Fibromyalgia & Common Soft-Tissue Disorders
A Step 2 CK-focused lesson on fibromyalgia (central sensitization, normal labs, exercise + duloxetine/amitriptyline first-line, avoid opioids) and common soft-tissue disorders, using classic vignette buzzwords, next-best-step logic, and comparison tables for the chronic-widespread-pain differential and synovial fluid analysis.
Pathophysiology & Overview
Fibromyalgia is a disorder of central pain amplification (central sensitization) — not peripheral inflammation or tissue damage. The CNS misprocesses pain: hyperalgesia (amplified pain) and allodynia (pain from non-painful stimuli), elevated CSF substance P and glutamate, and reduced descending serotonin/norepinephrine inhibition.
The hallmark is chronic widespread pain ≥3 months plus fatigue, non-restorative sleep, and cognitive difficulty ("fibro fog"). Because there is no inflammation, ESR, CRP, CK, and autoantibodies are normal — labs are ordered to exclude mimics, not to confirm the diagnosis.
It predominantly affects women 20–55 and clusters with IBS, tension/migraine headache, interstitial cystitis, temporomandibular disorder, depression, and anxiety. Boards frame it as a positive clinical diagnosis: once mimics are reasonably excluded, resist the trap of ordering ever more tests and imaging.
- Diagnosis (2016 ACR): widespread pain (Widespread Pain Index) + symptom-severity score (fatigue, sleep, cognition) for ≥3 months. The old 1990 criteria requiring 11/18 tender points are no longer required.
- Labs to exclude mimics: CBC, TSH, ESR/CRP, CK, vitamin D. Order ANA/RF only if autoimmune features are present — reflex ANA creates false-positive traps.
- First-line = graded aerobic exercise + patient education (strongest evidence); add CBT and sleep hygiene.
- Drugs: duloxetine or milnacipran (SNRI), amitriptyline (TCA), pregabalin/gabapentin. Duloxetine, milnacipran, and pregabalin are FDA-approved for fibromyalgia.
- Avoid opioids (ineffective, harmful) and glucocorticoids; NSAIDs are largely ineffective as monotherapy because there is no inflammation.
Vignette: A 38-year-old woman reports 8 months of diffuse body pain, profound fatigue, un-refreshing sleep, and poor concentration. Exam shows tenderness at many sites but no synovitis, joint swelling, weakness, or rash. CBC, TSH, ESR, CRP, and CK are all normal.
- Diagnosis: Fibromyalgia.
- Next best step: Reassurance/education + start a graded aerobic exercise program. Do NOT order more autoantibody panels or MRIs.
- If pharmacotherapy is needed for pain/sleep: duloxetine or low-dose amitriptyline.
- Buzzwords: "pain everywhere," normal inflammatory markers, non-restorative sleep, fibro fog, tender but not swollen.
Contrast trap: new proximal girdle stiffness with a high ESR in a patient >50 points to polymyalgia rheumatica, not fibromyalgia.
Differential of Chronic Widespread Pain
| Condition | Key features | ESR/CRP | Autoantibodies | Distinguishing clue |
|---|---|---|---|---|
| Fibromyalgia | Widespread pain, fatigue, fibro fog; no synovitis | Normal | None | Normal labs; central sensitization |
| PMR | Age >50; shoulder/hip-girdle stiffness | High (often >40) | Neg (RF/CCP−) | Dramatic response to low-dose prednisone; assoc. GCA |
| RA | Symmetric small-joint synovitis, AM stiffness >1h | High | RF, anti-CCP | Erosions on X-ray; inflammatory joint fluid |
| SLE | Arthralgia, rash, cytopenias, nephritis | ESR ↑; CRP often normal | ANA (screen); anti-dsDNA/Smith (specific) | Multisystem; non-erosive (Jaccoud) arthritis; ↑CRP suggests infection/serositis |
| Hypothyroidism | Fatigue, myalgia, cold intolerance | Normal | Anti-TPO (if Hashimoto) | ↑TSH; may have ↑CK |
- Rotator cuff tendinopathy/impingement: supraspinatus most common; painful arc, +empty-can (Jobe). A positive drop-arm test suggests a full-thickness tear.
- Adhesive capsulitis (frozen shoulder): loss of both active AND passive ROM (esp. external rotation); associated with diabetes.
- Lateral epicondylitis (tennis elbow): pain on resisted wrist extension. Medial (golfer's elbow): resisted wrist flexion/pronation.
- De Quervain tenosynovitis: radial-sided wrist pain (APL/EPB); +Finkelstein test; new mothers, repetitive thumb use.
- Trochanteric bursitis (greater trochanteric pain syndrome): lateral hip pain, worse lying on that side; point tenderness over the greater trochanter.
- Plantar fasciitis: heel pain worst with first morning steps; tender at the medial calcaneal tuberosity.
- Management pattern: relative rest, NSAIDs, PT/stretching → corticosteroid injection; avoid injecting into tendons.
Vignette: A 32-year-old pregnant woman (or data-entry clerk) has 6 weeks of nocturnal numbness/tingling in the thumb, index, middle, and radial half of the ring finger, relieved by shaking the hand (flick sign). Tinel and Phalen reproduce symptoms; no thenar atrophy.
- Diagnosis: Carpal tunnel syndrome (median neuropathy at the wrist).
- Next best step: Nocturnal neutral-position wrist splint (first-line for mild–moderate). Confirm with nerve conduction studies/EMG if diagnosis is uncertain.
- Escalate: corticosteroid injection → surgical carpal tunnel release if thenar atrophy or refractory/severe disease.
- Associations: pregnancy, hypothyroidism, diabetes, RA, acromegaly, repetitive wrist use.
"LOAF" = the intrinsic hand muscles supplied by the median nerve and weakened in advanced carpal tunnel syndrome:
- L — Lateral two Lumbricals (index, middle)
- O — Opponens pollicis
- A — Abductor pollicis brevis
- F — Flexor pollicis brevis (superficial head)
Thenar wasting + weak thumb abduction/opposition = advanced CTS → consider surgical release.
Classic pearl: sensation over the thenar eminence (palmar base) is spared, because the palmar cutaneous branch of the median nerve arises proximal to the carpal tunnel and travels superficial to it — so it is not compressed.
Synovial Fluid Analysis
| Category | WBC (/µL) | Appearance | Examples / crystals |
|---|---|---|---|
| Normal | <200 | Clear, transparent | Healthy joint |
| Non-inflammatory | 200–2,000 | Clear/straw | OA, trauma |
| Inflammatory | 2,000–50,000 | Cloudy, yellow | RA; gout (needle, negative birefringence); pseudogout/CPPD (rhomboid, positive birefringence); spondyloarthritis |
| Septic | >50,000 (often >100k), >90% PMNs | Purulent, opaque | Bacterial (S. aureus, gonococcus) |
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