Fibromyalgia , diagnostic criteria and notes as per harrison

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Fibromyalgia - Diagnostic Criteria & Clinical Notes

Harrison's Principles of Internal Medicine, 22nd Edition (2025), Chapter 385

Definition

Fibromyalgia (FM) is characterized by chronic widespread musculoskeletal pain and tenderness. It is defined primarily as a pain syndrome, but patients also commonly report associated neuropsychological symptoms: fatigue, unrefreshing sleep, cognitive dysfunction, anxiety, and depression. Available evidence implicates the central nervous system as the key driver of pain and other core symptoms. FM is part of the broader group of chronic overlapping pain conditions (also including myalgic encephalitis/chronic fatigue syndrome, temporomandibular disorder, irritable bowel syndrome, interstitial cystitis, and other pelvic pain syndromes).

Epidemiology

Worldwide prevalence ~2%; ~4% in women, <1% in men
Female:male ratio in clinical settings ~8:1; in population studies ~3:1
Prevalence rises to 10-30% in patients with rheumatic diseases (RA, SLE), likely because these serve as peripheral pain generators
Over 5 million Americans affected
Additional risk factors: sleep disturbance, physical inactivity, overweight/obesity

2016 Diagnostic Criteria (Wolfe et al., revised from 2010/2011)

All three of the following must be met:

Criterion 1 - Widespread Pain Index (WPI) + Symptom Severity Score (SSS):

WPI ≥ 7 AND SSS ≥ 5 OR WPI 4-6 AND SSS ≥ 9

Criterion 2 - Generalized pain in at least 4 of 5 regions (jaw/neck/chest/abdomen count as axial)

Criterion 3 - Symptoms present at a similar level for at least 3 months

WPI body map - Widespread Pain Index scoring regions

FIGURE 385-1, Harrison's 22E - FM 2016 Diagnostic Criteria

Widespread Pain Index (WPI) - Scoring (max 19)

The patient indicates where they had pain during the past week from the following 19 regions:

Side	Regions
Right	Jaw, Shoulder, Upper Arm, Lower Arm, Hip/Buttocks, Upper Leg, Lower Leg
Left	Jaw, Shoulder, Upper Arm, Lower Arm, Hip/Buttocks, Upper Leg, Lower Leg
Axial	Neck, Chest/Breast, Abdomen, Upper Back, Lower Back

Symptom Severity Score (SSS) - Scoring (max 12)

Part A - Over the past week (0 = no problem, 1 = slight/mild, 2 = moderate, 3 = severe):

Fatigue (0-3)
Trouble thinking or remembering (0-3)
Waking up tired/unrefreshed (0-3)

Part B - During the past 6 months (Yes = 1, No = 0):

Pain or cramps in the abdomen
Depression
Headache

SSS total = Part A (0-9) + Part B (0-3) = 0-12

Clinical Manifestations

Pain and Tenderness

Patients report "pain all over" - poorly localized, severe, with reduced function
Widespread pain = both above and below the waist, both sides of the body, involving the axial skeleton (neck, back, or chest)
Pain present most of the day on most days for ≥ 3 months (required for diagnosis)
Associated tenderness and elevated evoked pain sensitivity (hyperalgesia, allodynia)
The older 1990 ACR criteria required ≥ 11 of 18 tender points at ~4 kg/m² pressure (thumbnail blanching pressure) - this is no longer required by current criteria

Neuropsychological Symptoms

Fatigue (often profound)
Unrefreshing sleep
Cognitive dysfunction ("fibro fog")
Anxiety and depression

Overlapping Syndromes

Headaches, facial/jaw pain, regional myofascial pain
Visceral pain: GI, bladder, pelvic/perineal
Importantly, FM often coexists with other overlapping conditions and treatment of one may help global symptom management

Differential Diagnosis (Table 385-1)

