Fibromyalgia and Chronic Pain

Mechanistic groupings

• Genetic/neurotransmitter: Familial aggregation is strong — first-degree relatives of probands have substantially increased risk. Polymorphisms affecting catecholamine breakdown (COMT) and serotonin transport bias descending inhibitory pathways toward under-function.
• Peripheral/traumatic trigger: Motor vehicle collision, surgery, or regional injury can initiate persistent nociceptive input that drives central sensitization ("windup") long after tissue healing.
• Post-infectious: Symptoms may follow viral illness (including EBV and post-acute COVID-19 syndromes) or treated Lyme disease — the classic stem is persistent diffuse pain and fatigue after a completed, adequate antibiotic course, often with persistently positive IgG serology, which reflects prior exposure and is not an indication for repeat antibiotics (IDSA/AAN/ACR Lyme disease guidance advises against prolonged or repeat antibiotic courses).
• Psychosocial/neuroendocrine: Childhood adversity or abuse, PTSD, and combat deployment blunt HPA-axis reactivity and are consistently over-represented.
• Comorbid rheumatologic disease: RA, SLE, axial spondyloarthritis, and Sjögren syndrome each carry high rates of secondary fibromyalgia from sustained nociceptive drive.

Non-modifiable risk factors

• Female sex: 75–90% of cases, the single most tested demographic anchor.
• Middle age: Peak incidence in the fourth to sixth decades, though pediatric and elderly cases occur.
• Family history / genotype: Heritability is substantial; fibromyalgia is now classified as a nociplastic pain disorder (IASP terminology) with familial clustering. Note that the widely used 2016 criteria are a published revision of the ACR 2010/2011 criteria rather than a formally ACR-endorsed guideline.
• Pre-existing autoimmune or chronic pain disease.

Modifiable risk factors

• Poor sleep and untreated obstructive sleep apnea: Loss of slow-wave sleep is both cause and consequence; screen and treat independently.
• Physical deconditioning: Inactivity lowers pain thresholds; EULAR's 2016 fibromyalgia recommendations reserve their strongest endorsement for exercise.
• Obesity: Associated with greater symptom severity and worse response to therapy.
• Depression, anxiety, and pain catastrophizing: Targets of CBT.
• Chronic opioid exposure: Promotes opioid-induced hyperalgesia and worsens the underlying sensitization.
• Smoking and low health literacy/socioeconomic strain.

• Dysregulation of pain neurotransmitters: Decreased norepinephrine, serotonin, and dopamine in the central nervous system lead to altered pain modulation; increased levels of substance P (an excitatory pain neurotransmitter) in cerebrospinal fluid amplify pain signaling
• Central sensitization: Progressive amplification of pain processing at the spinal cord and brain level results in allodynia (pain from normally non-painful stimuli) and hyperalgesia (exaggerated pain response); this involves increased activity of excitatory glutamate and NMDA receptors
• Neuroendocrine dysfunction: Abnormal hypothalamic-pituitary-adrenal (HPA) axis function with reduced cortisol response to stress; altered growth hormone secretion during sleep contributes to non-restorative sleep
• Neuroinflammation: Glial cell activation (particularly microglia) produces pro-inflammatory cytokines (IL-6, TNF-α) that enhance pain transmission
• Sleep architecture abnormalities: Defective slow-wave sleep leads to impaired tissue repair, accumulation of metabolic waste, and perpetuation of pain; increased alpha-wave intrusion during non-REM sleep causes fragmentation
• Genetic predisposition: Polymorphisms in genes encoding serotonin receptors, catecholamine-metabolizing enzymes (COMT), and serotonin transporters increase susceptibility
• Environmental triggers: Physical or emotional trauma, infections (including viral pathogens), and major life stressors can unmask or exacerbate fibromyalgia in genetically predisposed individuals

