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Dermatomyositis

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Dermatomyositis

Dr. Muhammad Farooq

Introduction

  • Dermatomyositis is an idiopathic inflammatory myopathy.
  • Characterised by progressive muscle weakness and distinctive skin manifestations.
  • Occurs in both adults and children.
  • Associated with malignancy in adults.

Epidemiology

  • Rare disorder (incidence ~1 per 100,000).
  • More common in females.
  • Peak incidence: 5–15 years (juvenile) & 45–65 years (adults).

Pathophysiology

  • Autoimmune-mediated microangiopathy.
  • Complement activation leads to destruction of capillaries.
  • Muscle ischemia and perifascicular atrophy.
  • Inflammatory infiltration in perimysium. Z
  • Genetic factors play some role.
  • More common in HLA-DR people.

Clinical Features

Muscle Manifestations

  • Symmetrical proximal muscle weakness.
  • Difficulty climbing stairs, rising from chair, lifting arms.
  • Muscle pain (less prominent than weakness).
  • Dysphagia in severe cases.
  • Speech problems are rare.

Skin Manifestations

  • Heliotrope rash: Violaceous discoloration around eyelids.
  • Gottron’s papules: Erythematous scaly papules over knuckles.
  • Photosensitivity rash on face, neck, upper chest.
  • Mechanic’s hands: Rough, cracked skin on palms.
  • Shawl sign: Erythematous rash over shoulders, upper back, and neck (V-shaped distribution).

Clinical Images

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Investigations

Blood Tests

  • Creatine Kinase (CK): Elevated
  • AST/ALT: Elevated
  • LDH: Elevated

Autoantibodies

  • Anti-Mi-2
  • Anti-TIF1-Îł (malignancy association)

Electrophysiology

  • EMG: Myopathic pattern

Imaging

  • MRI: Muscle edema

Muscle Biopsy

  • Perifascicular atrophy
  • Perimysial inflammation z

Histopathological Comparison

Perimysial Inflammation in Dermatomyositis

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Pathological features showing perimysial inflammation - characteristic of dermatomyositis.

Endomysial Inflammation in Polymyositis

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Pathological features showing endomysial inflammation - characteristic of polymyositis for comparison.

Association with Malignancy

  • Strong link in adults (up to 30%).
  • Common cancers:
    • Ovarian
    • Breast
    • Lung
    • Gastric
  • Cancer screening is essential in all adult patients.

Systemic Manifestations

Pulmonary Involvement

  • Interstitial lung disease
  • Shortness of breath
  • Restrictive pattern on spirometry

Cardiac Involvement

  • Arrhythmias
  • Cardiomyopathy

Musculoskeletal

  • Joint pain (arthritis, arthralgia)

General Symptoms

  • Fatigue
  • Fever
  • Weight loss

Treatment

  • First-line: Corticosteroids (prednisolone)
  • Immunosuppressants: Methotrexate, Azathioprine
  • Biologic/Immunomodulatory therapies: IVIG or Rituximab in resistant cases
  • Physiotherapy: To prevent contractures
  • Sun protection: For skin lesions

Prognosis

  • 5-year survival rate: ~75–80%.
  • Worse prognosis if associated with malignancy.
  • Juvenile cases may develop calcinosis.
  • Early diagnosis and treatment improve outcomes.

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Summary

  • Dermatomyositis is an autoimmune inflammatory myopathy with skin involvement.
  • Presents with proximal muscle weakness and characteristic rashes (heliotrope rash, Gottron’s papules, shawl sign, mechanic’s hands).
  • Associated with malignancy in adults (up to 30%) - requires cancer screening.
  • Diagnosis: CK elevation, autoantibodies (Anti-Mi-2, Anti-TIF1-Îł), muscle biopsy showing perifascicular atrophy and perimysial inflammation.
  • Treatment: Steroids, immunosuppressants, physiotherapy.
  • Prognosis: 5-year survival ~75-80%; depends on early detection and malignancy screening.

Graph View

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