Inflammatory Myositis

Question 1

What are the common clinical features of inflammatory myositis
?

Answer 1

1. 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
2. constitutional symptoms may be present

Question 2

What is the epidemiology?

Answer 2

Rare 5-10 cases/1 million
More common in african americans
F:M, 2:1
mean age of onset 30-50

Question 3

What is the pathogenesis of polymyositis?

Answer 3

Autoimmune T cell mediated cytotoxic process against muscle Ags
CD8+ T cells and macrophages invade muscle fibres

Question 4

What is the link between Myositis and malignancy?

Answer 4

Incidence ~ 15%
Presents within 2 years of initial Dx
increased with anti-TIF1-gamma
mainly adenocarcinomas

Question 5

What are the characteristic features of Dermatomyositis?

Answer 5

Heliotrope rash (face)
Gottron's papules
V-neck sign
Shawl sign
periungal changes
- dilated nail bed capillary loops
- erythema
mechanics hands

Question 6

What is the pathophysiology of Dermatomyositis?

Answer 6

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

Question 7

What diagnostic tests are performed?

Answer 7

1. CK - raised 5-50 times
2. EMG - abnormal in 90%
   - decreased amplitude of motor potentials
   - fibrillation
   - complex repetitive discharges
3. auto antibodies
   - myositis specific
   - CTD associated
4. Muscle biopsy
5. MRI - increased STIR signal indicated oedema due to inflammation - helps to guide site for biopsy

Question 8

What does the muscle biopsy show in polymyositis?

Answer 8

chronic inflammatory infiltrate surrounding the muscle fibres
variation in muscle fibre size
damaged fibres

Question 9

What myositis specific antibodies are found?

Answer 9

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

Question 10

What are the different types of inflammatory myositis?

Answer 10

Polymyositis
Dermatomyositis
CTD associated myositis
Inclusion body myositis
Juvenile dermatomyositis

Question 11

What are some Ddx for myositis?

Answer 11

Drugs
- statins, alcohol
Endocrine myopathies
- hyper/hypothyroidism
Metabolic myopathies
Muscular dystrophies
Infectious
Paraneoplastic syndrome
neuropathy
Diabetic neuropathy

Question 12

What investigations should be performed to exclude malignancy in myositis?

Answer 12

FOB
mammography
pelvic USS in women
CT CAP usually done

Question 13

What does the anti-synthetase syndrome comprise of?

Answer 13

anti-Jo-1
myopathy
fever
ILD
Raynaud's
arthritis
mechanics hands

Question 14

What myositis associated auto antibodies can be found?

Answer 14

ANA
anti-Scl
- associated with polymositis/ scleroderma overlap
anti-SnRP
- Associated with myositis/connective tissue overlap
anti Ro/La
- associated with Sjogrens and SLE

Question 15

What is the typical pattern of clinical presentation of inclusion body myositis?

Answer 15

• insidious onset of distal arm and proximal leg weakness
• asymmetric
• dysphagia is common with established disease

Question 16

What is the epidemiology of inclusion body myositis?

Answer 16

elderly men affected most commonly

20-30% have concomitant autoimmune disease

Question 17

What does the muscle biopsy show in inclusion body myositis?

Answer 17

endomysial inflammation
rimmed vacuoles
intracellular amyloid deposits

Question 18

What drugs can cause myopathy?

Answer 18

• Alcohol
• Antimalarials
• Colchicine
• Azole antifungals
• Statins
• D-penicillamine
• Vincristine
• AZT

Question 19

What antibody is associated with autoimmune necrotising myositis caused by statins?

Answer 19

anti-HMGCR

• antibody against HMGCR - the target of statins
• disease continues despite stopping the statin

Question 20

What is the treatment for dermatomyositis skin disease?

Answer 20

o	Sun avoidance, sunscreen
o	Topical steroids
o	Antimalarials (Doxycycline)
o	MTX
o	Mycophenalate

Question 21

How is myositis managed?

Answer 21

1. initial treatment - steroids
   - if weakness is severe use 3-5 days IV steroids
   - 1-2 month taper
2. If responds to steroids consider steroid sparing medication
   - AZA, MTX, Mycophenalate, Cyclosporine
3. If disease does not respond to steroids (30%)
   - IVIg
4. 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

Question 22

What idiopathic inflammatory myopathy is most associated with malignancy?

Answer 22

Dermatomyositis = 30%
Polymyositis = 15%
Inclusion body - no association with malignancy

Question 23

What are the most common cancers associated with Dermatomyositis/polymyositis?

Answer 23

Ovarian - main one

Cervix, lung, pancreas, bladder, stomach

Question 24

Factors indicating higher likelihood of malignancy?

Answer 24

Older age
rapid onset
Skin necrosis
peri-ungal erythema
low C4 levels
low lymphocyte counts

Question 25

Which myopathy is the least responsive to treatment?

Answer 25

Inclusion body myositis

Question 26

Which myopathy is most associated with humoral immunity?

Answer 26

Dermatomyositis

Question 27

Which myopathy is most associated with T-cell mediated immunity?

Answer 27

Polymyositis

Inclusion body myositis

Question 28

Elevations of CK in which inflammatory myopathies?

Answer 28

Polymyositis/dermatomysitis have modest elevations

IBM has mild or normal CK