Category	Conditions
Inflammatory	Polymyalgia rheumatica, RA, spondyloarthritides, SLE, Sjögren's syndrome
Infectious	Hepatitis C, HIV, Lyme disease, Parvovirus B19, EBV
Noninflammatory	Degenerative joint/spine/disk disease, myofascial pain syndrome, bursitis, tendinitis
Endocrine	Hypothyroidism, hyperthyroidism, hyperparathyroidism
Neurologic	Multiple sclerosis, neuropathic pain syndromes
Psychiatric	Major depressive disorder
Drugs	Statins, aromatase inhibitors

Laboratory & Radiographic Testing (Table 385-2)

Routine (all FM patients):

ESR or CRP
CBC
TSH

Guided by History and Physical Exam:

Complete metabolic panel
ANA
Anti-SSA and anti-SSB
RF and anti-CCP
Creatine phosphokinase (CPK)
Viral/bacterial serologies (Hep C, HIV, Lyme)
Spine and joint radiographs (only if inflammatory arthritis features present)

Key note: Routine labs and imaging are normal in uncomplicated FM. MRI of the spine should be discouraged unless there are features of inflammatory spine disease or neurologic symptoms. Repeat testing after initial evaluation is also discouraged.

Pathogenesis

Genetic predisposition: polymorphisms in pathways controlling serotonin and monoamine metabolism/transport, and other pain transmission pathways
Psychophysical testing shows altered sensory afferent pain processing and impaired descending noxious inhibitory control → hyperalgesia and allodynia
Functional MRI demonstrates brain activation in pain-processing regions in response to innocuous stimuli
Pain perception modulated by emotional/cognitive factors (catastrophizing, perceptions of control) - basis for CBT recommendations
Some patients may have small fiber neuropathy; early reports suggest possible autoimmune etiology in a subset
Potential future: confirmatory diagnostic testing from gene expression or metabolic signatures in peripheral blood

Treatment

Nonpharmacologic (first-line, most effective)

Physical conditioning/aerobic exercise - consistently the most helpful intervention; start low, advance slowly
Supervised or water-based programs for deconditioned patients
Strength training after aerobic goals achieved
FDA-approved devices: laser therapy device; TENS (large RCT showed reduction in movement-evoked pain and fatigue)
Meditative movement: qigong, yoga, Tai Chi
Acupuncture, hydrotherapy
Cognitive-behavioral therapy (CBT) for sleep hygiene and illness behaviors
Patient education about genetics, triggers, and physiology of FM

Pharmacologic (Table 385-3)

Drug	Dose
Cyclobenzaprine (muscle relaxant)	10-40 mg/day, at bedtime or divided up to 4x/day
Amitriptyline (TCA, SNRI activity)	10-50 mg/day at bedtime
Duloxetine (SNRI) - FDA approved	60 mg/day; start at 30 mg/day for 1 week
Milnacipran (SNRI) - FDA approved	50 mg BID; titrate over 7 days
Pregabalin (α2-δ ligand) - FDA approved	150-450 mg/day; start 75 mg BID ≥ 1 week
Tramadol	37.5 mg + 325 mg acetaminophen up to 4x/day

Key prescribing notes:

NSAIDs and glucocorticoids may treat inflammatory triggers but are not effective for FM symptoms
Strong opioids are to be avoided - no demonstrated efficacy and worsen symptoms/function
Tramadol: generally discouraged due to opioid-related adverse effects despite some evidence
Choose agents that address multiple symptom domains simultaneously:
- Pain + sleep disturbance → cyclobenzaprine, amitriptyline, gabapentin, pregabalin
- Pain + fatigue/anxiety/depression → duloxetine or milnacipran

Approach to the Patient

Optimal management requires prompt diagnosis + assessment of pain, function, and psychosocial context
Developing a patient-clinician partnership is essential
Focus on improved function and quality of life, not elimination of pain
Discourage illness behaviors (frequent physician visits); encourage function-focused behaviors
Identify and treat comorbid triggering conditions separately

Source: Harrison's Principles of Internal Medicine, 22nd Edition (2025), Chapter 385 (Fibromyalgia) and Chapter 382 (Approach to the Patient with Musculoskeletal Disease).

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