• Widespread pain: Bilateral, symmetrical pain affecting axial skeleton (neck, lower back) and extremities; patients often describe diffuse, poorly localized pain without swelling or visible inflammation; pain fluctuates in intensity and can be exacerbated by stress, cold weather, and physical overexertion
• Fatigue: Profound exhaustion that is out of proportion to activity level; non-restorative ("waking unrefreshed") despite adequate sleep duration; described as "brain fog" or cognitive dysfunction with difficulty concentrating, memory problems, and slow processing speed (often called fibrofog)
• Sleep disturbance: Insomnia, frequent awakening, early morning awakening, and non-restorative sleep are nearly universal; patients may report vivid nightmares or restless sleep
• Somatic symptoms: Widespread tenderness on palpation (especially at tender points, though this is no longer diagnostic), morning stiffness (typically <1 hour, distinguishing from rheumatoid arthritis), paresthesias (numbness/tingling, often without objective sensory changes), and headaches (including migraine)
• Autonomic and mood symptoms: Temperature dysregulation (feeling too hot or cold), anxiety, depression (present in 40-60% of patients), irritable bowel syndrome (50-90%), and restless leg syndrome
• Important clinical pearl: Despite prominent pain complaints, objective physical examination findings are minimal or absent; there is no joint swelling, warmth, or erythema, and laboratory values are normal—this distinction is critical for diagnosis

• American College of Rheumatology (ACR) 2016 Diagnostic Criteria: (1) Widespread Pain Index (WPI) ≥7 and Symptom Severity (SS) scale score ≥5, OR WPI 4-6 and SS scale score ≥9; (2) symptoms present for ≥3 months; (3) absence of another medical condition that would otherwise explain the pain; this replaces older 1990 criteria that relied on "tender point" counts which were found to be unreliable
• Exclusionary testing (to rule out mimics): Normal ESR and CRP (to exclude inflammatory arthritides), normal TSH (to exclude hypothyroidism), normal CBC (to exclude anemia or hematologic malignancy), normal metabolic panel, and negative rheumatologic serologies (ANA, RF, anti-CCP) in appropriate clinical contexts; imaging is usually normal
• Brain imaging (PET, fMRI): Research tools showing increased central pain processing and reduced gray matter volume, but not used clinically for diagnosis
• Important diagnostic considerations:
• Fibromyalgia frequently coexists with other conditions (rheumatoid arthritis, lupus, osteoarthritis), so normal inflammatory markers do not exclude underlying rheumatologic disease
• Beware of diagnostic anchoring bias: patients with fibromyalgia may have an undiagnosed autoimmune disease; conversely, patients with autoimmune disease may have superimposed fibromyalgia
• Sleep disorders (obstructive sleep apnea, restless leg syndrome) and mood disorders should be screened and treated independently

• Pharmacologic first-line agents:
• Gabapentin: Starting dose 300 mg daily at bedtime, titrate to 900-3,600 mg/day in divided doses; mechanism involves reduction of substance P and calcium channel modulation; evidence-based for pain and sleep improvement
• Pregabalin: Starting dose 150 mg/day divided, titrate to 300-600 mg/day; similar mechanism to gabapentin with possibly faster onset; FDA-approved for fibromyalgia
• Duloxetine: Starting dose 30-60 mg daily, titrate to 60 mg daily; SNRI (serotonin-norepinephrine reuptake inhibitor) that increases descending inhibitory pain pathways; FDA-approved and particularly helpful if depression is present
• Tricyclic antidepressants (amitriptyline, cyclobenzaprine): Low-dose amitriptyline (10-50 mg at bedtime) improves sleep and pain; cyclobenzaprine 5-10 mg at bedtime acts as both muscle relaxant and sedating agent; older agents but remain effective

• Second-line pharmacologic options:
• Milnacipran (SNRI): Alternative to duloxetine; useful in patients who don't tolerate SSRIs
• NSAIDs: Generally ineffective as monotherapy but may provide adjunctive benefit; caution with long-term use due to GI and cardiovascular risks
• Low-dose naltrexone (LDN): Emerging evidence for 4.5 mg nightly; proposed mechanism involves microglial suppression and may benefit patients intolerant to other agents
• Avoid opioids: Ineffective for fibromyalgia, carry high addiction risk, may worsen central sensitization, and complicate management; use is generally contraindicated

• Non-pharmacologic interventions (often equal or superior to medications and should be emphasized):
• Aerobic exercise and strength training: Gold standard recommendation; low-impact activities (walking, swimming, water aerobics) 30-60 minutes 3-5x weekly; benefits include reduced pain, improved fatigue, and mood enhancement
• Cognitive behavioral therapy (CBT): Effective for pain management, mood disorders, and functional impairment; helps address maladaptive thought patterns and behavioral patterns perpetuating pain
• Sleep optimization: Sleep hygiene measures, treatment of comorbid sleep disorders, and consistent sleep schedule
• Mindfulness-based stress reduction (MBSR): Improves pain and quality of life through meditation and stress reduction
• Patient education: Critical component;

