inflammatory muscle disease

Question 1

what are the main subtypes of idiopathic inflammatory myopathies?

Answer 1

1) dermatomyositis
2) polymyositis
3) inclusion body myositis
4) necrotising auto- immune myositis

Question 2

inflammatory muscle disease is important to consider in the differential for…

Answer 2

subacute muscle weakness

Question 3

what procedures aid diagnosis in inflammatory muscle disease?

Answer 3

history/family history

examination-pattern of muscle weakness

blood tests: creatine kinase and autoantibodies

EMG and NCD

open muscle biopsy

Question 4

which muscles can be weak in inflammatory myopathies?

Answer 4

proximal muscles:

upper limbs
lower limbs
neck
trunk

sometimes bulbar muscles
sometimes respiratory muscles

Question 5

what EMG features are present in polymyositis?

Answer 5

complex repetitive discharges on needle insertion

fibrillations on resting

loow amp-short duration, polyphasic spikes on insertion.

Question 6

what is dermatomyositis?

Answer 6

most common inflammatory myopathy in children

a complement-mediated muscle and skin disease affecting first the intracellular capillaries

Question 7

what are the symptoms and signs for dermatomyositis

Answer 7

symmetrical proximal muscle weakness +rash

(heliotrope rash on face, sun exposed areas and extensor joint surfaces)

(gottron paplues )

creatine kinase usually elevated

may be associated with oesophageal, pulmonary and cardiac disease.

in adults associated with malignancies

Question 8

what is the main type of treatment for dermatomyositis

Answer 8

immunosuppressive treatment.

Question 9

describe the pathogenesis behind dermatomyositis

Answer 9

b cell mediated antibodies

against capillary membrane

leads to vasculopathy

leads to ischaemia of muscle fibres

and atrophy in the periphery

Question 10

what are the signs and symptoms of polymyositis?

Answer 10

proximal weakness (neck trunk shoulder and hip)

elevated creatine kinase

Question 11

how is polymyositis diagnosed?

Answer 11

clinical picture and muscle biopsy (essential)

by exclusion (no single diagnostic test)

pattern of muscle weakness
ck level
emg findings
histology

Question 12

describe the pathogenesis of polymositis

Answer 12

cd8+ t-cell mediated attack on muscle cells which have upregulated MHC-1 expression.

Question 13

what histological features are associated with polymyositis

Answer 13

inflammatory infiltrate
invasion of non-necrotic fibres
MHC upregulation

visible mononuclear t cells surrounding and invading non-necrotic fibres

Question 14

what is inclusion body myositis

Answer 14

a myopathy affecting adults

most common cause of acquired myopathy in patients over the age of 50yrs

has a characteristic pattern of muscle weakness

Question 15

what is the pathology of inclusion body myositis?

Answer 15

complex

inflammatory muscle features similar to polymyositis

but also: superimposed degenerative changed characterised by the presence of vacuoles and amyloid related misfolded proteins.

Question 16

weakness of what muscle groups is characteristic of inclusion body myositis?

Answer 16

finger flexors
quadriceps
tibialis anterior

Question 17

what degenerative features are present in inclusion body myopathy?

Answer 17

rimmed vacuoles

intracellular congophilic deposits

Question 18

what is necrotising auto-immune myopathy?

Answer 18

myopathy that usually presents with rapidly developing muscle weakness (acute/subacute)

an overlooked acute/subacute inflammatory myopathy mediated by macrophages and possibly autoantibodies that may respond to immunotherapy

Question 19

what causes of necrotising auto-immune myopathy have been identified?

Answer 19

cancer
viral infection
exposure to statins

considered likely to be an antibody mediated disease.

Question 20

what is the pathogenesis of necrotising auto-immune myopathy?

Answer 20

muscle fibre necrosis mediated by macrophages

necrotic muscle fibres invaded by macrophages

antigen remains unknown

Question 21

what is the treatment for inflammatory muscle disease?

Answer 21

target antibodies remain unknown- so only non–specific imunnosupressants

with steroids and steroid sparing agents such as azathioprine, methotraxate ad cyclosporin

agents to protect bones and stomach for those on long term steroids

IV ig

Question 22

what may be useful for treating dermatomyositis?

Answer 22

rituximab. as it depleted b cells.

TNF may also be helpful

Question 23

what is polymyositis?

Answer 23

a t cell mediated disease where cytotoxic CD8+ cells invade MCH-1 expressing muscle fibres