Inflammatory Myositis Flashcards
What are the common clinical features of inflammatory myositis
?
- symmetrical, progressive proximal muscle weakness and/or pain
- difficulty climbing stairs, getting out of the car, standing from seated
- difficulty raising arms above head, combing hair - constitutional symptoms may be present
What is the epidemiology?
Rare 5-10 cases/1 million
More common in african americans
F:M, 2:1
mean age of onset 30-50
What is the pathogenesis of polymyositis?
Autoimmune T cell mediated cytotoxic process against muscle Ags
CD8+ T cells and macrophages invade muscle fibres
What is the link between Myositis and malignancy?
Incidence ~ 15%
Presents within 2 years of initial Dx
increased with anti-TIF1-gamma
mainly adenocarcinomas
What are the characteristic features of Dermatomyositis?
Heliotrope rash (face) Gottron's papules V-neck sign Shawl sign periungal changes - dilated nail bed capillary loops - erythema mechanics hands
What is the pathophysiology of Dermatomyositis?
Myopathy differs from polymyositis as it is complement mediated
humeral attack against muscle capillaries and small arterioles
Activation of C3 -> formation of MAC
Capillaries are destroyed and muscles undergo microinfarction
CD4 postive T-cells
What diagnostic tests are performed?
- CK - raised 5-50 times
- EMG - abnormal in 90%
- decreased amplitude of motor potentials
- fibrillation
- complex repetitive discharges - auto antibodies
- myositis specific
- CTD associated - Muscle biopsy
- MRI - increased STIR signal indicated oedema due to inflammation - helps to guide site for biopsy
What does the muscle biopsy show in polymyositis?
chronic inflammatory infiltrate surrounding the muscle fibres
variation in muscle fibre size
damaged fibres
What myositis specific antibodies are found?
Anti-Jo-1
- associated with anti-synthetase syndrome
- associated with poor prognosis
Anti-Mi2
- associated with typical skin lesions of dermatomyositis
anti-TIF1-gamma and anti-NXP2 are associated with malignancy
Anti-SRP antibodies
- poor prognostic marker, increased cardiac involvement
What are the different types of inflammatory myositis?
Polymyositis Dermatomyositis CTD associated myositis Inclusion body myositis Juvenile dermatomyositis
What are some Ddx for myositis?
Drugs - statins, alcohol Endocrine myopathies - hyper/hypothyroidism Metabolic myopathies Muscular dystrophies Infectious Paraneoplastic syndrome neuropathy Diabetic neuropathy
What investigations should be performed to exclude malignancy in myositis?
FOB
mammography
pelvic USS in women
CT CAP usually done
What does the anti-synthetase syndrome comprise of?
anti-Jo-1 myopathy fever ILD Raynaud's arthritis mechanics hands
What myositis associated auto antibodies can be found?
ANA
anti-Scl
- associated with polymositis/ scleroderma overlap
anti-SnRP
- Associated with myositis/connective tissue overlap
anti Ro/La
- associated with Sjogrens and SLE
What is the typical pattern of clinical presentation of inclusion body myositis?
- insidious onset of distal arm and proximal leg weakness
- asymmetric
- dysphagia is common with established disease
What is the epidemiology of inclusion body myositis?
elderly men affected most commonly
20-30% have concomitant autoimmune disease
What does the muscle biopsy show in inclusion body myositis?
endomysial inflammation
rimmed vacuoles
intracellular amyloid deposits
What drugs can cause myopathy?
- Alcohol
- Antimalarials
- Colchicine
- Azole antifungals
- Statins
- D-penicillamine
- Vincristine
- AZT
What antibody is associated with autoimmune necrotising myositis caused by statins?
anti-HMGCR
- antibody against HMGCR - the target of statins
- disease continues despite stopping the statin
What is the treatment for dermatomyositis skin disease?
o Sun avoidance, sunscreen o Topical steroids o Antimalarials (Doxycycline) o MTX o Mycophenalate
How is myositis managed?
- initial treatment - steroids
- if weakness is severe use 3-5 days IV steroids
- 1-2 month taper - If responds to steroids consider steroid sparing medication
- AZA, MTX, Mycophenalate, Cyclosporine - If disease does not respond to steroids (30%)
- IVIg - If does not respond to steroids + IVIg
- ? diagnosis
- Rituximab
- Initial management is high dose steroids and MTX then add in IVIg if not doing well
What idiopathic inflammatory myopathy is most associated with malignancy?
Dermatomyositis = 30%
Polymyositis = 15%
Inclusion body - no association with malignancy
What are the most common cancers associated with Dermatomyositis/polymyositis?
Ovarian - main one
Cervix, lung, pancreas, bladder, stomach
Factors indicating higher likelihood of malignancy?
Older age rapid onset Skin necrosis peri-ungal erythema low C4 levels low lymphocyte counts
Which myopathy is the least responsive to treatment?
Inclusion body myositis
Which myopathy is most associated with humoral immunity?
Dermatomyositis
Which myopathy is most associated with T-cell mediated immunity?
Polymyositis
Inclusion body myositis
Elevations of CK in which inflammatory myopathies?
Polymyositis/dermatomysitis have modest elevations
IBM has mild or normal CK
