Dermatomyositis and Polymyositis Flashcards
What is dermatomyositis and polymyositis?
Rare idiopathic muscle disease that are characterised by insidious onset of progressive symmetrical muscle weakness and autoimmune-mediated striated muscle inflammation.
Epidemiology of DM and PM.
Some sources say that it is more common in women than in men
Some sources say it is similar in both sexes.
The general consensus seems to be that it is more common in women.
Peak age of onset is 40-50 years.
Symptoms of these idiopathic inflammatory myopathies.
Insidious onset of proximal muscle weakness.
It is often painless but can be associated with myalgia and arthralgia.
Patient might also be SOB or have a rash.
Raynaud’s syndrome can be seen as well.
What is the difference between polymyositis and dermatomyositis?
Dermatomyositis is polymyositis + the skin signs.
Additional symptoms in dermatomyositis.
Photosensitive erythematous rash on back, shoulders and neck. Macular rash (1)
Lilac-purple heliotrope rash on eyelids (3)
Nailfold erythema (4)
Gottron’s papules (2)
Myalgia, polyarthritis and Raynaud’s is more common in DM as well.
However the distinguishable factor is usually a rash.
Extra-muscular signs in PM and DM.
Fever
Arthralgia
Raynaud’s
ILD
Myocarditis
Arrhythmias
Investigations done in PM and DM.
Some might have raised inflammatory markers - however a lot of patients markers are normal.
FBC usually normal
Creatine kinase raised.
Kidneys are not affected
Raised ALT
Antibody screening
MRI
Muscle biopsy will establish a definitive diagnosis
EMG
Screening for malignancy.
Why is ALT raised in PM and EMG?
Not due to liver damage but because of muscle damage.
What antibody markers can be found in PM and DM?
ANA positive
anti-Jo1 and anti-Mi2 in 80% of cases
Why is it important to screen for malignancy in PM and DM?
Especially in DM.
This is becasue there is an increased risk of malignancy especially in 2-3 years before and after the diagnosis of DM.
It is difficult to establish whether the malignancy is due to DM, or DM is due to malignancy.
DM and PM may be a paraneoplastic phenomenon due to lung, pancreatic, ovarian, bowel or breast malignancy.
Why might there be an increased risk of aspiration pneumonia in PM and DM?
Because the upper oesophagus has striated muscle
This means that swallowing may be affected.
Later signs in PM and DM.
Dysphagia, dysphonia due to muscle weakness.
Respiratory weakness and resp failure due to diaphragmatic involvement.
Where does the DM rash usually initially appear?
Because it is photosensitive it usually appears first in light exposed areas such as the scalp, face and neck.
It leads to post inflammatory hyper or hypopigmentation.
What might PM and SM be secondary to?
Malignancy
Scleroderma
SLE
Diagnostic criteria of PM and DM.
Symmetrical proximal muscle weakness
Raised serum muscle enzyme levels
Autoantibodies suggestive of PM and DM
Typical electromyographic (EMG) changes
Biopsy evidence of myositis
Typical rash of dermatomyositis