Complications of the disease

• Functional disability and work loss: Driven by fatigue and fibrofog more than by pain intensity; signaled by declining activity, disability claims, and social withdrawal.
• Major depressive disorder and suicidality: Shared serotonergic/noradrenergic deficits plus chronic pain burden; suicidal ideation in a fibromyalgia patient is an emergency requiring immediate risk assessment and safety planning per APA/DSM-5-TR–based practice.
• Iatrogenic harm from over-testing: A low-prevalence ANA ordered without clinical suspicion yields false positives, triggering cascades of imaging, biopsy, and unwarranted immunosuppression.
• Opioid-induced hyperalgesia and opioid use disorder: Chronic mu-agonist exposure upregulates pronociceptive signaling, so pain worsens as doses rise; the CDC 2022 opioid prescribing guideline favors nonopioid therapy for chronic musculoskeletal pain. Overdose with respiratory depression is an emergency (naloxone).
• Missed comorbid disease: Anchoring on fibromyalgia can mask new inflammatory arthritis, myositis, or malignancy — objective synovitis, weight loss, fever, or a rising ESR/CRP should never be attributed to fibromyalgia.

Complications of treatment

• Serotonin syndrome: Duloxetine or milnacipran combined with triptans, tramadol, linezolid, or MAOIs; look for clonus, hyperreflexia, agitation, hyperthermia, and diaphoresis. Emergency — stop serotonergic agents, cool, benzodiazepines, cyproheptadine if refractory.
• SNRI adverse effects: Hypertension, hepatotoxicity, hyponatremia from SIADH (confusion, seizure), and a flu-like discontinuation syndrome with abrupt stopping.
• Gabapentinoid toxicity: Sedation, dizziness, peripheral edema, and weight gain; the FDA warns of serious respiratory depression when pregabalin or gabapentin is combined with opioids or in COPD. Pregabalin is a Schedule V controlled substance with misuse potential; dose reduction is required in renal impairment.
• Tricyclic effects: Anticholinergic delirium, urinary retention, orthostasis, and QT prolongation; in overdose, QRS widening >100 ms signals sodium-channel blockade — an emergency treated with IV sodium bicarbonate.
• Cyclobenzaprine: Structurally a TCA, so it adds anticholinergic and serotonergic burden.
• NSAIDs/glucocorticoids: GI bleeding and cardiovascular risk without meaningful benefit; steroids have no role.

• The stem template: Middle-aged woman, ≥3 months of generalized pain involving at least 4 of 5 body regions (WPI-defined), wakes unrefreshed, "fibrofog," completely normal exam and normal ESR/CRP. Normal inflammatory markers with diffuse tenderness is the discriminating combination.
• Best next step is restraint, not testing: Confirm the 2016 criteria (a published revision of the ACR 2010/2011 criteria) clinically and order a limited screen — CBC, CMP, TSH, ESR/CRP. Do not reflexively order ANA, RF, anti-CCP, or MRI; in low pretest probability these generate false positives and diagnostic cascades.
• The buzzwords examiners plant: Allodynia, hyperalgesia, elevated CSF substance P, alpha-wave intrusion into non-REM (slow-wave) sleep, low CNS serotonin/norepinephrine. Tender points are 1990-criteria history — they are no longer diagnostic.
• The association most often tested: The functional-somatic cluster — irritable bowel syndrome, migraine, temporomandibular disorder, interstitial cystitis/painful bladder, restless legs, and depression/anxiety. Recognizing this cluster is often the answer itself.
• FDA-approved agents are three: pregabalin, duloxetine, and milnacipran. Amitriptyline, cyclobenzaprine, and gabapentin are used and effective but are off-label — a favorite fine-distinction question.
• Exercise outranks pills: EULAR's 2016 fibromyalgia recommendations give their strongest endorsement to graded aerobic exercise; CBT, sleep optimization, and patient education complete the core. If a vignette asks for the single best initial management, non-pharmacologic therapy is usually correct.
• Distractors to reject: Polymyalgia rheumatica (age >50, shoulder/hip girdle stiffness, markedly elevated ESR, dramatic steroid response), hypothyroidism (check TSH), RA (morning stiffness >1 hour with synovitis and erosions), polymyositis (weakness with high CK — fibromyalgia causes pain, not true weakness), and SLE.
• Two therapeutic traps: Glucocorticoids and opioids. Steroids do nothing in a non-inflammatory disorder, and opioids worsen central sensitization — consistent with the CDC 2022 guideline's preference for nonopioid therapy.