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neuromuscular disorders Flashcards

1
Q

signs/symptoms of muscle disease

A
  • Myalgia
  • Muscle weakness – often specific patterns of weakness depending on cause – proximal etc
  • Wasting
  • Hyporeflexia
  • Myotonia
    o Failure of muscle relaxation after use
    o Chloride channel
  • Fasciculations
    o Can be normal – stress, caffeine, fatigue
    o Occur in denervated muscle which becomes hyperexcitable
    o Usually a sign of disease in motor neuron – not muscle
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2
Q

presynaptic + postsynaptic neuromuscular disorders

A

presynaptic
- botulism - clostridium botulinum
- lambert eaton syndrome

postsynaptic
- myasthenia gravis

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3
Q

clostridium botulinum

A

gram positive anaerobic bacillus
produces botulinum toxin
- a neurotoxin which irreversibly blocks the release of acetylcholine
–> often affects bulbar muscles + ANS

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4
Q

pathophysio of clostridium botulin

A

botulin toxins cleaves preynaptic protein involved in vesile formation + blocks vesicle docking with presynaptic membrane

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5
Q

causes of clostridium botulinum

A

organism found in soil
from eating contaminated food (tinned)

IV drug use - black tar heroin

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6
Q

features + treatment of clostridium botulinum

A

patient fully conscious with no sensory disturbance
flaccid paralysis
diplopia
ataxia
bulbar palsy

Mx = botulism antitoxin + supportive care - only effective if given early

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7
Q

lamber eaton myasthenic syndrome

A

progressive muscle weakness, improves with increased use as a result of damage to neuromuscular junction

assoc with small cell carcinoma - antibodies produced by immune system against voltage gate calcium channles in small cell lung cancer

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8
Q

pathophysio of lambert eaton

A

antibodies target + damage the voltage gated calcium channels in PREsynaptic terminals of the neuromuscular junction where motor nerves communicate with muscle cells

 These voltage-gated calcium channels are responsible for assisting in the release of acetylcholine into the synapse of the neuromuscular junction
 This acetylcholine then binds to acetylcholine receptors + stimulates a muscle contraction

 When these channels are destroyed, less acetylcholine is released into the synapse

(antibodies to presynaptic calcium channels leads to less acetycholine vesicle release)

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9
Q

presentation of lambert eaton syndrome

A

symptoms develop slowly
proximal muscles - proximal leg weakness
diplopia - intraoculare muscles
ptosis - levator muscles
dysphagia - oropharyngeal muscles

autonomic dysfunction - dry mouth, blurred vision, impotence

reduced tendon reflexes - reflexes become temporarily normal after a period of strong muscl contraction = post-tetanic potentiation

worsens with increased temperature

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10
Q

treatment of lambert eaton syndrome

A

3,4 diaminopyridine (amifampridine)
- allows more acetylcholine to be released at junction
- blocks voltage gated potassium channels in presynaptic cells

check for underlying small cell lung cancer

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11
Q

myasthenia gravis

A

autoimmune condition that causes muscle weakness that gets progressively wore with activity + improves with rest

bimodal peaks - women (30s), men (60-70s)
assoc with thymic hyperplasia/thymoma

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12
Q

myasthenia gravis pathophysio

A

Acetylcholine receptor antibodies are produced by the immune system
o These bind to post synaptic neuromuscular junction receptors blocking stiumulation to trigger muscle contractions

As the recptors are used more during activity, more of them become blocked up
o This leads to less effective stimulation of the muscle with increased activity
o This improves with rest as more receptors are freed up again

These antibodies also activte the complement system triggering inflammatory cascade within the neuromuscular junction
o Leading to damge to cells at postsynaptic membrane – worsens symptoms

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13
Q

myasthenia gravis presentation

A

weakness that gets worse with muscle use + improves with rest
- worse at end of day

proximal muscles
- diplopia, ptosis, dysphagia
- weak facial movements - chewing
- slurred speech
- progressive weakness with repetitive movements

thymectomy scar

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14
Q

myasthenia gravis examination

A

repeated blinking -> exacerbates ptosis

prolonged upwards gaze - exacerbates diplopia on further movements

abduct one arm 20 times - then compare both sides

test forced vital capacity(FVC) - reduced

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15
Q

myasthenia gravis investigation

A

testing for antibodies
- acetylcholine receptor (Ach-R) antibodies
- muscle-specific kinae (MuSK)
- LRP4

single fibre EMG

CT or MRI of thymus - thymoma

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16
Q

management of myasthenia gravis

A

pyridostigimine (acetylcholinesterase inhibitor)
- increases amount of acetylcholine in the neuromuscular junction + improves symptoms

immunosuppression - prednisolone, azathioprine
- suppress the production of antibodies

thymectomy

17
Q

which antibiotic should be avoid in myasthenia gravis?

