Myasthenia Gravis is a disease of the neuromuscular junction, presenting symptoms like weakness and fatigue.

Etiology: autoimmune process by acetylcholine-receptor antibodies leads to a decreased number of active and functional acetylcholine receptors at the postsynaptic membrane.

Presentation: fatigue, diplopia, ptosis and difficulty swallowing. *muscle weakness.
Speech: mushy or nasal quality with facial weakness manifesting as a "snarling" appearance when smiling. Eventually the weakness becomes generalized, involving the proximal muscles in an asymmetric pattern.
Deep tendon reflexes are intact.

Eaton Lambert Myasthenic syndrome:
increasing muscle strength on repetitive contraction. ( normally associates with small cell carcinoma of the lung)

Botulism can mimic myasthenia, but the pupiles are usually dilated and repetitive nerve stimulation shows an incremental increase in muscular fiber contraction (opposite of myasthenia gravis)

Diagnosis: acetylcholine-receptor antibody test.
edrophonium (Tensilon) sensitive but no specific for the Dx. *side effects : nausea, diarrhea, bradycardia during test.
MOST ACCURATE TEST: EMG electromyography.
Finding: decremental decrease in muscle fiber contraction on repetitive nerve stimulation. (opposite to botulism as mentioned)

Treatment:
Anticholinesterase (pyridostigmine) symptomatic treatment for MG.
Glucocorticoids: effective for improving weakness (takes long 1-3 months)
Azathioprine: use in combination with steroids. (3-6 months)
Cyclosporine A and occasionally methotrexate and cyclophosphamide are used for severe cases
Plasmapheresis and IV immunoglobuline. mostly for acute crisis.
Thymectomy: INDICATED in post pubertal patients and less than 55 yrs.

The Myasthenia Gravis Foundation of America Clinical Classification divides MG into 5 main classes and several subclasses[3] :

Class I: Any ocular muscle weakness; may have weakness of eye closure; all other muscle strength is normal
Class II: Mild weakness affecting other than ocular muscles; may also have ocular muscle weakness of any severity

Class IIa: Predominantly affecting limb, axial muscles, or both; may also have lesser involvement of oropharyngeal muscles

Class IIb: Predominantly affecting oropharyngeal, respiratory muscles, or both; may also have lesser or equal involvement of limb, axial muscles, or both
Class III: Moderate weakness affecting other than ocular muscles; may also have ocular muscle weakness of any severity

Class IIIa: Predominantly affecting limb, axial muscles, or both; may also have lesser involvement of oropharyngeal muscles

Class IIIb: Predominantly affecting oropharyngeal, respiratory muscles, or both; may also have lesser or equal involvement of limb, axial muscles, or both
Class IV: Severe weakness affecting other than ocular muscles; may also have ocular muscle weakness of any severity

Class IVa: Predominantly affecting limb, axial muscles, or both; may also have lesser involvement of oropharyngeal muscles

Class IVb: Predominantly affecting oropharyngeal, respiratory muscles, or both; may also have lesser or equal involvement of limb, axial muscles, or both; use of a feeding tube without intubation
Class V: Defined by the need for intubation, with or without mechanical ventilation, except when used during routine postoperative management

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