Dermatomyositis

Question 1

Definition of dermatomyositis

Answer 1

Inflammatory disorder causing symmetrical, proximal muscle weakness and characteristic skin lesions

Question 2

Epidemiology of dermatomyositis

Answer 2

-May be idiopathic or associated with connective tissue disorders or underlying malignancy (typically ovarian, breast and lung cancer, found in 20-25% - more if patient older). Screening for an underlying malignancy is usually performed following a diagnosis of dermatomyositis
-Polymyositis is a variant of the disease where skin manifestations are not prominent

Question 3

Skin features of dermatomyositis

Answer 3

-Photosensitive
-Macular rash over back and shoulder
-Heliotrope rash in the periorbital region
-Gottron’s papules - roughened red papules over extensor surfaces of fingers
-‘Mechanic’s hands’: extremely dry and scaly hands with linear ‘cracks’ on the palmar and lateral aspects of the fingers
-Nail fold capillary dilatation

Question 4

Other features of dermatomyositis

Answer 4

-Proximal muscle weakness +/- tenderness
-Raynaud’s
-Respiratory muscle weakness
-Interstitial lung disease: e.g. Fibrosing alveolitis or organising pneumonia
-Dysphagia, dysphonia

Question 5

Investigations of dermatomyositis

Answer 5

-Majority of patients (around 80%) are ANA positive
-Around 30% of patients have antibodies to aminoacyl-tRNA synthetases (anti-synthetase antibodies), including:
=antibodies against histidine-tRNA ligase (also called Jo-1)
=antibodies to signal recognition particle (SRP)
=anti-Mi-2 antibodies

Question 6

Management of dermatomyositis

Answer 6

-IV corticosteroid
-Methotrexate, azathioprine
-IV immunoglobulin