Dermatomyositis

Overview

Dermatomyositis is a connective tissue disease characterised by autoimmune inflammation of the skin muscles. It may be idiopathic or associated with connective tissue disease or malignancy.

Epidemiology

• Peak age of presentation of 50 years
• Peak age of onset in children is around 5-10 years
• Twice as common in women than in men

Risk Factors & Associations

• Female sex
• Black ethnicity
• UV radiation
• Malignancy

Presentation

Features consist of those seen in myositis along with skin involvement

Skin features:

• Extremely dry and scaly hands with linear cracks on the palmar and lateral aspects of the fingers
  • This is also known as “mechanic’s hands”
• Pruritus
• Gottron’s papules may be present – rough and red papules over the fingers’ extensor surfaces
• Macular rash over back and shoulder
• Heliotrope periorbital rash
• Photosensitive skin

Myositis features:

• Diffuse weakness in the proximal muscles
• Onset is over weeks or months and progression is steady
• Distal muscles are usually spared
  • They are usually affected late in the disease
• Pharyngeal weakness may cause dysphagia or dysphonia
• There are no skin manifestations
• 1/3 of patients have pain
• Extraocular muscles are unaffected
• Patients may have difficulty holding their head up

Investigations

• Serum creatine kinase (CK):
  • Raised
• Serum aldolase:
  • Raised
  • Lower sensitivity than creatine kinase (CK)
• Muscle biopsy may show:
  • Perivascular or inter-fascicular inflammation
  • Endothelial hyperplasia in the intramuscular blood vessels
  • Perifascicular atrophy
• EMG – not essential for diagnosis if CK and muscle biopsy findings are positive
• Anti-Mi-2 antibodies
  • Positive
• Around 30% of patients have anti-synthetase antibodies

Management

Patients should be screened for malignancy.

In combined muscle and skin disease

• 1^st line: oral corticosteroid initial therapy + photoprotection + treatment of skin disease + treatment of underlying malignancy
• 2^nd line: methotrexate or azathioprine + photoprotection + treatment of skin disease + treatment of underlying malignancy
• 3^rd line: other immunosuppressants e.g. ciclosporin

In skin disease alone

• 1^st line: topical corticosteroids e.g. hydrocortisone/betamethasone/clobetasol
  • Combined with moisturisers and photoprotection
• 2^nd line: hydroxychloroquine
• 3^rd line: immunosuppressants e.g. methotrexate

Monitoring

• Patients should have regular reviews to monitor muscle strength and biomarkers of disease activity
• Patient should be assessed for the development of cardiac or pulmonary involvement
• Patients should be monitored for malignancy
  • Screening should be done at presentation and if no malignancy is found, annually for 3 years following diagnosis
• Patients should be monitored for drug toxicity and adverse effects

Patient Advice

• Patients should use high-factor sunscreen to protect themselves from UV radiation
• Patients should participate in physiotherapy
• Patients should be counselled on adverse effects and monitoring of the drugs involved in their treatment

Complications

• Respiratory tract infections
  • Due to respiratory muscle weakness
• Interstitial lung disease
• Cardiac disease
• Dysphagia
• Malignancy
• Cutaneous calcinosis

Prognosis

• Associated malignancy indicates a poorer prognosis
• Around 20-40% of patients will achieve remission
• Mortality is 2-3 times higher than the general population with cancer, lung, and cardiac complications and infections being the most common causes of death