Inflammatory myopathy

Question 1

What is a myopathy?

Answer 1

This is a disease of the muscle in which muscle fibres do not function properly, resulting in muscular weakness

Question 2

What main symptom characterises inflammatory myopathies?

Answer 2

Muscle weakness

Question 3

What is polymyositis?

Answer 3

An idiopathic myopathy, caused by an underlying autoimmune condition, resulting in symmetrical, proximal muscle weakness

Question 4

Who is more at risk of developing polymyositis?

Answer 4

Females (2:1)
Ages 40-50

Question 5

What are some pre-disposing factors of polymyositis?

Answer 5

Underlying malignancy
Viral infection (e.g. Coxsackie virus, HIV)

Question 6

Describe the pathophysiology of polymyositis

Answer 6

CD8+ cells and macrophages surround and destroy healthy, non-necrotic muscle fibres
An autoimmune response to nuclear and cytoplasmic autoantigens is detected in around 60-80% of patients

Question 7

How does polymyositis usually present?

Answer 7

This will present with muscle weakness with an insidious onset, worsening over months

The problem is usually symmetrical and often affects the proximal muscles with specific problems such as difficulty brushing hair or climbing stairs

Question 8

What are some other organ features of polymyositis?

Answer 8

Interstitial lung disease
Oesophageal dysplasia
Myocarditis
Fever
Weight loss
Raynaud’s phenomenon

Question 9

What are some clinical signs of polymyositis?

Answer 9

Muscle wastage
Reduced testing of power
>30 seconds sit to stand

Question 10

What is dermatomyositis?

Answer 10

This is a form of polymyositis with added cutaneous presentations

Question 11

What cutaneous presentations occur in dermatomyositis?

Answer 11

Gottron’s sign
Heliotrope rash
Shawl sign

Question 12

What tests are required in polymyositis?

Answer 12

Bloods
Electromyography
MRI
Muscle biopsy

Question 13

What blood tests are required for diagnosis of polymyositis?

Answer 13

Muscle enzymes (e.g. creatinine kinase)
Inflammatory markers
Electrolytes
Calcium
PTH and TSH
Auto-antibodies

Question 14

What are some specific auto-antibodies in polymyositis?

Answer 14

Anti-Jo-1
Anti-SRP

Question 15

What are some non-specific auto-antibodies in polymyositis?

Answer 15

ANA
Anti-RNP

Question 16

What will electromyography show in polymyositis?

Answer 16

Electromyography can show the electrophysiology of the muscles, showing increased fibrillations, abnormal motor potentials and complex repetitive discharges

Question 17

What will muscle biopsy show in polymyositis?

Answer 17

Perivascular inflammation and muscle necrosis

Question 18

What will MRI show in polymyositis?

Answer 18

Muscle inflammation, oedema, fibrosis and calcification

Question 19

What is the first line pharmacological treatment in polymyositis?

Answer 19

Corticosteroids

Question 20

What non-pharmacological management is used in polymyositis?

Answer 20

Occupational therapy
Physiotherapy

Question 21

What medication can be used in polymyositis if 1st line treatment is unsuccessful?

Answer 21

• Immunosuppresants (e.g. Methotrexate, azathioprine)
• IV immunoglobulin
• Biologic therapy (e.g. Infliximab, Etanercept)

Question 22

What is anti-synthetase syndrome?

Answer 22

This is an autoimmune condition caused by antibodies against one of the aminoacyl tRNA synthetase enzymes, resulting in a mixture of conditions

Question 23

What conditions are present in anti-synthetase syndrome?

Answer 23

• Raynaud’s
• Mechanics hands
• Myositis
• Interstitial lung disease
• Polyarthritis

Question 24

What is mechanics hands?

Answer 24

Mechanics hands is the roughening and cracking of the skin surrounding the fingers and hands