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Questions about Myasthenia Gravis (MG)

Exam questions about Myasthenia Gravis (MG) for doctors clinical exams, medical student finals, OSCES, PACES and USMLE


Question 1

How do you demonstrate fatigueability in a neurological examination?

  • Click here for the full answer to this question
  • In summary:
    • Ocular myasthenia
      • Sustained upgaze and repeated blinking
    • Limb weakness
      • Ask the patient to lift their arms to 90 degrees and check their shoulder abduction and adduction. If this is equal, then ask them to move ONE ARM up and down 20 times
      • Then retest shoulder abduction and adduction and compare sides
    • Central/bulbar involvement
      • Test the power of head/neck flexion and extension (fatigue this movement as above)
      • Ask the patient to take a deep breath and count out loud as many numbers as they can

Question 2

What are the two groups of patients who tend to be diagnosed with myasthenia gravis?

  • Young women (20-35)
    • Tend to present with a generalised, and often acute condition
  • Older men (60-75)
    • Who tend to present with prominent oculobulbar involvement

Question 3

What are the classical presentations of myasthenia gravis?

  • Patients usually present with fatigueable weakness
    • Progressively weakness over the course of the day is classic. The weakness improves with rest
  • Ocular and bulbar involvement is also possible, leading to ptosis, swallowing difficulties and speech disturbance

Question 4

What are the main differential diagnoses of myasthenia gravis?

The differential diagnosis of MG depends on the type of presentation:

  • Acutely (rapidly progressive or sudden weakness)
    • Infection
      • Botulism
      • Lyme disease
    • Inflammatory
      • Guillain-Barré Syndrome (GBS) and variants
    • Vascular
      • Brainstem or spinal cord infarct
  • Ptosis or eye movement disorder
    • Bilateral Horners syndrome or third nerve palsy (check pupil for involvement)
    • Thyroid eye disease
    • Sarcoid
    • Lyme disease
    • Mitochondrial disease
  • Oculo-bulbar weakness
    • Pseudobulbar palsy (c0rticobulbar tract lesion)
    • Osmotic demyelination
    • Space occupying lesion
    • Vascular (stroke)
    • Motor neurone disease (look for fasciculations, especially of the tongue)
    •  Infection
      • Botulism
      • Lyme disease
    •  Parainfectious/Inflammatory
      • Guillain-Barré Syndrome and variants

Question 4

What antibodies are present in myasthenia gravis?

  • Anti-AChR antibodies are present in approximately 90 percent of patients with classical myasthenia, but can be as low in as 50-70 percent in ocular disease
    • False positive AChR Abs can occur in LEMS (approximately 5%) and Motor Neuron Disease (3-5% percent)
  • Anti-MUSK antibodies
    • Antibodies to the Muscle Specific Kinase (MuSK) are present in 40-50 percent of those with generalized myasthenia gravis who are AChR-Ab negative
  • Anti-striated muscle antibodies, and anti-thyroid antibodies can also be present but may not be specific
  • Approximately 10% of patients are ‘seronegative’ (negative AChR and MUSK antibodies)

Question 5

What is the most important initial investigation in suspected myasthenia gravis?

  • Forced vital capacity (FVC) is the key initial investigation in first presentation or flare
  • If this is low (<1.5l) then make sure ITU are at least aware of the patient, as they can rapidly deteriorate and require intubation and ventilation
  • Measure this at least 4-hourly in patients with acute/relapsed MG at presentation

Question 6

What treatments are used for the underlying issues in myasthenia?

  • Immunosuppression is the main stay of treatment
  • Acutely (and in flares)
    • IVIG and/or plasma exchange
      • If plasma exchange is available, always exchange BEFORE giving IVIG (or you will just exchange all the IVIG out of circulation)
    • Steroids (e.g. methylprednisolone or prednisolone)
      • NB. Steroids may lead to a transient and sometimes significant worsening of MG and should therefore be uptitrated gradually and patients monitored closely
  • Longer term
    • Steroids (e.g. prednisolone)
      • NB. Steroids may lead to a transient and sometimes significant worsening of MG and should therefore be uptitrated gradually and patients monitored closely
    • Steroid sparing agents are used, usually azathioprine
      • TPMT levels should be checked as those with low levels are at risk of sensitivity to azathioprine
  • Thymectomy
    • Thymectomy can cause improvement and even remission in up to 80% of MG, especially the young population, and is usually recommended


Click here for full information on the diagnosis and management of myasthenia gravis

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