Fibromyalgia UK: Symptoms, Diagnosis & What Causes It

A clinically reviewed UK conditions guide to fibromyalgia — central sensitisation, widespread pain, fatigue, diagnosis criteria, evidence-based management, and when to seek specialist assessment.

What Is Fibromyalgia?

Fibromyalgia is classified by the International Association for the Study of Pain as a nociplastic pain condition — pain arising from altered pain processing in the nervous system without identifiable tissue damage or nerve pathology. It is not an inflammatory arthritis, not a degenerative joint disease, and not a psychiatric condition — though it has significant overlap with anxiety and depression and is aggravated by psychological stress.

The key concept is central sensitisation: the central nervous system (brain and spinal cord) becomes amplified in its pain responses, interpreting normal or mild stimuli as painful, and magnifying painful stimuli beyond what the peripheral input would suggest. The pain in fibromyalgia is real — it is generated by a nervous system that has become persistently overresponsive.

How Common Is Fibromyalgia?

Fibromyalgia affects an estimated 1–2% of the UK population — approximately 800,000 to 1.2 million people. It is one of the most common conditions seen in rheumatology clinics. It most commonly presents in adults aged 30–60, though it can occur at any age. Women are diagnosed approximately 7 times more often than men in clinical populations, though this ratio may partly reflect under-recognition in men.

What Causes Fibromyalgia?

The precise cause remains incompletely understood. Current evidence points to a combination of:

• Genetic predisposition — fibromyalgia runs in families; variants in genes involved in serotonin, dopamine, and catecholamine metabolism are associated with increased risk
• Central sensitisation — altered neurological pain processing; reduced inhibitory pain control (descending modulation); altered pain neurotransmitter levels — some studies have found elevated substance P and reduced serotonin in cerebrospinal fluid, though findings vary across research
• Triggers — fibromyalgia often begins or worsens following a trigger: physical injury or illness, significant psychological stress, infection (post-viral fibromyalgia has been increasingly recognised following COVID-19), or surgery
• Sleep disturbance — disrupted deep sleep (stage 3 NREM) itself lowers pain thresholds, creating a reinforcing cycle
• Autonomic nervous system dysregulation — abnormal sympathetic nervous system activity; links to fatigue, cardiovascular symptoms, and functional bowel disturbance

Symptoms

• Widespread pain — the core symptom; present in multiple body areas; aching, burning, or stabbing; often migratory; characteristically worse after physical activity, cold, stress, or poor sleep
• Fatigue — often described as profound and unrestorative; not simply tiredness; persistent even after adequate sleep; significantly affects function
• Sleep disturbance — non-restorative sleep; difficulty falling or staying asleep; waking unrefreshed despite adequate hours; disrupted deep sleep (NREM stage 3) is both a symptom and a contributor
• Cognitive difficulties — often called “fibro fog”; word-finding difficulty, poor concentration, memory lapses; can be as disabling as the pain
• Heightened sensory sensitivity — allodynia (pain from light touch); hyperalgesia (exaggerated pain response); sensitivity to loud noise, bright light, odours, and temperature
• Headaches — tension-type or migraine headaches are common in fibromyalgia
• Bowel and bladder symptoms — irritable bowel syndrome coexists in up to 50%; urgency and frequency of urination
• Mood symptoms — anxiety and depression coexist in the majority; may precede or follow fibromyalgia onset

Central Sensitisation: The Mechanism

Central sensitisation explains why fibromyalgia produces widespread pain in the absence of identifiable tissue damage. In the normal pain system, peripheral nociceptors signal injury or inflammation, the spinal cord relays the signal, and the brain constructs the pain experience. Descending pathways from the brain then provide inhibitory control — damping signals when they are not useful.

In fibromyalgia, this inhibitory control is significantly impaired. The brain’s pain-processing regions are persistently in a heightened state — responding to inputs that would normally be filtered out, amplifying incoming signals, and failing to apply normal inhibition. Neuroimaging studies show abnormal activation patterns in pain-processing brain regions in fibromyalgia patients at rest and in response to non-painful stimuli.

This is why treatments targeting peripheral inflammation (NSAIDs, corticosteroids) have limited effectiveness in fibromyalgia — the problem is not peripheral. Treatments that target central pain processing (low-dose tricyclics, SNRIs, aerobic exercise, cognitive behavioural therapy) address the actual mechanism.

Diagnosis

There is no diagnostic blood test or imaging finding for fibromyalgia. Diagnosis is clinical, based on the 2016 revised diagnostic criteria from the American College of Rheumatology:

• Widespread pain index (WPI) — count of body areas painful in the past week; ≥7 of 19 areas (or 4–6 with symptom severity score ≥9)
• Symptom severity score (SSS) — rating of fatigue, non-restorative sleep, and cognitive symptoms; total SSS ≥5
• Duration — symptoms present at similar levels for at least 3 months
• No other diagnosis explains the symptoms — investigations are used to exclude alternative diagnoses, not to confirm fibromyalgia

Investigations at diagnosis typically include FBC, ESR/CRP, thyroid function, and rheumatoid factor — to exclude inflammatory arthritis, hypothyroidism, and other conditions that can present with similar symptoms. Normal results support fibromyalgia; they do not mean the symptoms are not real.

Coexisting Conditions

Fibromyalgia rarely occurs in isolation. Common coexisting conditions include:

• Irritable bowel syndrome (IBS) — up to 50–70% of patients
• Anxiety and depression — majority of patients; bidirectional relationship
• Migraine or chronic daily headache — 30–50%
• Chronic fatigue syndrome (ME/CFS) — significant symptom overlap; some consider them on the same spectrum
• Temporomandibular joint (TMJ) disorders
• Interstitial cystitis

Treatment Overview

Management of fibromyalgia is multimodal. No single treatment is sufficient. The most effective approach combines physical, psychological, and pharmacological elements — with non-pharmacological approaches as the foundation.

When to Seek Help

• Widespread pain lasting more than 3 months that is significantly affecting your daily life
• Symptoms consistent with fibromyalgia that have not been properly evaluated
• Current management is not adequately controlling your symptoms
• You are experiencing significant mood symptoms alongside pain and fatigue