Dermatomyositis

Question 1

what is it?

Answer 1

clinically similar to polymyositis other than the addition of typical cutaneous features

Question 2

what are the typical cutaneous features?

Answer 2

Gottron’s papules
Heliotrope rash
V-shaped rash over the chest

Question 3

what are the investigations?

Answer 3

as for polymyositis
raised inflammatory markers
CK raised often 10x normal
Immunology
- ANA, anti-RNP: shared with other AI diseases
- Anti-Jo-I, anti-SRP: unique to myositis
MRI
- localize extent of muscle involvement
- show signal intensity abnormalities of muscle due to inflammation, oedema, scarring
EMG
- abnormal
muscle biopsy - crucial
- excluding other rare muscle diseases
- muscle fibres in varying stages of inflammation, necrosis, regeneration

Question 4

what does dermatomyositis have an associated risk of?

Answer 4

malignancy

• 25% of patients
• greatest in the 5 years following diagnosis
• common cancers: breast, ovarian, lung, colon, oesophagus, bladder
• should screen for malignancy at diagnosis