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Dermatomyositis & Polymyositis

Idiopathic inflammatory myopathies causing symmetric proximal muscle weakness, elevated muscle enzymes, characteristic autoantibodies, and in dermatomyositis pathognomonic skin findings

Review date
reviewed 2026-05-04
Reading time
7 min read
Author
Dr Kola Tytler MBBS CertHE MBA MSt MRCGP
Musculoskeletal & Rheumatologyless-commonlong-term-condition
On this page
Condition details
Musculoskeletal & Rheumatology
less-common
7 min read
reviewed 2026-05-04
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About This Page

This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.

Key points

  • Inflammatory myopathy causes symmetric proximal weakness, not primarily pain
  • Dermatomyositis has heliotrope rash and Gottron papules
  • CK and aldolase are usually elevated
  • Major complications: ILD, dysphagia/aspiration, myocarditis, malignancy
  • Adult dermatomyositis requires malignancy screening

Overview

Dermatomyositis and polymyositis are idiopathic inflammatory myopathies with progressive proximal muscle weakness. Dermatomyositis includes characteristic cutaneous disease and malignancy association.

Epidemiology

Rare disorders. Dermatomyositis occurs in adults and children; polymyositis is less common than historically thought because mimics are frequently reclassified.

Clinical Features

Symptoms
Difficulty climbing stairs or rising from chair
Difficulty lifting arms overhead
Myalgias but weakness predominates
Dysphagia or aspiration symptoms
Dyspnea or dry cough suggesting ILD
Weight loss or night sweats suggesting malignancy
Signs
Objective proximal weakness with preserved sensation
Heliotrope rash
Gottron papules/sign
Shawl sign or V-sign photosensitive rash
Bibasilar crackles suggesting ILD

Investigations

First-line
Focused clinical assessmentPattern recognition, red flags, functional impact, and targeted examination
Basic labs when indicatedCBC, CMP, ESR/CRP, CK, urinalysis, or disease-specific testing depending on suspected condition
Initial imaging when indicatedPlain radiographs or MRI/ultrasound based on suspected structural, inflammatory, infectious, or neurologic disease
Second-line
Disease-specific confirmatory testingAutoantibodies, HLA-B27, synovial fluid, nerve conduction studies, DEXA, or cultures as appropriate
MRI/ultrasound/CTUsed for early inflammatory disease, occult fracture, tendon tear, infection, or surgical planning
Screening before immunosuppressionTB, hepatitis, vaccination review, and baseline labs when biologic or high-risk therapy is planned
Specialist
Specialist referralRheumatology, orthopedics, infectious disease, ophthalmology, neurology, or spine surgery depending on red flags and disease severity

Management

ACR/EULAR Inflammatory Myopathy Classification Framework and Expert Treatment Consensus
1
Initial management
  • Address red flags and emergencies first
  • Use guideline-directed first-line therapy matched to disease severity
  • Educate the patient and set functional goals
  • Use analgesia and rehabilitation when appropriate
2
Escalation
  • Escalate to specialist-directed therapy if severe, refractory, progressive, or organ-threatening disease
  • Use imaging, procedures, immunosuppression, antibiotics, or surgery according to diagnosis
  • Monitor response objectively and revise diagnosis if response is atypical
3
Prevention and follow-up
  • Manage comorbidities and medication toxicity
  • Vaccinate and screen when immunosuppression is used
  • Prevent disability, falls, fracture, infection, and functional decline

Complications

  • Functional impairment: Pain, weakness, stiffness, deformity, or disability depending on disease
  • Diagnostic delay: Missed infection, fracture, inflammatory disease, neurologic compromise, or organ-threatening complication
  • Medication toxicity: NSAID, steroid, antibiotic, anticoagulation, opioid, or immunosuppressive adverse effects
  • Chronic disease burden: Reduced quality of life, work impairment, deconditioning, and mental health impact
USMLE Step 2 CK Exam Tips
  • 1Proximal weakness + high CK = inflammatory myopathy
  • 2Heliotrope rash and Gottron papules = dermatomyositis
  • 3Adult dermatomyositis requires cancer screening
  • 4Anti-Jo-1 + ILD + mechanic hands = antisynthetase syndrome
  • 5PMR has normal CK and pain/stiffness without true weakness
  • 6AST/ALT can rise from muscle injury

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Verified Sources & References

ACR/EULAR Inflammatory Myopathy Classification Framework and Expert Treatment Consensus
ACR Clinical Practice Guidelines
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