Confusable diagnoses · PANCE / PANRE

Fibromyalgia vs Polymyositis and Dermatomyositis

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

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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Question 1MusculoskeletalMedium
A 45-year-old woman presents with 6 months of widespread musculoskeletal pain that is bilateral and both above and below the waist, along with marked fatigue, non-restorative sleep, and difficulty concentrating. Examination reveals diffuse soft-tissue tenderness without synovitis, and 16 of 18 tender points are positive. CBC, comprehensive metabolic panel, TSH, ANA, and ESR are all within normal limits. Which intervention is the most appropriate initial therapy?
  • AAerobic exercise
  • BOral duloxetine
  • CTender point injections
  • DTizanidine at bedtime
Reveal answer & full explanation
Correct answer: A — Aerobic exercise
  • AAerobic exercise✓
  • BOral duloxetine
  • CTender point injections
  • DTizanidine at bedtime

Why Aerobic exercise is correct

  • This patient meets criteria for fibromyalgia: chronic (>3 months) widespread pain in all quadrants with fatigue, non-restorative sleep, cognitive symptoms (fibro fog), and 16 of 18 tender points positive
  • Normal inflammatory and metabolic workup (CBC, CMP, TSH, ANA, ESR) excludes inflammatory and endocrine mimics
  • The cornerstone of initial management is non-pharmacologic and patient-centered: education, graded aerobic exercise (strongest and most consistent evidence for improving pain, function, and global well-being), and cognitive behavioral therapy to address sleep, mood, and pain coping
  • EULAR and U.S. guidelines recommend these as first-line before drug therapy

Why the others are wrong

  • Oral duloxetine — an SNRI that is FDA-approved for fibromyalgia and a reasonable add-on if symptoms persist despite non-pharmacologic measures, but it is not the initial step; pregabalin and milnacipran fill the same second-line role
  • Tender point injections — local anesthetic injection targets focal myofascial trigger points and has no established role in diffuse fibromyalgia; it does not address deconditioning, sleep, or central sensitization, and repeated injections are not recommended
  • Tizanidine at bedtime — a central alpha-2 agonist borrowed for muscle spasm and sleep, but it lacks guideline support in fibromyalgia and adds sedation, hypotension, and hepatotoxicity risk
Question 2MusculoskeletalMedium
A 42-year-old woman has proximal muscle weakness and a violaceous rash over the eyelids. Which of the following best explains this disorder?
  • ALower motor neuron degeneration
  • BMitochondrial muscle-energy defect
  • CImmune-mediated inflammatory myopathy
  • DAntibody-mediated neuromuscular blockade
Reveal answer & full explanation
Correct answer: C — Immune-mediated inflammatory myopathy
  • ALower motor neuron degeneration
  • BMitochondrial muscle-energy defect
  • CImmune-mediated inflammatory myopathy✓
  • DAntibody-mediated neuromuscular blockade

Why Immune-mediated inflammatory myopathy is correct

  • Dermatomyositis is an immune-mediated inflammatory myopathy driven by complement-mediated capillary injury.
  • Symmetric proximal weakness plus the heliotrope (violaceous eyelid) rash and Gottron papules are pathognomonic.
  • It is confirmed by elevated muscle enzymes and carries an increased occult-malignancy risk in adults.

Why the others are wrong

  • Antibody-mediated neuromuscular blockade — Myasthenia gravis causes fatigable weakness with ocular and bulbar predominance and no rash (right-category-wrong-target).
  • Lower motor neuron degeneration — Motor neuron disease produces weakness with atrophy and fasciculations but no inflammatory skin findings (weakness-without-rash trap).
  • Mitochondrial muscle-energy defect — Mitochondrial myopathy gives exercise intolerance and lactic acidosis, not an autoimmune heliotrope rash (mechanism mismatch).
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Side-by-side comparison

FeatureFibromyalgiaPolymyositis and Dermatomyositis
At a glanceCentralized 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 presentationDiffuse 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 labs2016 revised fibromyalgia criteria (Wolfe et al.): 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); the diagnosis is valid irrespective of other diagnoses, so coexisting RA, SLE, or OA does not exclude it.; Goal is to exclude…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 perifascicular atrophy with perimysial and perivascular…
ImagingGenerally 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 treatmentPatient 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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Full outlines

Fibromyalgia Polymyositis and Dermatomyositis All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.