Dermatomyositis & Polymyositis Flashcards
What are dermatomyositis and polymyositis?
Rare idiopathic muscle diseases characterized by inflammation of striated muscle
M:F ratio is similar and peak age of onset is 40-50 years.
What is a common symptom of dermatomyositis and polymyositis?
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.
What syndrome is commonly associated with dermatomyositis?
Raynaud’s syndrome
This syndrome involves episodes of reduced blood flow to the fingers and toes.
What are the diagnostic criteria for polymyositis?
- 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
What are the diagnostic criteria for dermatomyositis?
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.
What might some patients with dermatomyositis and polymyositis show in laboratory tests?
Raised inflammatory markers
The full blood count (FBC) is usually normal.
What is a clue indicating muscle damage in laboratory tests?
Raised ALT (from muscle) with normal liver enzymes
This can suggest muscle involvement rather than liver damage.
What percentage of patients with dermatomyositis and polymyositis are antinuclear antibody positive?
80%
Specific auto-antibodies like anti-Jo-1 and anti-Mi2 are increasingly discovered.
What imaging technique can demonstrate myositis?
MRI
MRI is useful for assessing muscle inflammation.
What is the mainstay treatment for dermatomyositis and polymyositis in the first few weeks?
High dose corticosteroids
Monitoring disease activity can be challenging.
What are some long-term treatments for dermatomyositis and polymyositis?
Methotrexate (MTX), Azathioprine (AZA), Rituximab, Intravenous immunoglobulin
Sun-protection and hydroxychloroquine (HCQ) may also help in DM.
True or False: Many patients with dermatomyositis have elevated inflammatory markers.
False
Many patients may have normal inflammatory markers.
What complication can occur due to diaphragmatic involvement in myositis?
Respiratory failure
This can be a serious consequence of muscle weakness affecting respiratory muscles.
What risk is associated with dermatomyositis?
Increased risk of malignancy
This is particularly significant in the 2-3 years before and after diagnosis.
What characterizes the rash associated with dermatomyositis?
Photosensitive, often leads to hyper- or hypo-pigmentation
The rash typically appears in sun-exposed areas e.g. scalp, face, neck
Fill in the blank: The rash in dermatomyositis takes the form of _______.
linear plaques on the dorsal aspects of the hands (Gottron’s papules)
Other features may include dilated nail-fold capillaries and dry, cracked palms.
What is the less common rash associated with dermatomyositis that affects the eyelids?
Heliotrope rash (violet rash to the eyelids)
Periorbital edema is also common in this condition.
Patients with which conditions can develop myositis?
Scleroderma and systemic lupus erythematosus (SLE)
These conditions can overlap with myositis symptoms.
How can dermatomyositis disease activity be monitored
- repeat EMG studies
- MRI or biopsy
Why might swallowing be affected in patient with DM/PM
Upper oesophagus has striated male so may be risk of aspiration pneumonia
what are 4 potential skin changes in dermatomyositis
- 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
what is the critical test for myositis
CK
- usually less than about 300 IU/L but with myositis, the result is often in the multiples of thousands
give 5 causes of raised CK
- Rhabdomyolysis
- Acute kidney injury
- Myocardial infarction
- Statins
- Strenuous exercise
what is the most common myositis-specific antibody associated with polymyositis
anti-Jo-1 antibodies
