Myasthenia Gravis Overview



Myasthenia Gravis is an autoimmune disorder of the postsynaptic neuromuscular junction.  Ab to AChR blocks receptor function, resulting in diminished muscle contraction.  Associated with:

 - Thymic tumors

 - Paraneoplastic effects of SCC or Hodgkin lymphoma

 - Autoimmune: thyroid, Sjogren syndrome, rheumatoid arthritis, SLE



Myasthenia Epidemiology:

- Bimodal age distribution in the 30s (female predominance) and 60s-70s (male predominance).



Clinical Picture of Myasthenia Gravis:

- Fatiguability: Worse towards the end of the day

- Fluctuating degree/variable degree of weakness in:

	1. Ocular- 50%: Ptosis, diplopia

	2. Bulbar- 15%: Dysphagia, dysarthria, hypophonia, fatiguable chewing, loss of smile

	3. Neck: “dropping head syndrome”

	4. Limb- proximal weakness, arms > legs

	5. Respiratory muscles: “myasthenic crises”. Respiratory insufficiency and life-threatening



Differential DX:

- Thyroid ophthalmopathy

- Kearns-Sayre syndrome

- Myotonic dystrophy

- Brain stem/Cranial nerve pathology

- Generalized fatigue

- ALS

- Lambert Eaton myasthenia syndrome

- Miller Fischer and PCB variants of GBS

- Botulism

- Penicillamine induced myasthenia



Diagnosis - Clinical, Serologic and EMG Findings:

1. Clinical DX:

	- Bedside: ice pack test/Edrophonium test

	- Cogan sign

	- Peek sign

2. Imaging - CT Chest: Evaluate for thymoma

3. Electrophysiologic Confirmation:

	- Repetitive nerve stimulation

	- Single fiber electromyography

4. Labs:

	- AchR antibodies: first step in immunologic assay

	- MuSK antibodies

	- LRP4 antibodies



Myasthenia Gravis Treatment:

- Symptomatic Treatment: acetylcholinesterase inhibition

- Chronic Immunosuppressive Therapies: Steroids and NSAIDs

- Immunomodulating Treatments: IVIG and Therapeutic plasma exchange

- Surgical Treatment: Thymectomy



Myasthenia Crises - Severe bulbar weakness:

 - Dysphagia and aspiration and acute respiratory failure

 - Can be precipitated by: Drugs, infection, surgery, childbirth, tapering of immunosuppressants

 - Meds to Avoid: Fluoroquinolones, Magnesium, Anesthetics, Penicillamine, Beta blockers, Procainamide



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