Rheumatic Diseases of Skeletal Muscle Flashcards
Types of Myopathies
- Polymyositis
- Dermatomyositis (amyopathic and juvenile)
- inclusion body myositis
- cancer related myositis
- collagen vascular disease related myositis
Clinical manifestations of inflammatory myopathies
- slowly progressive, fixed proximal muscle weakness
- premature fatigue
- elevated muscle CPK
- post-exertional aches, cramps and pains (chronic myalgias not a primary feature)
Risk factors of inflammatory myopathies
- increased risk of malignancy
- may have arthritis, raynaud’s, pitting edema of the extremities, , pulmonary involvement
Criteria for defining polymyositis
- symmetrical weakness of limg-girdle muscles and anterior neck flexors
- muscle biopsy evidence of necrosis of Type 1 and 2 fibers, phagocytosis, regeneration, variation in fiber type with inflammatory exudation. –> confirm dignaosis
- elevation of serum or skeletal muscle enzymes
- EMG triad of short, small, polyphasia motor units, fibrillations and sharp waves; and bizarre, repetitive discharges
- dermatologic features
Classes of Muscle weakness
Myopathic = proximal and symmetric. Remainder of neuro exam is normal.
Neuropathic = proximal, distal and/or asymmetric. Other abnormalities on neuro exam.
List types of muscle enzymes you would measure in a patient presenting with muscle weakness
- CPK (most commonly measured)
- aldolase
- AST, ALT and LDH
What are potential etiology of high CPK levels?
- acute MI
- racial differences - african americans have higher.
- trauma = sharp, blunt; EMG needle, biopsy
- exercise = anaerobic, aerobic
- drugs = ETOH, cocaine, statins, AZT
- Carrier = glycogen storage disease, muscular dystrophy, periodic paralysis, malignant hyperthermia
- large muscle mass
- asymptomatic (benign) hyper-CK-emia
Muscle enzymes in inflammatory myopathies
- CPK is most commonly followed
- CPK can be normal
- CPK is elevated at some point in every patient
- none of these enzymes correlate well with disease activity.
- Enzymes can be elevated and people can be asymptomatic
What is the use of EMG and Nerve conduction studies?
- Differentiate myopathic and neuropathic disorders
- helps further localize the affected area
- identify appropriate site for biopsy
What are the electrophysiologic changes in inflammatory myopathies?
- fibrillation at rest
- increased insertional activity
- bizarre high-frequency repetitive discharges
- polyphasic potentials of short duration and low amplitude
- spontaneous and positive sharp waves
What are typical patterns of EMG in inflammatory myopathies?
- 40% have classic features
- normal in 10%
- abnormalities may be limited to paraspinous muscles
- neuropathic findings may also be seen in = inclusion body myositis, myositis with anti-SRP antibodies, myositis and malignancy
MRI findings in inflammatory myopathies
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Polymyositis
- Cytotoxic CD8 invading muscle fiber
- invading lymphocytes express CD45Ro (antigen primed memory cells)
- ICAM-1 expressed on muscle fibers
Components of muscle histology in polymyositis?
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Definition of dermatomyositis
polymyositis plus a rash
muscle histology is different
May be more like a paraneoplastic phenomenon
Features of Dermatomyositis
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Classic Rashes and nail findings in Dermatomyositis
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tissue findings in dermatomyositis
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