1. Myasthenia gravis Mys + a + sthenos = muscle without strength
Urbir Sidhu
MD 4

2. What is it?
Myasthenia gravis is an autoimmune disease where antibodies are formed to acetylcholine receptors on motor end plates of skeletal muscle (neuromuscular junction)
Ach is produced in normal amounts, but these antibodies prevent binding of Ach to its receptor on the motor end plate
Due to this, End plate potential & Action potential cannot be generated, resulting in muscular weakness

3. What do you see?
Severe muscle weakness especially of arms, legs, & eyes
Muscle weakness is generalized but usually fluctuation and becoming more pronounced towards the end of the day
Weakness most prominently affects extraocular eyes
Electromyography shows progressively weaker contraction of muscles on repeated stimulation
Muscle histology appears normal

4. Epidemology More commonly seen in women Affects 3 in 100,000 people
Two age peaks: years (women) and years (men)
Thymic hyperplasia (65%) and thymoma (15%) found among younger patients

5. Pathogenesis
Cross-linking 2 adjacent AChRs with anti-AChR antibody, thus accelerating internalization and degradation of AChR molecules
Causing complement-mediated destruction of junctional folds of the postsynaptic membrane
Blocking the binding of ACh to AChR
Decreasing the number of AChRs at the NMJ by damaging the junctional folds on the postsynaptic membrane, thereby reducing the surface area available for insertion of newly synthesized AChRs

7. Clinical features
Muscle weakness that worsens with use and improves with rest
Predominantly involves facial muscles
Ptosis
Diplopia
Decresed facial expressions
Dysphagia
Dysarthria
Daily routines are tiring

8. Ptosis

9. Treatment Treatment is physiological based
Symptoms improve with use of anticholinesterase agents such as Neostigmine and Pyridostigmine
Drugs inhibit Acetyl cholinesterase
Acetylcholine remain in the synaptic cleft for longer period and in larger amounts, prolonging the time available for Ach to activate its receptors
Enables a larger amplitude of EPP (end plate potential) which will be able to generate muscle AP (action potential)
Better muscle contractions
Associated with thymic hyperplasia or thymoma
Thymectomy improves symptoms
The tensilon (edrophonium) test provides immediate improvement because this drug inhibits acetylcholinesterase.
Antibodies to acetylcholine receptor present in the serum of 80% of patients.

10. Myasthenia gravis
Before treatment
After 3 days of intravenous…

11. Differential: Lambert-Eaton Syndrome
Clinical condition resembles myasthenia gravis
But it is characterized by skeletal muscle weakness
May be associated with small cell carcinoma of lungs or any other autoimmune disorder