MYASTHENIA GRAVIS (quick pearls)

8 Dec

Submitted by Amit Kumar, M.D.m_jpg0420f1

Quick Pearls:

Pathology: Auto-antibodies against ACh post-synaptic receptors

Common symptoms:

  • Ocular (ptsosis, diplopia),
  • bulbar (fatigable chewing, dysarthria, dysphagia),
  • loss of facial expessions,
  • neck/proximal limb weakness,
  • respiratory failure leading to myasthenia crisis (often tested via negative inspiratory force and vital capacity- NIF/VC)
  • Concerning if NIF and VC approach 25cmH2O and 15mg/kg body weight respectively.

 

Diagnosis:

-Bedside tests (higher risk for False+): Edrophonium “tensilon” test (acetylcholinesterase), ice-pack test

-Serum tests: ACh-R antibodies (more common), muscle-specific receptor tyrosine kinase (MuSK) antibodies

-Other: Repetitive nerve stimulation –> Fatigable

Complications:

-Thymic hyperplasia (85%), thymoma (15%). Prophylactic thymectomy recommended for <60y.

autoimmune thyroid dx (3-8%)

Treatment:

-Pyridostigmine (anticholinesterase)

-Chronic immunotherapies (glucocorticoids, azathioprine, cyclosporin, etc.)

-Rapid immunotherapies: plasmaphresis (usually every other day for total of 5 sessions), IVIG (total dose of IVIG is 2 g/kg, usually over 2-5 days)

Fun fact:

MANY medications are contraindicated in MG:
-Certain Antibiotics: Macrolides (Azithromycin, Erythromycin), Gentamicin, Kanamycin, Neomycin, Streptomycin, Tobramycin; Fluoroquinolones: Ciprofloxacin
-Cardiovascular drugs: Quinidine, Procainamide, Quinine Calcium channel blockers, Beta-blockers
-Neuromuscular Blocking Agents: Succinylcholine, d-tubocurarine or Any other neuromuscular blocking agent
-Narcotics: Meperidine, Morphine
-Any medication with the potential to suppress respiratory drive
Other medications: Iodinated contrast agents, Magnesium Preparations, Especially intravenous Magnesium but also PO such as Maalox, Steroids, Botulinum Toxin

***A good rule-of-thumb in generalized MG is to assume that any medication may exacerbate MG and to watch for worsening following the introduction of a new medication.

References:

  1.  Pal S, Sanyal D. Jaw muscle weakness: a differential indicator of neuromuscular weakness–preliminary observations. Muscle Nerve 2011; 43:807.<http://www.uptodate.com/contents/clinical-manifestations-of-myasthenia-gravis/abstract/20>
  2.  Lennon VA. Serologic profile of myasthenia gravis and distinction from the Lambert-Eaton myasthenic syndrome. Neurology 1997; 48:S23.<http://www.uptodate.com/contents/diagnosis-of-myasthenia-gravis/abstract/9>?
  3.  http://www.uptodate.com/contents/tests-of-respiratory-muscle-strength?source=search_result&search=NIF%2FVC+%2B+myasthenia+gravis&selectedTitle=1~150?
  4.  September 2015 EMRAP- Drugs not to use in Myasthenia Gravis

5. picture

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: