Dermatomyositis/Polymyositis

Question 1

What is the difference between myositis, polymyositis and dermatomyositis?

Answer 1

Myositis = inflammation of striated muscle
Polymyositis = inflammation and necrosis of skeletal muscle fibres
Dermatomyositis = inflammation and necrosis of striated muscle fibres AND skin

Question 2

What is myositis?

Answer 2

Inflammation of striated muscle.

Question 3

What is polymyositis (PM)?

Answer 3

A rare muscle disorder of unknown aetiology in which there is inflammation and necrosis of skeletal muscle fibres.

Question 4

What is dermatomyositis?

Answer 4

A rare disorder of unknown aetiology. There is inflammation and necrosis of skeletal muscle fibres and skin.

Question 5

Give 3 symptoms of dermatomyositis.

Answer 5

1. Rash.
2. Muscle weakness.
3. Lungs are often affected too e.g. ILD.

Question 6

What are the features of polymyositis? Give 3.

Answer 6

1. Progressive symmetrical proximal muscle weakness with myalgia ± arthralgia.
2. Difficulty squatting, going upstairs, rising from a chair & raising hands above the head.
3. Muscle weakness of pharyngeal, laryngeal + respiratory muscles = lead to dysphagia, dysphonia (difficulty speaking) & respiratory failure.

Question 7

Give 3 features of dermatomyositis.

Answer 7

1. Macular rash
2. Lilac-purple rash + heliotrope discolouration of the eyelids with oedema
3. Nailfold erythema
4. Roughened red papules over knuckles/elbows/knees
   - Scaly erythematous plaques over the knuckles (Gottron’s papules)
5. Subcutaneous calcification
6. Arthralgia, dysphagia resulting from oesophageal muscle involvement and Raynaud’s phenomenon

Question 8

Give 3 extra-muscular signs of polymyositis/dermatomyositis.

Answer 8

1. Fever
2. Arthralgia
3. Raynaud’s
4. Interstitial lung fibrosis
5. Myocardial involvement

Question 9

Outline the investigations done to diagnose polymyositis/dermatomyositis.

Answer 9

1. Muscle biopsy
2. Muscle enzymes
3. Serum antibodies
4. Electromyography (EMG)
5. MRI

Question 10

What would a muscle biopsy show for polymyositis / dermatomyositis?

Answer 10

Muscle biopsy:
* Shows fibre necrosis and inflammatory cell infiltrates - CONFIRMS DIAGNOSIS

Question 11

What investigation is needed to confirm a diagnosis of polymyositis/dermatomyositis?

Answer 11

Muscle biopsy

Question 12

What would a blood test for muscle enzymes show in a patient with polymyositis / dermatomyositis?

Answer 12

Muscle enzymes in the plasma are ALL raised:
1. Serum creatine kinase (CK)
2. Aminotransferases - ALT + AST
3, Lactate dehydrogenase (LDH)
4. Aldolase

Question 13

What would a blood test for autoantibodies show for polymyositis / dermatomyositis?

Answer 13

Serum antibodies:

• Antinuclear antibody (ANA) positive in DM
• Rheumatoid factor positive in 50%
• Myositis-specific antibodies (MSAs) - Anti-Mi2 and Anti-Jo1

Question 14

What would an EMG detect for polymyositis / dermatomyositis?

Answer 14

Electromyography (EMG) to detect typical muscle changes

Question 15

What would a MRI detect for polymyositis / dermatomyositis?

Answer 15

MRI can detect abnormally inflamed muscles

Question 16

How would you manage polymyositis/dermatomyositis?

Answer 16

1. Oral prednisolone
2. EARLY INTERVENTION with steroid sparing immunosuppressive therapy is
   useful when there is clinical relapse:
   - Oral Azathioprine/Methotrexate/Ciclosporin.
3. Bed rest may be helpful but must be combined with an exercise programme.
4. HYDROXYCHLOROQUINE or TOPICAL TACROLIMUS may help with skin
   disease
5. Screen for malignancy