inflammatory muscle disease Flashcards
what are the main subtypes of idiopathic inflammatory myopathies?
1) dermatomyositis
2) polymyositis
3) inclusion body myositis
4) necrotising auto- immune myositis
inflammatory muscle disease is important to consider in the differential for…
subacute muscle weakness
what procedures aid diagnosis in inflammatory muscle disease?
history/family history
examination-pattern of muscle weakness
blood tests: creatine kinase and autoantibodies
EMG and NCD
open muscle biopsy
which muscles can be weak in inflammatory myopathies?
proximal muscles:
upper limbs
lower limbs
neck
trunk
sometimes bulbar muscles
sometimes respiratory muscles
what EMG features are present in polymyositis?
complex repetitive discharges on needle insertion
fibrillations on resting
loow amp-short duration, polyphasic spikes on insertion.
what is dermatomyositis?
most common inflammatory myopathy in children
a complement-mediated muscle and skin disease affecting first the intracellular capillaries
what are the symptoms and signs for dermatomyositis
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
what is the main type of treatment for dermatomyositis
immunosuppressive treatment.
describe the pathogenesis behind dermatomyositis
b cell mediated antibodies
against capillary membrane
leads to vasculopathy
leads to ischaemia of muscle fibres
and atrophy in the periphery
what are the signs and symptoms of polymyositis?
proximal weakness (neck trunk shoulder and hip)
elevated creatine kinase
how is polymyositis diagnosed?
clinical picture and muscle biopsy (essential)
by exclusion (no single diagnostic test)
pattern of muscle weakness
ck level
emg findings
histology
describe the pathogenesis of polymositis
cd8+ t-cell mediated attack on muscle cells which have upregulated MHC-1 expression.
what histological features are associated with polymyositis
inflammatory infiltrate
invasion of non-necrotic fibres
MHC upregulation
visible mononuclear t cells surrounding and invading non-necrotic fibres
what is inclusion body myositis
a myopathy affecting adults
most common cause of acquired myopathy in patients over the age of 50yrs
has a characteristic pattern of muscle weakness
what is the pathology of inclusion body myositis?
complex
inflammatory muscle features similar to polymyositis
but also: superimposed degenerative changed characterised by the presence of vacuoles and amyloid related misfolded proteins.
weakness of what muscle groups is characteristic of inclusion body myositis?
finger flexors
quadriceps
tibialis anterior
what degenerative features are present in inclusion body myopathy?
rimmed vacuoles
intracellular congophilic deposits
what is necrotising auto-immune myopathy?
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
what causes of necrotising auto-immune myopathy have been identified?
cancer
viral infection
exposure to statins
considered likely to be an antibody mediated disease.
what is the pathogenesis of necrotising auto-immune myopathy?
muscle fibre necrosis mediated by macrophages
necrotic muscle fibres invaded by macrophages
antigen remains unknown
what is the treatment for inflammatory muscle disease?
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
what may be useful for treating dermatomyositis?
rituximab. as it depleted b cells.
TNF may also be helpful
what is polymyositis?
a t cell mediated disease where cytotoxic CD8+ cells invade MCH-1 expressing muscle fibres
