Learning objectives

• Definition of polymyositis and dermatomyositis
• Management of polymyositis and dermatomyositis

Definition and mechanisms

• Myositis is the name for a group of rare conditions such as polymyositis and dermatomyositis, leading to weak, painful, or aching muscles
• Polymyositis and dermatomyositis are autoimmune myopathies characterized by inflammation and weakness of proximal skeletal muscles 
• Characteristically there is a rise in serum enzymes derived from muscle, e.g. creatine phosphokinase (CPK) and myoglobin may be released leading to myoglobinuria
• Dermatomyositis, unlike polymyositis, is associated with a variety of characteristic skin manifestations
• The cause is unknown, maybe an immune reaction triggered by a virus or tumor
• Both occur almost two times more often in women than in men
• It can occur at any age

Signs and symptoms

• Both polymyositis and dermatomyositis have symptoms in common with sclerosis or sometimes systemic lupus erythematosus:
  • Muscle weakness
  • Contraction of the arms and legs
  • Shortness of breath
  • Difficulty swallowing
  • Muscle tenderness or pain
  • Raynaud’s phenomenon
  • Fever
  • Feeling tired
  • Weight loss
• If dermatomyositis occurs along with polymyositis, symptoms may also include:
  • Skin rash
  • Swelling around the eye
  • Swelling at the base and sides of the fingernails
  • Splitting of the skin of the fingers

Diagnosis

• Laboratory findings:
  • Elevations in serum creatine kinase, lactate dehydrogenase, aldolase, and aminotransferases
  • Myositis-specific autoantibodies
• Muscle biopsy
• Electromyogram
• MRI

Treatment

• Corticosteroids
• Immunosuppressive drugs: methotrexate, cyclophosphamide, chlorambucil, azathioprine, cyclosporine
• Immunoglobulin therapy
• Exercise is important to reduce swelling and to build or restore muscle strength

Management

Suggested reading

• Christopher-Stine L, Vleugels An Amato AA. 2022 Clinical manifestations of dermatomyositis and polymyositis in adults. Up To Date. 
• Pollard BJ, Kitchen, G. Handbook of Clinical Anaesthesia. Fourth Edition. CRC Press. 2018. 978-1-4987-6289-2.
• Raychaudhuri SP, Mitra A. Polymyositis and dermatomyositis: Disease spectrum and classification. Indian J Dermatol. 2012;57(5):366-370.
• Dalakas MC, Hohlfeld R. Polymyositis and dermatomyositis. Lancet. 2003;362(9388):971-982.