Dermatomyositis and Polymyositis

Question 1

What is myositis?

Answer 1

• Rare idiopathic muscle disease that are characterized by inflammation of striated muscle
• Peak age onset 40-50
• M:F similar

Question 2

Symptoms and signs of myositis

Answer 2

• Insidious onset muscle proximal weakness
• Painless
• Present with SOB or rash sometimes
• Raynauds common

Question 3

Diagnostic criteria

Answer 3

• Symmetrical proximal muscle weakness
• Rasied serum muscle enzymes
• Typical electromyographic changes (muscle response to electrical stimulation)
• Biopsy evidence of myositis
• Typical rash of dermatomyositis

Question 4

Polymyositis vs dermatomyositis diagnostic criteria

Answer 4

PM if 3 or more of the first 4 above criteria
DM if rash and 2 or more of first 3 above criteria

Question 5

Investigations for myositis

Answer 5

• Raised inflammatory markers sometimes
• FBC normally normal
• Kidney not affected
• Raised ALT (from muscle) but liver enzymes normal
• MRI signs
• Creatine kinase high

Question 6

Autoimmune antibodies for myositis

Answer 6

• ANA positive 80%
• Anti Jo-1 and Anti Mi2 also being discovered
• Need to ask for extended muscle auto-antibody panel

Question 7

Treatment for myositis

Answer 7

• High dose corticosteroids
• Long term control can be methotrexate or azathioprine
• Can use Rituximab
• IV immunoglobulin

Question 8

Monitoring myositis

Answer 8

• Difficult
• Inflammatory markers and CK often used
• Repeat EMG studies, MRI or biopsy may be needed

Question 9

What is important precaution wise in dermatomyositis?

Answer 9

• Sun protection is important - commonly triggers symptoms as rash is photosensitive
• Hydroxychloroquine can reduce rash

Question 10

Inflammatory markers in myositis

Answer 10

Often NORMAL

Question 11

What can be affected in myositis to cause problems swallowing?

Answer 11

• Upper oesophagus = striated muscle
• = difficulty swallowing if affected
• = potential aspiration pneumonia

Question 12

How can respiratory failure occur?

Answer 12

Diaphragm involvement

Question 13

What do many patients develop alongside myositis relating to lungs?

Answer 13

• Inflammatory lung disease

Question 14

Risk associated wih dermatomyositis especially

Answer 14

Increase risk of malignancy
Esp 2-3yrs before and after diagnosis

Question 15

What does DM rash lead to?

Answer 15

• It is photosensitive
• Often leads to post inflammtory hypo or hyperpigmentation

Question 16

Where is DM rash?

Answer 16

• Initially on light exposed areas eg scalp, face and neck
• Linear plaques on dorsum of hands

Question 17

What are linear plaques on dorsum hand called?

Answer 17

Gottrons papules

Question 18

Other hand signs of DM

Answer 18

• Dilated nail fold capillaries
• Dry, cracked palms and fingers (mechanics hands)

Question 19

Eyes in DM

Answer 19

Periorbital oedema
Violet rash to eyelids (heliotrope rash)
But this is less common

Question 20

Which other autoimmune conditions can develop myositis?

Answer 20

• SLE
• Scleroderma