stress response, and neurotransmitter metabolism:

• COMT (catechol-O-methyltransferase): The Val158Met polymorphism reduces the enzyme’s ability to break down catecholamines (dopamine, norepinephrine, epinephrine). The low-activity “Met” variant is associated with higher pain sensitivity and increased fibromyalgia risk [5].
• Serotonin transporter gene (SLC6A4): The short allele of the 5-HTTLPR polymorphism reduces serotonin reuptake efficiency and is more common in fibromyalgia patients.
• SCN9A: This gene encodes a sodium channel (Nav1.7) critical for pain signaling. Variants in SCN9A are associated with altered pain sensitivity across multiple chronic pain conditions, including fibromyalgia [6].
• HLA associations: Some studies have found increased prevalence of certain HLA (human leukocyte antigen) types in fibromyalgia, hinting at an immune-genetic component.

What this means practically: you don’t inherit fibromyalgia itself. You inherit a nervous system that’s more susceptible to developing central sensitization when exposed to the right (or wrong) triggers. This is why two people can experience the same car accident and one develops widespread chronic pain while the other recovers fully.

Triggering Events

Most fibromyalgia patients can identify a precipitating event or period that preceded symptom onset. The most commonly identified triggers include:

Physical Trauma

Motor vehicle accidents, surgeries, and physical injuries are among the most frequently reported triggers. A prospective study found that individuals who experienced whiplash injuries were 10 times more likely to develop widespread pain within 12 months compared to controls who experienced leg fractures [7]. The hypothesis is that the combination of tissue injury, pain signaling, inflammatory mediators, and psychological distress creates a “perfect storm” that tips a vulnerable nervous system into central sensitization.

Infections

Several infections have been linked to fibromyalgia onset:

• Epstein-Barr virus (EBV): The virus that causes mononucleosis. Post-infectious fatigue and pain syndromes following EBV are well-documented, and some progress to meet full fibromyalgia criteria [8].
• Lyme disease: Post-treatment Lyme disease syndrome shares significant symptom overlap with fibromyalgia, and some patients initially diagnosed with PTLDS eventually receive a fibromyalgia diagnosis.
• Hepatitis C: Chronic hepatitis C infection is associated with a significantly elevated risk of fibromyalgia, possibly through direct effects on the nervous system or chronic immune activation.
• COVID-19: Long COVID has emerged as a significant trigger for new-onset fibromyalgia. Studies report that 30-40% of long COVID patients meet fibromyalgia diagnostic criteria, suggesting that SARS-CoV-2 can trigger central sensitization through neuroinflammatory mechanisms [9].

The common thread is that acute infection triggers a cascade of inflammatory cytokines, microglial activation, and immune dysregulation that, in a genetically susceptible individual, doesn’t fully resolve after the infection clears.

Psychological Trauma and Chronic Stress

Adverse childhood experiences (ACEs), post-traumatic stress disorder (PTSD), and chronic psychological stress are strongly associated with fibromyalgia. A meta-analysis found that individuals who experienced childhood physical or sexual abuse had a 2-3 fold increased risk of developing fibromyalgia in adulthood [10].

The mechanism isn’t purely psychological. Chronic stress and trauma produce measurable changes in the hypothalamic-pituitary-adrenal (HPA) axis, autonomic nervous system, and central pain processing. Prolonged cortisol dysregulation alters neuroplasticity and immune function in ways that prime the nervous system for central sensitization. The brain’s threat detection system, already calibrated to high alert by trauma, begins interpreting normal sensory input as dangerous, including pain signals.

Hormonal Transitions

Fibromyalgia is 2-3 times more common in women than men, and many female patients report symptom onset during hormonal transition periods: puberty, postpartum, perimenopause, or after hysterectomy. Estrogen has modulatory effects on pain processing, serotonin synthesis, and microglial activation. Declining or fluctuating estrogen levels may reduce the nervous system’s pain inhibition capacity, lowering the threshold for central sensitization [11].

Neuroinflammation: The Immune-Brain Connection

One of the most significant advances in fibromyalgia research has been the recognition that neuroinflammation plays a central role. Microglia, the immune cells of the central nervous system, are activated in fibromyalgia patients.

A landmark 2019 PET imaging study using a radiotracer that binds to activated microglia demonstrated widespread neuroinflammation in fibromyalgia patients compared to healthy controls. The degree of microglial activation correlated with fatigue severity [12]. This finding bridged a gap in the field. Central sensitization had been well-established, but the driving force behind it was unclear. Neuroinflammation, fueled by activated microglia releasing pro-inflammatory cytokines and excitatory mediators, provides a plausible upstream mechanism.

This also helps explain why therapies that target microglial activation, such as low-dose naltrexone (LDN), show benefit in fibromyalgia. LDN is thought to modulate microglial activity, reducing the neuroinflammatory cascade that sustains central sensitization.

Small Fiber Neuropathy: A Peripheral Component

While fibromyalgia has traditionally been viewed as a purely central disorder, research over the past decade has revealed that many patients have objectively measurable peripheral nerve damage. Skin punch biopsy studies consistently find reduced intraepidermal nerve fiber density (IENFD) in 40-60% of fibromyalgia patients, meeting the diagnostic criteria for small fiber neuropathy (SFN) [13].

Small fiber nerves transmit pain and temperature signals and control autonomic functions. Their loss or damage could contribute to:

• Peripheral pain generation that feeds into and reinforces central sensitization
• Autonomic symptoms (temperature dysregulation, sweating abnormalities, GI motility issues)
• The burning, tingling, or “pins and needles” sensations that many fibromyalgia patients describe

This finding is clinically relevant because it suggests that fibromyalgia isn’t exclusively a brain problem. There’s a real, measurable peripheral nerve pathology in a significant subset of patients. Testing for SFN (skin punch biopsy or specialized nerve testing like QSART and sudomotor testing) may be worth pursuing, especially in patients with prominent neuropathic pain features.

The Gut-Brain Axis

The relationship between the gut microbiome and fibromyalgia has moved from speculation to documented science. A 2019 study published in Pain found that fibromyalgia patients had significantly altered gut microbiome composition compared to healthy controls. Specific bacterial species were correlated with pain severity, and the researchers could distinguish fibromyalgia patients from controls based on microbiome analysis alone with 87% accuracy [14].

The gut-brain connection in fibromyalgia likely operates through several pathways:

• Immune activation: Dysbiosis (microbial imbalance) increases intestinal permeability (“leaky gut”), allowing bacterial components like lipopolysaccharide (LPS) to enter the bloodstream and trigger systemic inflammation.
• Neurotransmitter production: Gut bacteria produce or influence the production of serotonin, GABA, and dopamine. Altered microbial composition directly affects the neurochemistry of pain modulation.
• Vagus nerve signaling: The gut communicates with the brain through the vagus nerve. Dysbiotic gut flora generate aberrant vagal signaling that can influence central pain processing.
• Short-chain fatty acid production: Beneficial bacteria produce butyrate and other short-chain fatty acids that have anti-inflammatory effects. Reduced production may contribute to both gut and systemic inflammation.

This research opens the door to microbiome-targeted therapies. While specific probiotic protocols for fibromyalgia haven’t been established in large trials, optimizing gut health through dietary fiber, fermented foods, and targeted probiotics is a reasonable and low-risk component of a comprehensive management strategy.

Autonomic Dysfunction

Autonomic nervous system dysfunction is present in the majority of fibromyalgia patients. Heart rate variability (HRV) studies consistently show reduced vagal tone and sympathetic predominance, meaning the “fight or flight” branch of the autonomic nervous system is chronically overactive while the “rest and digest” branch is underperforming [15].

This sympathetic overdrive contributes to:

• Sleep disruption (the nervous system is too activated to transition smoothly into deep sleep)
• Widespread muscle tension and pain (sustained sympathetic activation increases muscle tone)
• Fatigue (the body is burning energy maintaining a state of hypervigilance)
• Cognitive dysfunction (sympathetic dominance impairs prefrontal cortex function)
• GI symptoms (sympathetic activation slows gut motility)

Overlap with POTS (postural orthostatic tachycardia syndrome) is common. Some studies report that up to 70% of fibromyalgia patients have orthostatic intolerance on tilt-table testing. Whether autonomic dysfunction is a cause, consequence, or co-occurring feature of fibromyalgia is still debated, but addressing it (through vagal toning exercises, breathing techniques, and beta-blockers or other autonomic-modulating medications) often produces meaningful symptom improvement.

Risk Factors: Who Gets Fibromyalgia?

Based on the research, the highest-risk profile includes:

• Sex: Female (2-3x higher risk, though male fibromyalgia is underdiagnosed)
• Age: Peak onset between 30-50 years old, though it can develop at any age
• Family history: First-degree relative with fibromyalgia or another chronic pain condition
• History of trauma: Physical trauma (especially whiplash), childhood adverse experiences, PTSD
• Other pain conditions: Pre-existing conditions like IBS, TMJ disorder, endometriosis, or chronic headaches (central sensitization conditions tend to cluster)
• Sleep disorders: Chronic insomnia or untreated sleep apnea
• Autoimmune disease: Rheumatoid arthritis, lupus, and other autoimmune conditions frequently co-occur with fibromyalgia
• Obesity: Adipose tissue produces inflammatory cytokines, and mechanical loading increases peripheral pain input. Weight management may reduce fibromyalgia severity in some patients.

Why Understanding Causes Matters for Treatment

Knowing what’s driving your fibromyalgia changes how you treat it. If neuroinflammation is prominent, LDN or other microglial modulators make sense. If gut dysbiosis is a major contributor, microbiome restoration is a priority. If autonomic dysfunction is severe, vagal toning and autonomic-modulating strategies should be part of the plan. If a specific trauma triggered the onset, trauma-informed therapy (EMDR, somatic experiencing) may address a root cause that medications alone cannot.

Fibromyalgia is not one disease with one cause. It’s a final common pathway that different combinations of genetic, environmental, and physiological factors can converge upon. The most effective treatment plans account for this complexity and target the specific contributing factors present in each individual patient.

Related Reading

• Fibromyalgia: Understanding Central Sensitization and Your Treatment Options (Pillar)
• Fibromyalgia Treatment: Medications, Lifestyle Changes, and Emerging Therapies That Actually Help
• Chronic Fatigue Syndrome Treatment: What Helps and What Doesn’t
• Dysautonomia Symptoms: Recognizing Autonomic Nervous System Dysfunction
• Leaky Gut Symptoms: What the Science Actually Supports
• POTS Treatment: Managing Postural Orthostatic Tachycardia Syndrome

References

1. Woolf CJ. Central sensitization: implications for the diagnosis and treatment of pain. Pain. 2011;152(3 Suppl):S2-S15. doi:10.1016/j.pain.2010.09.030
2. Gracely RH, Petzke F, Wolf JM, Clauw DJ. Functional magnetic resonance imaging evidence of augmented pain processing in fibromyalgia. Arthritis Rheum. 2002;46(5):1333-1343. doi:10.1002/art.10225
3. Russell IJ, Vaeroy H, Javors M, Nyberg F. Cerebrospinal fluid biogenic amine metabolites in fibromyalgia/fibrositis syndrome and rheumatoid arthritis. Arthritis Rheum. 1992;35(5):550-556. doi:10.1002/art.1780350509
4. Arnold LM, Hudson JI, Hess EV, et al. Family study of fibromyalgia. Arthritis Rheum. 2004;50(3):944-952. doi:10.1002/art.20042
5. Gursoy S, Erdal E, Herken H, et al. Significance of catechol-O-methyltransferase gene polymorphism in fibromyalgia syndrome. Rheumatol Int. 2003;23(3):104-107. doi:10.1007/s00296-002-0257-5
6. Vargas-Alarcon G, Alvarez-Leon E, Fragoso JM, et al. A SCN9A gene-encoded dorsal root ganglia sodium channel polymorphism associated with severe fibromyalgia. BMC Musculoskelet Disord. 2012;13:23. doi:10.1186/1471-2474-13-23
7. Buskila D, Neumann L, Vaisberg G, Alkalay D, Wolfe F. Increased rates of fibromyalgia following cervical spine injury. A controlled study of 161 cases of traumatic injury. Arthritis Rheum. 1997;40(3):446-452. doi:10.1002/art.1780400310
8. Hickie I, Davenport T, Wakefield D, et al. Post-infective and chronic fatigue syndromes precipitated by viral and non-viral pathogens: prospective cohort study. BMJ. 2006;333(7568):575. doi:10.1136/bmj.38933.585764.AE
9. Ursini F, Ciaffi J, Mancarella L, et al. Fibromyalgia: a new facet of the post-COVID-19 syndrome spectrum? Results from a web-based survey. RMD Open. 2021;7(3):e001735. doi:10.1136/rmdopen-2021-001735
10. Hauser W, Kosseva M, Uceyler N, Klose P, Sommer C. Emotional, physical, and sexual abuse in fibromyalgia syndrome: a systematic review with meta-analysis. Arthritis Care Res. 2011;63(6):808-820. doi:10.1002/acr.20328
11. Craft RM. Modulation of pain by estrogens. Pain. 2007;132(Suppl 1):S3-S12. doi:10.1016/j.pain.2007.09.028
12. Albrecht DS, Forsberg A, Sandstrom A, et al. Brain glial activation in fibromyalgia: a multi-site positron emission tomography investigation. Brain Behav Immun. 2019;75:72-83. doi:10.1016/j.bbi.2018.09.018
13. Oaklander AL, Herzog ZD, Downs HM, Klein MM. Objective evidence that small-fiber polyneuropathy underlies some illnesses currently labeled as fibromyalgia. Pain. 2013;154(11):2310-2316. doi:10.1016/j.pain.2013.06.001
14. Minerbi A, Gonzalez E, Brereton NJ, et al. Altered microbiome composition in individuals with fibromyalgia. Pain. 2019;160(11):2589-2602. doi:10.1097/j.pain.0000000000001640
15. Martinez-Lavin M. Fibromyalgia as a sympathetically maintained pain syndrome. Curr Pain Headache Rep. 2004;8(5):385-389. doi:10.1007/s11916-996-0012-4