A

gentamicin

18
Q

emergency treatment for myasthenia gravis

A

plasma exchange or immunoglobulin

19
Q

polymyositis + dermatomyositis

A

autoimmune condition where inflammation is in the muscle

polymyositis = condition of chronic inflammation of muscles
dermatomyositis = connective tissue disorder where there’s chronic inflammation of skin + muscle

can be caused by underlying malignancy (making them paraneoplastic syndromes

20
Q

Polymyositis + dermatomyositis presentation

A

muscle pain, fatigue, WEAKNESS - worsens over months
occurs bilaterally + typically affects proximal muscles

mostly affects shoulder + pelvic girdle
develops over weeks

other organ involvement
- interstitial lung disease + resp muscle weakness
- dysphagia
- myocarditis
- fever, weight loss, raynauds

21
Q

dermatomyositis skin features

A
  • Gottron lesions – scaly erythematous patches on knuckles, elbows + knees
  • Photosensitive erythematous rash – on back, shoulders, neck
  • Purple rash on face + eyelids (helitope rash)
  • Periorbital oedema – swelling around eyes
  • Subcutaneous calcinosis – calcium deposits in subcutaneous tissue
22
Q

Polymyositis + dermatomyositis investigations

A

definitive diagnosis = muscle biopsy

creatine kinase = GOLD
- usually over 1000 (normal - 300ish)

autoantibodies
- anti-jo
- anti-Mi-2
- anti-nuclear

electromyography (EMG) - increased fibrillation, abnormal motor potentials, repetitive discharges

23
Q

Polymyositis + dermatomyositis management

A

rheum, physio, occupational
new cases assess for cancer

steroids = 1st line

if inadequate
- immunosuppressants - azathioprine
- IV immunoglobulins

biological therapy - infliximab

24
Q

muscular dystrophy + a key sign of it

A

group of genetic conditions that cause gradual weakening + wasting of muscles

gower’s sign
- Proximal muscle weakness of pelvic girdle
- Use hands on legs to helps them stand up

25
Q

myotonic dystrophy mode of inheritance

A

commonest muscular dystrophy
autosomal dominant
presents in adulthood - 20s

trinucleotide disorder with anticipation

26
Q

myotinic dystrophy presentation

A

prolonged muscle weakness
prolonged muscle contractions (myotonia) - patient unable to let go after shaking someones hand, let go of door knob

dysarthria, wasted SCM
cataracts
cardiac arrhythmias, testicular atrophy
bilateral ptosis, frontal balding

27
Q

duchennes muscular dystrophy

A

x linked recessive
- affected mother has 50% chance of giving to kids
- dystrophin deficiency/absence - dystrophin is protein that helps hold muscles together

life expectancy 25-35yrs
usually dead by 20 due to cardio/resp problems

28
Q

difference in pathophysio between beckers and duchennes muscular dystrophy

A

in beckers dystrophy, dystrophin is present but levels are low - progresses much more slowly

beckers also presents older (8-12) and live longer ish

29
Q

duchennes presentation

A
  • Boys aged 1-6 – onset 3-4yrs
  • Developmental delay
  • Proximal muscle waster
  • Toe walking
  • Exaggerated lumbar lordosis
  • Pseudohypertrophy of calves
  • Gowers manoeuvre
  • Dystrophin also present in brain – some boys present with learning difficulties/cognitive problems
30
Q

complication of duchennes

A

dilated cardiomyopathy

31
Q

management of duchennes

A

no cure
steriods may delay progression
creatine supplementation

MDT, resp support

32
Q

spinomuscular atrophy type 1

A
  • Autosomal recessive
  • Abnormal messenger RNA – doesn’t get transcribed
  • Can get corrected by RNA therapy maybe
  • Progress loss of anterior horn cells in spinal cord + brain
  • Autosomal recessive
    o SMN1 deficiency, on chromosome 5
  • Proximal muscle weakness
  • Hypotonia
  • Tongue fasciculation
33
Q

prader-willi

A
  • Chromosome 15
  • floppy baby
  • Neonate = weak muscles, poor feeding, slow development
  • Child = constantly hungry, obesity, T2DM
  • Hypogonadism, learning difficulties

mx - Orlistat

34
Q

rhabdomyolysis pathophysio

A

Muscle cells (myocytes) undergo cell death apoptosis)
Cell death results in muscle cells releasing –
o Myoglobin – causing myoglobinuria
o Potassium
 Hyperkalaemia -> arrhythmias -> cardiac arrest
o Phosphate
o Creatine kinase

Breakdown products are filtered by the kidney + cause injury to kidney
o Myoglobin is toxic to kidney in high conc
o Results in AKI -> causes further accumulation of breakdown products in blood

35
Q

rhabdo investigations

A

Creatine kinase (CK)
o Will be in thousands-hundreds of thousands
o Higher CK increases risk of kidney injury

Myoglobinuria = myoglobin in urine
o Gives red-brown colour
o Causes urine dipstick to be positive for blood

U&Es – AKI, hyperkalaemia

ECG – hearts response to hyperkalaemia (tall tented Twaves)

36
Q

rhabdo causes

A

seizure
collapse/coma (e.g. elderly patients collapses at home, found 8 hours later)
ecstasy
crush injury
McArdle’s syndrome
drugs: statins (especially if co-prescribed with clarithromycin)

37
Q

rhabdo mx

A

IV fluids

(IV sodium bicarb, IV mannitol (increase GFR))

neuro (26 decks)

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