Myasthenia gravis is an autoimmune neurological disorder caused by autoantibodies against the acetylcholine receptor or against a receptor-associated protein, muscle-specific tyrosine kinase (MuSK-Ab).
The autoimmune attack at the muscle endplate leads to failure of neuromuscular transmission and eventually muscle weakness.
In the active phase of the disease, symptoms typically fluctuates and then become severe; myasthenic crisis occur in this phase.
In the stable/inactive phase, symptoms are stable but still persist; it usually worsen attributable to infection, fatigue, tapering of medications or other identifiable factors.
In the burnt-out phase, remission may occur wherein patients are on immunotherapy and symptom-free, or may even be off medications.
In 15-20 years, if the symptoms left untreated, patient's weakness becomes fixed wherein the most severely affected muscles become atrophic.
Myasthenia gravis is an uncommon neurological disorder caused by autoantibodies against the acetylcholine receptor, against a receptor-associated protein, muscle-specific tyrosine kinase (MuSK-Ab), or occasionally to the low-density lipoprotein receptor-related protein 4 (LPR4)
The autoimmune attack at the muscle endplate leads to failure of neuromuscular transmission & eventually muscle weakness
Signs and Symptoms
Fatigability & weakness of voluntary muscles
Weakness tends to increase during repeated use
May improve with rest or sleep
Diplopia & ptosis
Common initial complaints
Cogan’s lid twitch or excessive lid elevation
Facial weakness which results in snarl-like expression when smiling
Nasal or slurred speech
Difficulty in swallowing
If generalized, there will be weakness in the limb muscles
Often asymmetric & proximal
Deep tendon reflexes & sensation are preserved
If severe, there will be shortness of breath
Acetylcholine Receptor Myasthenia Gravis
Muscle weakness predominant in the limb than bulbar, neck extensor than neck flexor, prominent ptosis & external ocular muscle weakness
Wasting of proximal limb & ocular muscles in long-standing disease (myasthenic myopathy)
Thymus pathology: 65% hyperplasia, 15% thymoma
Risk of recurrent crisis is low
Muscle-Specific Tyrosine Kinase Myasthenia Gravis
Muscle weakness predominant in the bulbar than the limb, neck flexor than neck extensor, mild ptosis & external ocular muscle weakness
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