What's the definition of Myasthenia Gravis?

Progressive autoimmune disorder of the nervous system causing sporadic weakness of the voluntary and skeletal muscles, generally the face , lips, tongue, neck and throat.

What is the etiology of Myasthenia Gravis?**

T cell and various antibodies attacking and impairing or destroying nicotinic acetylcholine receptors athe the motor end-plate. **

Tumor of the thymus gland in 10% of patients.

Prevalence has risen from the 1950's

What is the pathophysiology of Myasthenia Gravis?

Patient produces antibodies against acetylcholine which destroys the receptors via the Tcell mediated immunity.

What is the history of Myasthenia Gravis?

-Family history in 10-20% of patients

- Voluntary muscle weakness exacerbated by continuous use, increased fatigue, dysphagia, diplopia, fluid regurgitaion through nose when drinking, progressive hypophonia (soft speech)

What is the presentation of a patient with Myasthenia Gravis?

-Emaciated due to difficulty eating

-Poor skin turgor due to decreased fluid intake & dehydration

-Diminished visual acuity, visual field deficits, ptosis, strabismus

       -Ocular muscles usually 1st to be affected

       - 80% have diplopia and ptosis

-Excessive salivation due to inablilty to swallow, diminished tongue strength

 - Next muscles to be affected are innervated by the cranial nerves & down -facial, neck, upper ext, lower ext.

What are the differential diagnosis of Myasthenia Gravis?

Botulism (botox)

Amyotrophic lateral sclerosis (ALS)

Ophthalmoplegia

Eaton-lambert syndrome

brain lesion

Muscular Dystrophy

What are the diagnostic tests for Myasthenia Gravis?

*Electromyography (EMG)          *need for diagnosis

*AchR antibodies - 85% of patients

*Tensilon test - within 30 seconds of administration of Acetylcholinesterase incubators, muscle strength occurs

Ice test - ptosis improves after application of ice near eyelid for 2 min.

What is the treatment for Myasthenia Gravis?

Neurology referal

Mestinon (acetlycholinesterase inhibitor)

Thymectomy if warrented

Immunosuppression - prednisone

                               - cyclosporin

                              - imuran (may take 12 months to peak, then taper after 12-24 months then d/c

IV IgG and plasma exchange - transient improvement

What is involved in the physical exam of a patient with Myasthenia Gravis?

Ptosis - improves with rest

Ask patient to lift head off pillow when supine 

hold arms above head while sitting

Deep tendon reflexes and sensory - normal

Myasthenic Crisis

Appears from no apparent cause. Symptoms more sever with swollowing and respiratory difficulties.

Tensilon for muscle strenth

Ventilator support for respiratory failure

Plasma phoresis or IV IgG

Temporarily stop Cholinesterase inhibitors and resume in 2-3 days