Polymyositis and dermatomyositis

Learning objectives

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

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

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

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