Neuro Flashcards
What 2 antibodies are associated with myasthenia gravis
- Anti-Ach receptors antibodies
- Anti-Muscle-specific tyroine kinase antibodies (Anti-MuSK)
- LDL receptor-related protein 4 (Anti-LRP4)
What is myasthenia gravis
Chronic autoimmune disorder of the postsynaptic membrane at the neuromuscular junction of skeletal muscle
Describe the gender differences in myasthenia gravis
- Men typically affected over 60
- Women affected under 40 (mc)
Describe the association between the thymus and myasthenia gravis
- 10% patients have a thymoma
- 70% have thymic hyperplasia
Explain how Anti-AchR causes the symptoms of myasthenia gravis
- antibodies against Ach receptors competitively inhibit Ach binding = weakness
- Anti-AchR also activate the complement system within the NMJ which leads to damage to cells at the postsynaptic membrane
Explain why increased muscle activity causes worse symptoms in people with myasthenia gravis
- Receptors are used more during muscle activity so more become blocked up
- Leads to less effective stimulation of the muscle with increased activity
Give 6 clinical manifestations of myasthenia gravis
- Ptosis and diplopia (early)
- Muscle strength fatigability - weakness worsens with activity or repetition and improves on rest
- Dysarthria (speech) and dysphagia (chewing/ swallowing)
- Facial paresis - transverse smile
- Proximal limb weakness - e.g. hard to climb stairs
How are tendon reflexes and sensations affected in myasthenia gravis
They remain intact/ normal
How is myasthenia gravis investigated
- Serology - Anti AchR and MuSK
- Repetitive nerve stimulation - shows a decremental muscle response
- Single fibre electromyography (sensitive)
- CT chest - thymus enlargement
How is myasthenia gravis managed
- 1st - long acting Acetylcholinesterase inhibitor e.g. pyridostigmine
- 2nd - Prednisolone
- 3rd - Immunosuppressant e.g. Azathioprine
- Thymectomy if thymoma is present
Name 3 drugs that may exacerbate myasthenia gravis
- beta blockers
- lithium
- phenytoin
- antibiotics: macrolides, tetracyclines
What is myasthenic crisis
Medical emergency where respiratory muscles weaken and is often provoked by infection or medications
Give 4 ways myasthenic crisis may present
- Increasing shortness of breath
- Severe limb weakness
- Quiet breathing
- Reduced chest expansion
How is myasthenic crisis managed
- Intubation and mechanical ventilation
- Plasma exchange or IV Ig
What is Lambert-Eaton myasthenic syndrome
Rare autoimmune condition affecting both NMJ and autonomic ganglia
Which type of cancer is Lambert-Eaton syndrome associated with
Small cell lung cancer
Explain the pathophysiology of Lambert-Eaton syndrome
- Antibodies are produced against voltage gated Ca2+ channels in presynaptic membrane
- This means there is insufficient Ca to trigger release of Ach into the neuromuscular junction = reduced Ach
Give 6 clinical manifestation of Lambert-Eaton syndrome
- limb-girdle weakness (affects lower limbs first) - waddling gait
- Strength improved with repeated exertion
- Dry mouth (Xerostomia)
- Ptosis and diplopia (late Sx)
- Dysarthria (difficulty speaking due to weak muscles)
How are tendon reflexes affected in Lambert-Eaton syndrome
Reduced/ absent in most patients