myasthenia gravis

Question 1

symptoms of MG

Answer 1

• extraocular muscles
• – ptosis
• pupils unaffected
  — diplopia
  Typically at the end of the day
• ophthalmoplegia

BULBAR involvement - dysphagia, dysphonia, dysarthria, weak face and jaw

limb weakness
- proximal and symmetrical

neck weakness - neck flexion and extension

resp muscle weakness -SOB

distended neck veins and flushed face are likely to be caused by superior vena cava obstruction, which can be a complication of thymomas. Thymomas are associated with myasthenia gravis

Question 2

complications of MG

Answer 2

resp failure

myasthenic crisis -
when the muscles that control breathing weaken to the point where individuals require a ventilator to help them breathe. It may be triggered by infection, stress, surgery, or an adverse reaction to medication.

drooling, weak neck, slack facial muscles

Question 3

Ix for MG

Answer 3

1. autoantibodies - AchR, MuSK, LRP4
2. single fibre electromyography EMG : high sensitivity (92-100%)
   - decrement in amplitude
   - increased jitter using a single-fibre electrode
3. CT thorax to exclude THYMOMA
   CK normal
4. tensilon test - IV edrophonium reduces muscle weakness temporarily - not commonly used any more due to the risk of cardiac arrhythmia

bloods - TFTs

spirometry - check vital capacity if below 1.5 litres requires transfer of the patient to ITU/HDU

Question 4

what is myasthenic crisis

Answer 4

• respiratory failure os the most common presentation
• resp muscle weakness, inability to clear bronchial secretions and bronchospasm all contribute to respiratory failure
• pregnancy may precipitate a myasthenic crisis

Slack facial muscles 
Weak neck
Drooling
Nasal speech
Generally weak 
Unsafe swallow

Question 5

cholinergic crisis?

Answer 5

Looks similar to myasthenic crisis.
Excess of acetylcholinesterase inhibitors
excessive stimulation of striated muscle - flaccid paralysis
Respiratory failure
Miosis and the SLUDGE syndrome
(ie, salivation, sweating, lacrimation, urinary incontinence, diarrhea, GI upset and hypermotility, emesis) also may mark cholinergic crisis-not inevitably present

Question 6

what is tensilon test

Answer 6

allows MG patient to move muscles normally

Question 7

tensilon test CI when

Answer 7

Caution – asthma, MI, bradycardia

Cardiac monitoring

Question 8

early management of MG

Answer 8

Supportive measures
Bedside spirometry
FVC
If falling rapidly or FVC< 20ml/kg review as may need ventilation
Blood gases ↑CO2 ↓O2 acidosis late manifestations of type II respiratory failure

Question 9

therapeutic management fo MG

Answer 9

Anticholinesterase inhibitors-
- Pyridostigmine
Onset 30min; peak 60-120min; duration 3-6hr
- Neostigmine (ITU)

• Corticosteroids
  Start low – high dose may paradoxically worsen symptoms
• Azathioprine - Steroid sparing
• IV immunoglobulin
  Acute decline or crisis – 60% will respond after 7-10 days
  Plasmapheresis- removes AChR antibodies ->short-term improvement
  Similar efficacy to IV Ig

Question 10

what findings are elicited or seen in a MG patient during an examination

Answer 10

• Repeated blinking will exacerbate ptosis
• Prolonged upward gazing will exacerbate diplopia on further eye movement testing
• Repeated abduction of one arm 20 times will result in unilateral weakness when comparing both sides
• thymectomy scar
• test for forced vital capacity

when checking the eye ask them to count fingers

ask initially if they have double vision

if yes then ask if it gets worse with any movement

if no ask if they do get any DV at any point

swallowing

does anyone not understand them

chicken arms

Question 11

Risk factors of a MG patient

Answer 11

DVT

swallowing test so NBM until then if necessary do feeding tube

Resp test FVC if that is not possible then do single breath test

Question 12

Mx of myasthenic crisis

Answer 12

non-invasive ventilation with BiPAP or full intubation and ventilation.

plasmapheresis
IVIG

Question 13

what is lamber eaton syndrome
Sx
Ix
Mx

Answer 13

antibodeis attacking NMJ

weakness of the proximal limb muscles esp lower limbs

no ocular and other cranial nerves involvement

gets better after exercise

Ix EMG

ass w small cell carcinoma

Mx
guanethidine hydrochloride
4-aminopyridine
IVIG and plasmapharesis

Question 14

where is botulim toxin used clinically

Answer 14

cervical dystonia
blepharospasm
sever limb spasticity following stroke or MS

Question 15

associations of MG

Answer 15

• thymomas in 15%
• autoimmune disorders: pernicious anaemia, autoimmune thyroid disorders, rheumatoid, SLE
• thymic hyperplasia in 50-70%

Question 16

causes of myasthenic crisis

Answer 16

• emotion
• exercise
• hypokalaemia - certain drugs e.g. opiates, some antibiotics tetracycline and β-blockers
• intercurrent infection
• sudden medication discontinuation.

Question 17

what is myasthenia gravis

Answer 17

autoimmune disorder characterised by the presence of acetylcholine receptor antibodies and depletion of acetylcholine receptors.