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Neurology > NMJ and Muscle disorders > Flashcards

NMJ and Muscle disorders Flashcards

1
Q

what distinguishes a LMN lesion from a UMN one

A

weakness
low tone
fasiculations

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2
Q

what part of spinal cord to motor neurones arise from

A

ventral horn

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3
Q

what do the terminal projections of motor neurones do

A

give rise to very fine projections that run along the muscle cell
synapse at motor end plate

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4
Q

how many motor neurones can a muscle respond to

A

only one

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5
Q

what is between the motor neurone and muscle

A

synaptic cleft/ gutter

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6
Q

describe transmission at the NMJ

A

Action potential moves along the nerve
Voltage gated calcium channels open allowing influx of calcium
Vesicles of acetyl choline released into synaptic cleft

Acetyl choline diffuses across the synaptic cleft
The acetylcholine receptor opens and renders the membrane permeable to Na / K ions
The depolarisation starts an action potential at the motor end plate

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7
Q

what does acetylcholinesterase do

A

converts acetyl choline in acetate and choline

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8
Q

what happens to choline

A

is sequestered back into presynaptic vesicles

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9
Q

what are the main presynaptic NMJ disorders

A

botulism
lambert eaton myasthenic syndrome
abnormality of calcium/ sodium/ magnesium

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10
Q

what causes botulism

A

clostridium botulinum (organism present in soil- food and wounds can become infected)

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11
Q

what does botulinum toxin do

A

cleaves presynaptic proteins involved in vesicle (acetylcholine) formation and blocks vesicle docking with the presynaptic membrane

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12
Q

what are the features of botulism

A

rapid onset weakness without sensory loss

overwhelming paralysis

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13
Q

what causes lambert eaton myasthenic syndrome (LEMS)

A

antibodies to presynaptic calcium channels leads to reduced vesicle release of ACh

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14
Q

what is LEMS strongly associated with

A

underlying small cell carcinoma

50% paraneoplastic syndrome, 50% autoimmune

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15
Q

what is the treatment for LEMS

A

3-4 diaminopyridine

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16
Q

what is the treatment for botulism

A

self limiting condition

supportive- ventilation

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17
Q

what is the main post synaptic MNJ disorder

A

myasthenia gravis

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18
Q

what causes myasthenia gravis

A

autoimmune disorder- antibodies against acetyl choline receptors
= reduced number of functioning receptors leads to muscle weakness and fatiguability
=flattening of end plate folds

even with normal amounts of ACh, transmission becomes insufficient when receptors drop by 30%

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19
Q

where do you get weakness in MG

A

strange presentations

  • around eyes (ptosis)
  • paraveterbal muscles
  • facial muscles (square smile, flat facial expression)
  • resp muscles (resp arrest)
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20
Q

what do the antibodies do in MG

A

block the binding of ACh and also trigger inflammatory response that damages the folds of postsynaptic membranes

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21
Q

what organ is particular involved in MG

A

thymus- 75% have hyperplasia/ thymoma

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22
Q

who gets MG

A

females in 3rd decade

males in 6/7th decade

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23
Q

what are the clinical features of MG

A

weakness typically fluctuating - worse at end of day
most commonly extraocular weakness, facial and bulbar weakness
limb weakness is typically proximal

(hard to keep eyes open watching TV,get tired eating meals)

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24
Q

what is the acute treatment for MG

A
  • acetylcholinesterase inhibitor - pyridostigmine (allows persistence of ACh in the synaptic cleft)
  • IV immunoglobulin

thymectomy (controversial)

