Myositis Flashcards
What are the categories of myositis and myopathy?
Myositis, idiopathic
Rhabdomyolysis
Drug induced myopathy
Metabolic myopathies
What do you always want to make sure you rule out before giving a diagnosis of myositis?
Polymyalgia rheumatica
What are some of the idiopathic inflammatory myopathies?
- Polymyositis
- Dermatomyositis
- Inclusion body myositis
- Cancer related
- CT vascular disease-related
How do idiopathic inflammatory myopathies present?
Slowly progressive, fixed proximal weakness is the MAIN feature!
- Fatigue
- Elevated CPK
- Aches, cramps, pains after exertion. BUT muscle pain is not the primary feature
What are the extra-musclar manifestations of inflammatory myopathies?
arthritis/raynaud’s pitting edema, pulmonary function decreased
What would you want to monitor for in someone with a diagnosis of inflammatory myopathy?
INCREASED RISK OF malignancy
What are the criteria for polymyositis?
- Symmetrical weakness of limb girdle muscles
- Biopsy shows necrosis/inflammation
- Elevation in serum/skeletal muscle enzymes
- EMG shows fibrillations/sharp waves
- derm findings
What would help you determine whether a patient’s muscle weakness was myopathic or neuropathic?
- Myopathic: proximal+symmetric. Normal neuro exam
- Neuropathic: can be asymmetric/distal.
- Abnormal neuro exam
What are the relevant muscle enzymes?
CPK Aldolase AST ALT LDH **AST and ALT are NOT solely liver enzymes!
What might cause a high CPK level?
- Acute MI
- Racial differences
- Trauma
- Exercise
- Drugs: ETOH, cocaine, statins, AZT
Large muscle mass
What are the weaknesses of using CPK in idiopathic inflammatory mysositis?
CPK can be normal, and does not correlate with disease activity. Could be asymptomatic but have elevated enzymes
What would you use to differentiate between myopathic and neuropathic disorders?
EMG and nerve conduction. In myositis, EMG abnormal, nerve conduction study will be normal
What imaging would you want in myositis
Get an MRI
Describe what types of cells you would see in polymyositis and what cell surface receptors are involved
CD8+ T lymphocytes invade muscle fibers
- CD45RO positive lymphocytes
- ICAM-1 expressed on muscle fibers
How does polymyositis present?
- Gradual onset of fixed weakness in proximal muscle groups
2. Elevated muscle enzymes
What tests/imaging would you want to confirm the diagnosis of polymyositis?
- EMG and MRI
2. Muscle biopsy
Dermatomysositis: What’s different about this from polymyositis?
Think Polymyositis PLUS rash.
- -However, muscle histology is different
- -More likely to be a paraneoplastic syndrome
What are the additional features of dermatomyositis?
- heliotrope discoloration of eyelids
- Periorbital edema
- Gottron’s sign: erythematous rash over MCP and PIP
- Rash over knees, elbows, medial malleoli
- Rash over face, neck, and upper torso
- capillary nailfuld changes + periungual erythema
What is different about the histology of dermatomysitis as opposed to polymyositis?
Dermatomyositis: Inflammation is perivascular, while polymyositis has inflammation centered in the muscle
- B cells predominate with CD4+ cells. In polymyositis, primarily CD8+ T cells and no B cells
- Dermatomyositis has vasculopathy and complement deposition while polymyositis does not
What is the most common auto-antibody in polymyositis and dermatomyositis?
ANA (90%) Sensitive, but not specific
–There’s also: Jo-1, SRP, and Mi-2
What is the most common extramuscular target organ in idiopathic inflammatory myositis?
the LUNGs. Beware of aspiration pneumonitis, alveolitis, fibrosis (ILD)
What does it mean if PM/DM is positive with ANA?
Nothing. It’s congruent with PM/DM but not specific. Could be indicative of another disorder
What does it mean if PM/DM is positive for Ro/La antibodies?
Likely to be secondary to lupus/sjogren’s
What does it mean if PM/DM is positive for Jo-1?
Specific to myositis. Targets anti-histidyl tRNA synthetase
