Exam Cram

• Myasthenia Gravis is caused by auto-antibodies that attack the acetylcholine receptors on the neuromuscular junction

• Presentation: fatigable muscle- diplopia, ptosis, truncal muscle weakness, worst at the end of the day

• Investigation: Anti acetylcholine antibodies

• Management: Pyridostigmine

Outline

Background 

• Myasthenia Gravis- 10,000 patients in UK (1/10,000)

• Associated with thymoma

Assessment

Presentation

• Myasthenia Crisis

• Eye clinic- diplopia

• TIA referral- dysphagia, limb weakness

• Variable musle weakness

Examination:

• Voice tires counting to 100

• Ptosis

• Diploplia, ophhthalmogplegia

• Specific group weakness-triceps, normal sensation & reflexes

Investigations Sensitivity Specificity

• Anti ACh 85% 99%

• Anti MUSK 10% 99%

• CXR widened mediastinum: 10% have thymoma

• CT-Thorax: thymoma

Diagnosis

Diagnostic criteria: positive anti-ACh or MUSK

Differentials: Lamberton- Eaton Syndrome, Motor Neuron Disease,  cranial neuropathy

Management

Acute (Myasthenic Crisis)

• Steroids

• IV Ig > Plasma exchange

• New diagnosis work up: CT-Thorax ?thymoma

• Disposition: admission

Long Term

Goals of care: prevent acute crisis & global deterioration

1. Pyridostigmine

2. Steroids

3. DMARDS- azathioprine, MMF, 

Bulbar Myasthenia Gravis

• Type of Myasthenia gravis where bulbar cranial nerves are affected. 

• Presents with partial ptosis, diplopia, nasal regurgitations and weak cough. 

• Diagnosis & management as per Myasthenia Gravis. 

Myasthenia Crisis

Presentation: severe exacerbation resulting in acute muscle weakness, of concern respiratory and diaphragm muscles for breathing. 

Causes of crisis

1. Respiratory infections

2. Surgery

3. Pregnancy

4. Perimenstrual state

5. Medication

   • Betablockers

   • Antibiotics- aminoglycosides, fluoruquinolones & azithromycin

   • Anaesthetics

References and Resources

1. https://www.nhs.uk/conditions/myasthenia-gravis/#:~:text=Many%20people%20with%20myasthenia%20gravis,the%20thymus%20called%20a%20thymoma.

Page written in 2024.