25
Q

what is the long term treatment for MG

A

-acetylcholinesterase inhibitor - pyridostigmine (allows persistence of ACh in the synaptic cleft)
(immunomodulation)
-steroids (high doses of prednisolone)
then
-steroid sparing agents (azathioprine/ mycophenolate)

emergency treatment with plasma exchange or immunoglobulin

26
Q

what drug should you always avoid in MG

A

gentamicin - can cause MG crisis

27
Q

what is the prognosis for MG

A

3-4%

from resp failure and aspiration pneumonia/ immunosuppression in the elderly

28
Q

what is the smallest contractile unit in skeletal muscle

A

muscle fibre - sarcomere

29
Q

what is a sarcomere

A

from one z line to the next, is the basic functional unit of the muscle

30
Q

what are the features of LEMS

A

gradual onset of leg and arm weakness

31
Q

what surrounds each muscle fibre

A

endomysium

32
Q

what forms a fascicle

A

20-80 muscle fibres

33
Q

what wraps round a fascile

A

perimysium

34
Q

what wraps around skeletal msucle

A

epimysium (extends from tendon)

35
Q

what are the features of smooth muscles

A

not striated
single central nucleus
gap junction between cells
no sarcomeres

36
Q

what are the different types of muscle fibres

A

type 1- slow oxidative (dense capillary network, myoglobin, resist fatigue)
type IIa - fast oxidative (aerobic metabolism)
type IIb- fast glycolytic (easily fatigued)

37
Q

what are fasciculations

A

visible fast, fine, spontaneous twitch

38
Q

can fasciculations be normal

A

yes in healthy muscles (large) can be caused by stress, caffeine, fatigue

39
Q

when are fasciulations abnormal

A

occur in denervated muscle which becomes hyperexcitable - usually a sign of disease in the motor neurone not the muscle
(abnormal in small muscles)

40
Q

what is myotonia

A

failure of muscle relaxation after use

due to chloride channel disorder (usually hereditary)

41
Q

what are the symptoms/ signs of muscle disease

A

myalgia
muscle weakness
wasting
hyporeflexia

42
Q

what are the causes of neck weakness with drop

A

motor disease
muscle disorders
myositis
myopathy

43
Q

what are the immune mediated muscle diseases

A

dermatomyositis

polymyositis

44
Q

what are the inherited muscle diseases

A

muscular dystrophies
dystrophinopathies
limb girls muscular dystrophies
myogenic dystrophy

45
Q

what are the congenital muscles diseases

A

congential myasthenic syndromes

congenital myopathies

46
Q

what are the symptoms/ signs of polymyositis

A 
symmetrical, progressive proximal weakness developing over weeks to months
Raised CK (in 1000s)- responds to steroid
47
Q

what are the symptoms/ signs of dermatimyositis

A

clinically similar but associated with skin lesions ‘heliotrope rash’
50% have underlying malignancy

48
Q

what is inclusion body myositis

A

slowly progressive weakness in 6th decade of life with characteristic thumb sparing

49
Q

what is myotonic dystrophy

A

commonest muscular dystrophy

AD

50
Q

what are the features of myotonic dystrophy

A 
myotonia 
weakness
cataracts 
ptosis 
frontal balding 
cardiac defects
51
Q

what are the features of muscular dystrophies

A

inherited
noninflammatory
progressive
no central/ peripheral nerve abnormality

duchenne and becker most common

52
Q

what are the common infective muscle diseases

A

viral- coxsacchie
trypanosomiasis
cistercosis - uncooked pork
borrelia

53
Q

what are the toxic causes of muscle disease

A

drugs

venoms

54
Q

what are the congenital muscle diseases

A

congenital myasthenic syndromes

congenital myopathies

55
Q

what drugs cause myopathies

A

statins- myalgia, myopathy, persistent myositis
steroids
duiretics

56
Q

what is rhabdomyolosis

A

dissolution of muscle

damage to skeletal muscle causes leakage of large quantities of toxic intracellular contents into plasma

57
Q

what can cause rhabdomyolsis

A

crush injuries
toxins
post convulsions
extreme exercise

58
Q

what are the features of rhabdomyolsis

A

myalgia
muscle weakness
myoglobinuria
complications = acute renal failure and DIC

59
Q

what are the MRC muscle power grades

A

0 – no movement at all
1 - flicker of movement when attempting to contract muscle
2 – some muscle movement if gravity removed but none against gravity
3 - movement against gravity but not against resistance
4 – movement against resistance but not full strength
4- not alright but they are managing
4+ almost normal but not quite
5 – normal strength

Neurology (35 decks)

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