Dermatomyositis & Polymyositis

Question 1

What are dermatomyositis and polymyositis?

Answer 1

Rare idiopathic muscle diseases characterized by inflammation of striated muscle

M:F ratio is similar and peak age of onset is 40-50 years.

Question 2

What is a common symptom of dermatomyositis and polymyositis?

Answer 2

Insidious onset of proximal muscle weakness, often painless
- difficulty standing from a chair, climbing stairs or lifting overhead

Presentation may also include shortness of breath or rash.

Question 3

What syndrome is commonly associated with dermatomyositis?

Answer 3

Raynaud’s syndrome

This syndrome involves episodes of reduced blood flow to the fingers and toes.

Question 4

What are the diagnostic criteria for polymyositis?

Answer 4

• symmetrical proximal muscle weakness
• raised serum muscle enzyme levels
• typical EMG changes
• biopsy evidence of myositis
• typical rash of dermatomyositis

PM is diagnosed if >= 3 of the first 4 criteria are met.

DM if rash and >=2 of the first 3

Question 5

What are the diagnostic criteria for dermatomyositis?

Answer 5

Typical rash of dermatomyositis and >= 2 of the first 3 criteria for polymyositis

DM is diagnosed if a rash is present along with muscle weakness and enzyme elevation.

Question 6

What might some patients with dermatomyositis and polymyositis show in laboratory tests?

Answer 6

Raised inflammatory markers

The full blood count (FBC) is usually normal.

Question 7

What is a clue indicating muscle damage in laboratory tests?

Answer 7

Raised ALT (from muscle) with normal liver enzymes

This can suggest muscle involvement rather than liver damage.

Question 8

What percentage of patients with dermatomyositis and polymyositis are antinuclear antibody positive?

Answer 8

80%

Specific auto-antibodies like anti-Jo-1 and anti-Mi2 are increasingly discovered.

Question 9

What imaging technique can demonstrate myositis?

Answer 9

MRI

MRI is useful for assessing muscle inflammation.

Question 10

What is the mainstay treatment for dermatomyositis and polymyositis in the first few weeks?

Answer 10

High dose corticosteroids

Monitoring disease activity can be challenging.

Question 11

What are some long-term treatments for dermatomyositis and polymyositis?

Answer 11

Methotrexate (MTX), Azathioprine (AZA), Rituximab, Intravenous immunoglobulin

Sun-protection and hydroxychloroquine (HCQ) may also help in DM.

Question 12

True or False: Many patients with dermatomyositis have elevated inflammatory markers.

Answer 12

False

Many patients may have normal inflammatory markers.

Question 13

What complication can occur due to diaphragmatic involvement in myositis?

Answer 13

Respiratory failure

This can be a serious consequence of muscle weakness affecting respiratory muscles.

Question 14

What risk is associated with dermatomyositis?

Answer 14

Increased risk of malignancy

This is particularly significant in the 2-3 years before and after diagnosis.

Question 15

What characterizes the rash associated with dermatomyositis?

Answer 15

Photosensitive, often leads to hyper- or hypo-pigmentation

The rash typically appears in sun-exposed areas e.g. scalp, face, neck

Question 16

Fill in the blank: The rash in dermatomyositis takes the form of _______.

Answer 16

linear plaques on the dorsal aspects of the hands (Gottron’s papules)

Other features may include dilated nail-fold capillaries and dry, cracked palms.

Question 17

What is the less common rash associated with dermatomyositis that affects the eyelids?

Answer 17

Heliotrope rash (violet rash to the eyelids)

Periorbital edema is also common in this condition.

Question 18

Patients with which conditions can develop myositis?

Answer 18

Scleroderma and systemic lupus erythematosus (SLE)

These conditions can overlap with myositis symptoms.

Question 19

How can dermatomyositis disease activity be monitored

Answer 19

• repeat EMG studies
• MRI or biopsy

Question 20

Why might swallowing be affected in patient with DM/PM

Answer 20

Upper oesophagus has striated male so may be risk of aspiration pneumonia

Question 21

what are 4 potential skin changes in dermatomyositis

Answer 21

• Gottron lesions (scaly erythematous patches) on the knuckles, elbows and knees
• Heliotrope rash (a purple rash on the face and eyelids)
• Periorbital oedema (swelling around the eyes)
• Photosensitive erythematous rash on the back, shoulders and neck

Polymyositis occurs without skin features

Question 22

what is the critical test for myositis

Answer 22

CK
- usually less than about 300 IU/L but with myositis, the result is often in the multiples of thousands

Question 23

give 5 causes of raised CK

Answer 23

• Rhabdomyolysis
• Acute kidney injury
• Myocardial infarction
• Statins
• Strenuous exercise

Question 24

what is the most common myositis-specific antibody associated with polymyositis

Answer 24

anti-Jo-1 antibodies