muscle diseases 2
Terms
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- what two troups are dz of muscle divided into?
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1. neurogenic= distal wekaness, no pain, fasciculations present
2. myopathic= proximal weakness, +/- pain, no fasciculations - what characterizes neurogenic m. dz?
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1. distal weakness
2. no pain
3. fasciculations present - what characterizes myopathic m. dz?
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1. proximal weakness
2. +/- pain
3. no fasciculations - what is duchenne's muscular dystrophy?
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1. x-linked lack of dystrophin
2. progressive proximal weakness and wasting beginning at age 1 yr
3. increased CPK
4. calf hypertrophy
5. Gower's maneuver - what are si/sx of duchenne's muscular dystrophy?
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1. progressive proximal weakness and wasting
2. beginning at age 1 yr
3. increased creatine phosphate kinase
4. calf hypertrophy
5. waddling gait
6. Gower's maneuver (pts pick themselves off the floor by using arms to help legs) - what is Becker's dystrophy?
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1. dystrophin levels are generally normal in Becker's, but protein qualitity of dystrophin is altered
2. may have nml lifespan, unlike Duchenne type (death occurs in 10-20s) most often d/t pneuomonia - what else characterizes duchenne muscular dystrophy?
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1. intellectual retardation
2. skeletal deformities
3. m. contractures
4. cardiac involvment
5. increased CPK - what often occurs with polymyositis?
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1. dermatomyositis
2. b/l proximal m. weakness - what are si/sx of polymyositis/dermatomyositis?
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1. symmetric weakness/atrophy of proximal limb m.
2. cutaneous manifestation in dermatomyositis (Gottron's sign= scaly patches over the dorsum of proximal IP and MCP jts, periungual erythema, dilations of nailbed capillaries)
3. m. aches
4. dysphonia (laryngeal m. weakness)
5. dysphagia - what does dermatomyositis present with?
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1. polymyositis
2. periorbital heliotropic red to purple rash
3. Gottron's sign= scaly patches over the dorsum of proximal IP and MCP jts - what is dx for polymyositis and dermatomyositis?
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1. positive ANA
2. increased creatine kinase and aldolase (muscle nzs)
3. m. bx--shows inflamm changes - what is myasthenia gravis (MG)?
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1. autoantibodies block the postsynaptic acetylcholine receptor
2. pts present with ptosis, diplopia, difficulty chewing/swallowing, respiratory difficulites, limb weakness - what may be a/c thymomas, throid and outher autoimmune dz (e.g. lupus, RA)?
- 1. myasthenia gravis (autoAbs blocking the postsynaptic acetylcholine receptor)
- what are sx of myasthenia gravis?
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1. m/c in women in 20-30s or men in 50-60s
2. m. weakness worse with use, diplopia, dysphagia,
3. proximal limb weakness which can progress to cause respiratory failure - what is the dx for myasthenia gravis?
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1. trial of edrophonium (short-acting anticholinesterase) causes an immediate increase in strength
2. confirm c/ electromyelography--repetitive stimulation causes a decrease in action potential - what is pathopys of myasthenia gravis?
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1. autoAbs binding to Ach receptors--cause m. weakness, ocular palsies, ptosis
2. when given a shrot acting anticholinesterase (edrophonium, neostigmine), m. weakness improves - what is lambert-eaton syndrome?
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1. autoAb to PRE-synaptic Ca channels seen c/ small cell lung CA
2. causes defective release of Ach - how does MG differ from Lambert-Eaton?
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Lambert-Eaton:
1. sx imporve c/ m. use
2. action potential strength increases with repeated stimulation
MG:
1. activity increases weakness of affected m.
2. repetitive stimulation decreases the action potential - what CA is Lambert-Eaton a/c?
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1. small cell lung CA
2. defective release of Ach in response to a nerve impluse - what happens with aminoglycosides in MG?
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1. aminoglycoside abx prevent the release of Ach from nerve endings
2. are particularly dangerous in pts with prexisting disturbances of neuromuscular transission (e.g. MG) - what is tx for MG?
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1. anticholinesterase inhibitors (e.g. pyridostigmine) 1st line
2. steroids, cyclophosphamide, azathioprine for severe dz
3. plasmapheresis temporarily alleviates sx by removing the Ab
4. resection of thymoma can be curative