Polymyositis Dermatomyositis

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POLYMYOSITIS (PM) AND DERMATOMYOSITIS (DM)

  • Polymyositis
    • clinical picture is dominated by inflammation of striated muscle, causing proximal muscle weakness.
  • Dermatomyositis
    • When the skin is involved it is called ‘dermatomyositis’.
  • Adult polymyositis
    • Women are affected three times more commonly than men.
    • cardinal symptom is proximal muscle weakness.
    • shoulder and pelvic girdle muscles may become wasted but are not usually tender.
    • Face and distal limb muscles are not usually
    • Movements such as squatting and climbing stairs become difficult.
    • As the disease progresses, involvement of pharyngeal, laryngeal and respiratory muscles can lead to dysphonia and respiratory failure
  • Adult dermatomyositis
    • more common in women.
    • Muscle weakness
    • these patients often suffer from myalgia, polyar- thritis and Raynaud’s phenomenon
    • DM is primarily distinguished from PM by the characteristic rash.
      • This typically affects the eyelids
      • heliotrope (purple) discoloration is accompanied by periorbital oedema,
    • Purple-red raised vasculitic patches
      • occur on fingers
      • Gottron’s papules
        • These patches occur over the knuckles (Gottron’s papules) in 70% of patients
        • this appearance is highly specific for DM.
      • Ulcerative vasculitis and calcinosis of the subcutaneous tissue occurs in 25% of cases.
      • In the long term, muscle fibrosis and contractures of joints
    • Antisynthetase syndrome
      • variant of PM/DM
      • Twenty to thirty per cent of patients with PM or DM have it
      • antibodies to tRNA synthetase
      • more likely to develop
        • pulmonary interstitial fibrosis
        • Raynaud’s phenomenon
        • arthritis
        • hardening and fissuring of skin over the pulp surface of the fingers (mechanic’s hands)(MCQ)
      • often has a poor outcome.
    • Respiratory muscles are affected in PM/DM
      • this compounds the effects of interstitial fibrosis.
    • Dysphagia
      • is seen in about 50% of patients
      • owing to oesophageal muscle
    • Association with other ARD (e.g. SLE, RA and SSc)
    • Association with malignancies
      • The associated cancer may not become apparent for 2–3 years
      • recurrent or refractory DM should prompt a search for occult malignancy.
      • Malignancy (e.g. lung, ovary, breast, stomach) can also predate the onset of myositis, particularly in males with DM.
    • Childhood dermatomyositis
      • most commonly affects children between the ages of 4 and 10 years.
    • Investigations
      • Serum creatine kinase (CK), aminotransferases, lactate dehydrogenase (LDH) and aldolase
        • usually raised
        • useful guides to muscle damage but may not reflect activity.
      • ESR is usually not raised.
      • Serum autoantibody studies.
        • Anti-nuclear antibody
        • Rheumatoid factor is present in up to 50%
        • myositis-specific antibodies (MSAs)
        • Anti-synthetase antibodies
      • Electromyography (EMG) shows a typical triad of changes with myositis:
        • spontaneous fibrillation potentials at rest
        • polyphasic or short-duration potentials on voluntary contraction
        • salvos of repetitive potentials on mechanical stimulation of the nerve.
      • Needle muscle biopsy
        • fibre necrosis and regeneration
        • inflammatory cell infiltrate with lymphocytes around the blood vessels and between muscle fibres.
      • Treatment
        • Prednisolone is the mainstay of treatment;
        • steroid-sparing agents such as methotrexate, azathioprine, ciclosporin, cyclophosphamide and mycophenolate mofetil
        • Intravenous immunoglobulin therapy (IVIG)
      • Inclusion body myositis
        • idiopathic inflammatory myopathy
        • occur usually in men over 50 years.
        • Weakness of the pharyngeal muscles causes difficulty in swallowing in over 50%.
        • It is a slowly progressive weakness of mainly distal muscles.
        • In contrast to polymyositis, the creatine kinase is only slightly elevated
        • the EMG shows both myopathic and neuropathic
        • muscle biopsy shows
          • inflammation and basophilic rimmed vacuoles
          • diagnostic filamentous inclusions and vacuoles on electron microscopy.
        • A trial of corticosteroids is worthwhile but generally the response is poor.

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