• Dermatomyositis is an idiopathic inflammatory myopathy with proximal weakness and characteristic cutaneous findings.
  • It has biphasic peaks. Seen in children aged 7-15 years and adults aged 30-50 years.
  • It is more predominant in females.


  • Dermatomyositis is mediated by Type 1 interferon cytokine family (IFN alpha, IFN beta)
  • Classic antibodies associated are anti-Mi-2 against helicase and anti-Jo-1 (antisynthetase antibody).
  • Muscle pathology involves injury to muscle capillaries and perifascicular atrophy (injury to muscle fibers at the end of muscle fascicles).
  • Skin pathology involves injury to the basal layer of keratinocytes.


  • Gottron’s sign/papules: Violaceous lesions that can be flat (Gottron sign) or raised (Gottron papules) over dorsal metacarpophalangeal and interphalangeal joints of the hands, elbows, knees.
  • Heliotrope rash: Violaceous periorbital macular erythema with or without edema.
  • Butterfly-shaped, malar erythematous rash (note that malar refers to its site: the cheek and butterfly refers to its shape).
    • It crosses the nasolabial folds because this distinguishes it from the malar rash of systemic lupus erythematosus, which spares the nasolabial folds.
  • Erythema and poikiloderma on the photo exposed areas –
    • On the Chest (V SIGN)
    • On the Shoulder, Neck, Back (THE SHAWL SIGN)
  • Calcinosis cutis, which is aberrant calcium depositions in the skin and subcutaneous tissues, which cause yellowish or white dermal lesions and stiffening with finger joint immobility.

  • Symmetric proximal muscle weakness (muscle weakness when combing hair, reaching for objects overhead, rising from a seated position, climbing stairs).
  • Extensor muscles are more often affected than the flexor muscles.
Systemic Manifestations
  • Dysphagia, GERD
  • Myocarditis
  • Interstitial lung disease
  • Dysphonia
  • Subcutaneous calcifications (Calcinosis cutis)
  • Flexion contracture of the ankles (tip toe gait in children)
  • Malignancies are common in adults, maybe related to cross reacting autoantigens in the muscle and on tumor cells: Most common malignancies are adenocarcinoma (Ovarian, lung, stomach, pancreatic, colorectal).


  1. Diagnostic skin involvement (Gottron’s papule, Heliotrope rash) or diagnostic muscle biopsy findings (Perifascicular atrophy)


  1. All of the following –
  • Suggestive skin involvement
  • Subacute or chronic proximal or distal weakness
  • Muscle biopsy showing perimysial or perivascular inflammation without features suggesting another disorder OR skin biopsy showing interface dermatitis along with clinical exclusion of SLE.


  • Elevated Creatine phosphokinase(CPK) generally 10 times the upper limit or normal but can vary (↑↑CPK)
  • Abnormal Aldolase and LDH (↑Aldolase and ↑LDH)
  • Antibody studies(anti-Mi 2, anti-Jo-1, anti-MDA5)
  • ↑ALT & ↑AST


  • MRI, EMG


  • Skin biopsy (interface dermatitis)
  • Muscle biopsy (Perifascicular atrophy, Perivascular and Perimysial inflammation)




  • Corticosteroids are the first line( typically Prednisolone 1mg/kg/day orally until significant improvement occurs and then gradual taper).
  • Second line are Methotrexate, azathioprine, cyclosporine, IVIG.
Non pharmacological
  • Avoid sun exposure
  • Physical therapy.

Ref: Goldman-Cecil Medicine, Medscape, Uworld, Drawittoknowit, Amboss

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