Polymyositis and Dermatomyositis

In station 5 you may be asked to assess a patient with weakness (and a rash).

HISTORY (3 minutes)

  • Muscle weakness
    • Timing (sudden/gradual, progression, intermittent/constant, previous episodes, since when, worse at particular time of day)
    • Which muscles (proximal/distal, uni/bilateral)
      • Proximal: Rising from a chair, going up stairs, lifting, brushing hair,
      • Distal: doing buttons, writing (should be spared in polymyositis)
    • Any change in your voice, any difficulty swallowing/breathing
    • Any facial weakness, any change in vision (not in polymyositis), any eyelid drooping
    • Neuro Q: sensation etc.
  • Muscle pain/ache/cramp (usually not in polymyositis)
  • Skin: Rashes, nail changes, photosensitivity
  • Systemic features (extramuscular/dermatological)
    • Constitutional: tiredness, weight loss, anorexia, fever, sweats
    • Joint pains/swelling/stiffness
    • Resp: SOB, CP, cough
    • GI: reflux, bowels, abdo pain
    • Cardiac: CP, palps, syncope, ankle swelling
  • Extra connective tissue disease questions:
    • Raynauds, hair loss, ulcers, dry eye/mouth, red eye etc.
  • Assess for cancer eg:
    • Breast checks
    • Haemoptysis
    • Jaundice, abdo pain, bloating
    • PR bleeding/PV bleeding
    • Lumps/bumps
  • Exclude Polymyalgia rheumatica (pain and stiffness) and Giant cell arteritis: headache, scalp pain, jaw pain on chewing, visual disturbance
  • PMH: connective tissue disease/joint problem/autoimmune problem, recent infections, cancer, diabetes/thyroid, renal/liver
  • Fx: connective tissue disease, autoimmune problem, muscle problem
  • Dx: statins, steroids
  • Sx: alcohol, occupation


EXAMINE (3 minutes)

  • Power (MRC grade) and palpate muscles for bulk and tenderness. Ask patient to rise from sitting with arms crossed
  • Full neuro examination including neck flexion/extension, cranial nerves (especially CNs 3,4,6,7) and fatiguability check
  • Skin: face, trunk, hands and nails, limbs
  • Systemic: Lymph nodes, CVS, Resp, Abdo, Thyroid. Offer Breast exam, PR, PV if indicated.
  • Joints (synovitis)
  • Palpate temporal arteries if suspicion of GCA from history
  • Any evidence of autoimmune disease eg. vitiligo, diabetes etc or other connective tissue disease eg. scleroderma, lupus
  • Patient may appear Cushingoid from steroid use.

ICE and Explanation (2 minutes)



Polymyositis: 50-60 mean age of onset. Inflammation of skeletal muscle fibres.

Dermatomyositis: 5-15 year olds, 45-65 year olds (polymyositis and rash)

Females> males

Proximal motor weakness

  • Gradual onset, symmetrical, progressive
  • Shoulder, neck, pelvis. Can get dysphonia, dysphagia, SOB
  • Not eye/face/distal muscles
  • Minimal pain



  • Heliotrope rash and oedema: eyelids, nasolabial folds, malar region, forehead
  • Gottrans papules: flat/raised, purple-red papules on knuckles, extensor surfaces eg. elbows, knees
  • V sign rash- chest and neck
  • Shawl sign rash- shoulders and proximal arms. Exacerbated by sunlight.
  • Holster sign rash- proximal thighs laterally
  • Mechanics hands- radial side of index finger
  • Nailfold abnormalities- periungal erythema, dilated capillary loops


  • Constitutional symptoms
  • MSK: arthralgia/arthritis
  • Resp: Interstitial lung disease, aspiration pneumonia, pulmonary hypertension
  • GI: oesophageal dysmotility, reflux, rectal incontinence
  • Cardiac: dysrhythmia, heart block, myocarditis
  • Vascular: raynauds, skin ulcers

Association with Cancer:

  • 10-20%
  • >50% if over 65 years old
  • Dermatomyositis > polymyositis
  • Usually within 3 years of myositis onset
  • Breast, lung, pancreas, stomach, colon, ovary, lymphoma
  • Cancer screen: FOB, CXR, mammogram, abdo/pelvic CT, tumour markers (PSA, CEA, CA125, CA19-9, CA15-3). If negative, rescreen in 3-5 years. Annual examination.

Antisynthetase syndrome (anti-jo-1):

  • Myositis
  • Interstitial lung disease
  • Raynauds
  • Symmetrical nonerosive small joint arthritis
  • Mechanics hands
  • Occasional fever

Differential diagnosis of “weakness”:

  1. Neuromuscular: cord/plexus/root/nerve/NMJ (eg. myasthenia gravis, motor neuron disease, Guillain Barre syndrome)
  2. Muscular (myopathies)
    1. Inflammatory: polymyositis/dermatomyositis. NB: can overlap with other connective tissue disease eg mixed connective tissue disease
    2. Other connective tissue disease eg. SLE, vasculitis, RA, systemic sclerosis.
    3. Cancer (paraneoplastic: carcinomatous neuromyopathy)
    4. Drugs (statins, steroids)
    5. Infections (bacterial infections, HIV, CMV, EBV, Hepatitis)
    6. Endocrine (thyroid, addisons, osteomalacia, cushings, acromegaly, diabetic amyotrophy)
    7. Toxins (alcohol)
    8. Metabolic (renal/liver failure, electrolyte disturbance)
    9. Miscellaneous (inclusion body myositis, rhabdomyolysis, sarcoidosis, mitochondrial myopathy, muscular dystrophy)
  3. Other (not true weakness)
    1. Polymyalgia rheumatica (pain and stiffness) +/- giant cell arteritis
    2. Fibromyalgia (pain, fatigue, stiffness, sleep disturbance)
    3. OA/rotator cuff problem (muscular atrophy and weakness secondary to joint pain)
    4. Fatigue/malaise/depression




  • Bloods
    • Routine (FBC, U+E, LFT, Ca, P, Mg)
    • Rheumatological screen: ESR (normal/increased), CRP (normal usually), ANA (50-80%), ANCA, RF, anti-CCP, ‘myositis blot’ (myositis associated antibodies eg. anti-RNP, Anti-Pm-Scl, Anti-Ku, anti-Ro) and myositis specific antibodies eg. antisynthetase/anti-jo-1, anti-SRP, anti Mi2), immunoglobulins, complement
    • CK, AST, ALT, LDH (all raised)
    • TFTs, vitamin D and bone profile, HBa1C, cortisol, HIV, Hepatitis screen, CMV/EBV/adenovirus, serum ACE
  • Urine dip and urine PCR
  • Nerve conduction studies (normal) and EMG (myopathic changes)
  • MRI muscle eg. thigh (inflamed muscle)
  • Muscle biopsy eg. thigh (inflammation) +/- skin biopsy
  • Cancer screen: FOB, CXR, mammogram, CT, tumour markers (PSA, CEA, CA125, CA19-9, CA15-3)
  • Joint xray/USS
  • Systemic assessment: ECG, CXR, Echo, lung function tests, HRCT, OGD/colonoscopy/barium swallow



Dermatology review, avoid sunshine, suncreams

Rheumatology review



Steroids- prednisolone high dose (60mg) daily. Monitor power and CK. Gastro and bone protection.  Once in remission taper and monitor for recurrence

Steroid-sparing agents: methotrexate, azathioprine, mycophenolate mofetiil, cyclophosphamide



Treat malignancy


Written by Dr Sarah Kennedy


Resources used to write this document include those listed in the references section of this webpage and also:


Rheumatology Secrets by Sterling West