Fibromyalgia vs Polymyositis and Dermatomyositis
Fibromyalgia and Polymyositis and Dermatomyositis are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.
Fibromyalgia vs Polymyositis and Dermatomyositis at a glance
- Fibromyalgia: Centralized pain syndrome with widespread tenderness, fatigue, and sleep and cognitive disturbance; normal labs and imaging.
- Polymyositis and Dermatomyositis: Idiopathic inflammatory myopathies causing symmetric proximal muscle weakness; dermatomyositis adds skin findings.
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Side-by-side comparison
| Feature | Fibromyalgia | Polymyositis and Dermatomyositis |
|---|---|---|
| At a glance | Centralized pain syndrome with widespread tenderness, fatigue, and sleep and cognitive disturbance; normal labs and imaging. | Idiopathic inflammatory myopathies causing symmetric proximal muscle weakness; dermatomyositis adds skin findings. |
| Classic presentation | Diffuse musculoskeletal pain >3 months in multiple body regions, often migratory; Profound fatigue, especially morning fatigue and after exertion; Nonrestorative sleep, frequent awakenings; Cognitive symptoms — word-finding difficulty, decreased concentration ('fibro fog'); Headache, paresthesias, dizziness; GI symptoms (IBS overlap),… | Middle-aged woman with several months of progressive symmetric proximal weakness, a violaceous (heliotrope) rash over the upper eyelids, and Gottron papules over the knuckles.; Symmetric proximal muscle weakness — difficulty rising from a chair, climbing stairs, lifting arms overhead, combing hair; Insidious onset over weeks to months;… |
| Workup / key labs | 2016 ACR criteria: widespread pain index (WPI) and symptom severity scale (SSS) — pain in 4 of 5 body regions for ≥3 months with WPI ≥7 and SSS ≥5 (or WPI 4-6 and SSS ≥9), and no alternative diagnosis.; Goal is to exclude alternative explanations — not to confirm fibromyalgia; CBC, CMP, TSH, CRP, ESR, CK, vitamin D, vitamin B12;… | Bohan and Peter criteria (historic) and EULAR/ACR 2017 criteria. Classic features include symmetric proximal weakness, elevated muscle enzymes, characteristic EMG findings (small polyphasic motor unit potentials, fibrillations, positive sharp waves), and muscle biopsy demonstrating perivascular inflammation (DM) or endomysial CD8+… |
| Imaging | Generally NOT indicated — incidental findings on MRI commonly mislead; Image only if focal red-flag findings emerge (true weakness, focal joint signs, neurologic deficits) | MRI of affected muscles — T2 hyperintensity reflecting edema; guides biopsy site; High-resolution chest CT for interstitial lung disease, particularly if anti-Jo-1 or anti-MDA5 positive; Pulmonary function testing including DLCO; Echocardiogram if cardiac involvement suspected |
| First-line treatment | Patient education — emphasize that pain is real, reflects altered central pain processing, and is not destructive or progressive; Aerobic exercise — graded, low-impact (walking, swimming, cycling); cornerstone of treatment; Sleep hygiene and treatment of sleep disorders (OSA, restless legs); Cognitive behavioral therapy and… | High-dose corticosteroids — prednisone 1 mg/kg/day (up to 60-80 mg) until objective improvement, then taper over 9-12 months; Methylprednisolone pulses for severe weakness, dysphagia, or rapidly progressive interstitial lung disease; Steroid-sparing agent introduced early to limit cumulative steroid exposure: methotrexate or… |
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