Myositis Flashcards
Define polymyositis
- symmetrical weakness of limb-girdle muscles and anterior neck flexors
- abnormal muscle biopsy
- elevation in serum or skeletal-muscle enzymes
- abnormal EMG
explain the utility of testing CPK
often tested in pts w/ idiopathic inflammatory myopathy, but may be normal and doesn’t correlate well w/ disease activity
explain the utility of EMG and nerve conducting testing in IIM
to differentiate myopathic and neuropathic disorders
to localize affected area and identify site for biopsy
describe EMG changes in inflammatory myopathy
generally, muscle is irritated
- fibrillation at rest
- high-freq repetitive discharges
- polyphasic potentials of short duration and low amplitude
limitations of EMG testing for IIM
10% will have normal EMGs
abnormalities may be limited to paraspinous muscle
neuropathic findings may also be seen in:
- inclusion body myositis,
- myositis w/ anti-SRP antibodies
- myositis and malignancy
MRI shows increased edema in affected area of muscle - marker of inflammation
pathology in polymyositis
cytotoxic CD8+ T lympocytes in muscle fibers - these express CD45RO
ICAM-1 expressed in muscle fibers
endomysial inflammation w/ predominantly CD8 T cells in polymyositis
clinical features of dermatomyositis
same as polymyositis: proximal muscle weakness +
derm findings: heliotrope rash, periorbital edema, Gottron’s sign (MCP, PIP), rash over knees/elbows/medial malleoli, rash on face/neck/upper torso (shawl sign, V-sign), capillary nail fold changes and periungual erythema
shawl sign in dermatomyositis
pathology of dermatomyositis
perimysial inflammation w/ CD4+ T cells
complement deposited of vessels
perimysial inflammation w/ CD4 T cells in dermatomyositis
describe pathologic differences b/t polymyositis and dermatomyositis
what auto-antibodies might you check for in IIM?
ANA (90%)
Jo-1 (20%)
SRP (5%)
Mi-2 (5-10%)
what is the most common extramuscular target organ of IIM?
lungs - interstitial pneumonitis, alveolitis, fibrosis
ENA panel
do an ENA if ANA is positive, b/c more specific
checks:
- Jo-1: most common myositis specific
- SRP: exclusively PM, if pos means severe type
- Mi-2: more common in DM
Anti-synthetase syndrome
PM or DM assoc w/ anti-Jo-1 antibody
strong assoc w/ interstitial lung disease
also, Raynaud’s, arthritis, mechanic’s hands
pulmonary manifestations of IIM
ILD: inflammation –> fibrosis
Muscle weakness –> impaired breathing
Pharyngeal weakness –> aspiration pneumonitis
relationship b/t malignancy and myositis
increased risk of malignancy in pts w/ PM and DM
strongest assoc w/ ovarian, lung, pancreatic, stomach, colorectal cancer
3 subtypes of dermatomyositis
- adult dermatomyositis
- juvenile dermatomyositis
- amyopathic dermatomyositis
clinical features of juvenile dermatomyositis
similar to adult form + vasculitis, lipodystrophy, calcinosis
amyopathic dermatomyositis
typical rash of DM but w/ no muscle involvement
may later develop muscle involvement
may be assoc w/ malignancy (paraneoplastic?)
tx of PM and DM
primary: steroids
maintenance: methotrexate or axathioprine
inclusion body myositis clinical presentation
typically elderly males
weakenss: may be proximal and symmetric, distal, or asymmetric
no response to therapy, slow gradual decline in muscle strength
