Inflammatory Myopathies Flashcards
What is the definition of inflammatory myopathies?
myopatheis where the inflammatory response is directed against
- normal muscle
- supporting stroma
- an dmuscle as one of many tissues
all inflammation in muscle is NOT an “autoimmune” inflammatory myopathy
What are the disease that can be classified as an inflammatory myopathy?
polymyositis
dermatomyositis
inclusion body myositis (major rule out)
What is the general presentation of inflammatory myopathies?
can be caused by other things than inflammation such as muscular dystrophies
proximal weakness - symmetric in hip and shoulder muscles
relative lack of pain - not a predominant feature
other inflammation - skin, joint, interstitial lung
What are the laboratory findings of inflammatory myopathies?
elevated Creatinine Kinase (CK or CPK)
serologic tests ESR, ANAA, CRP may be increased
EMG (electromyography) abnormalities but NCS (nerve conduction studies) usually ok
muscle biopsy
What is the role of creatinine kinase in the body?
needed for energy access in the muscle
marker of muscle damage (>200 is concerning)
high percent by weight protein - 81 kD
What are the general features of polymyositis?
symmetric, proximal greater than distal
progresses over months - if hyperacute think antibody against signal recognition particle couple with pain
F>M, high ESR and CK
pain in 30% especially if with other CTD - scleroderma with Scl-1 Ab and MCTD (Ab to RNP, Raynaud) or SLE
What are the primary signs of pulmonary involvement in polymyositis?
separate class of disorder - often idiopathic
anti Jo-1 antibody (histidyl t-RNA)
sarcoid usually present
female more often than male
associated with HIV
What are some of the clinical manifestations of anti Jo-1 antibody?
myalgias
seronegative arthritis
occult fever
What is a key finding in EMG for polymyositis?
the finding of neuropathic findings like fibrillations and positive waves in the proximal muscles
happens if there is patchy inflammation part of myofiber separated form the NMJ
What is the histopathology of polymyositis?
inflammation around normal muscle fibers
scattered necrosis, degeneration, regeneration
internal nuclei
variability of fiber size but seldom any hypertrophy
multifiocal, so biopsy weak but not wasted
What is the treatment of polymyositis?
corticosteroids - prednisone or IV solumedrol (to start, may need to switch over to other drugs to prevent side effects)
azathioprine
methotrexate
cyclosporine
all of these take time - may take up to 6 months for maximal effect
What are the general findings in dermatomyositis?
proximal weakness
dysphagia
skin problems
What are the skin findings in dermatomyositis?
sun exposed areas - erythema
face and eyelids - may be violaceous and edema
eczema on extensor surface of joints - MCP, elbows, knees, sacrum
What are additional findings in juvenile dermatomyositis?
in addition to skin there are contractures at ankles (toe walking)
calcinosis (subcutaneous, tends to be late in course of disease)
may get a vasculitis with GI involvement
What is the histopathology of dermatomyositis?
membrane attack complex at normal appearing capillaries
perivascular inflammation
perifascicular atrophy (pathomneumonic) - may be more apparent on ATPase then H&E stain
occasionally 10% there is no muscle pathology despite obvious skin damage
What is the histopathology of IBM?
rimmed vacuoules - seen on H&E but sometimes more apparent on Gomori Trichrome
vacuoles contain beta amyloid, may need Congo Red to prove
can see 15 to 18 mm filaments on EM
stain with TDP-43
light microscopy usually good enough for diagnosis
