MG CRISIS AND CH CRISIS

Myasthenic Crisis vs. Cholinergic Crisis

• Focused on the differences and similarities of these two crises as complications of myasthenia gravis.

Pathophysiology

• Neuromuscular Junction

  • A critical area where nerve fibers meet muscle fibers.

  • Stimulation of the cholinergic fiber by the central nervous system leads to the release of acetylcholine, a neurotransmitter.

  • Acetylcholine binds to nicotinic acetylcholine receptors on muscle fibers, resulting in muscle contraction.

• Myasthenia Gravis

  • An autoimmune disease where antibodies target nicotinic acetylcholine receptors, leading to muscle weakness due to reduced acetylcholine binding.

  • Acetylcholine Esterase: An enzyme that breaks down acetylcholine, which is essential for recycling acetylcholine to maintain muscle stimulation.

  • In myasthenia gravis, it's necessary to inhibit this enzyme to prevent the breakdown of acetylcholine, allowing increased availability for receptor binding.

Myasthenic Crisis

• Definition: Occurs due to low to absent stimulation at the neuromuscular junction by acetylcholine.

• Consequences:

  • Leads to severe muscle weakness and can result in respiratory failure.

  • Affects voluntary muscles involved in breathing, leading to inadequate respiratory function.

Cholinergic Crisis

• Definition: Results from excessive stimulation at the neuromuscular junction by acetylcholine.

• Consequences:

  • Constant stimulation of muscle fibers leads to muscle fatigue and severe weakness.

  • Also results in respiratory failure due to overstimulation.

Causes of Crises

• Myasthenic Crisis

  • Usually caused by:

  • Insufficient anticholinesterase medication dosages.

  • Acute exacerbation due to high stress (physical, mental, or from infections).

• Cholinergic Crisis

  • Caused by:

  • Excessive dosage of anticholinesterase medication leading to increased acetylcholine.

  • Results in overstimulation and crisis.

Signs and Symptoms

• Myasthenic Crisis

  • Dilated pupils

  • Increased heart rate and blood pressure

  • No cough or gag reflex due to weakness in throat muscles.

  • Risk of aspiration due to inability to swallow.

  • Incontinence of bowel and bladder due to weakened muscle control.

• Cholinergic Crisis

  • Signs of parasympathetic nervous system overactivity:

  • Constriction of pupils

  • Increased salivation and tears, leading to blurred vision.

  • Increased respiratory secretions, risking airway obstruction.

  • Muscle fasciculations (twitching from overstimulation)

  • Ultimately leads to flaccid paralysis, decreased heart rate, and decreased blood pressure.

Diagnosis

• Tensilon Test (Edrophonium Test)

  • Edrophonium is an anticholinesterase medication administered during the test.

  • Differentiates between the two crises based on patient responses:

  • Cholinergic Crisis: Administration of edrophonium worsens symptoms due to additional acetylcholine, resulting in a negative test result.

  • Myasthenic Crisis: Administration improves symptoms, leading to a positive test result.

Treatment

• Cholinergic Crisis Treatment:

  • Administer Atropine: An antidote to counteract the cholinergic overdrive.

  • Hold any further doses of anticholinesterase medication.

• Myasthenic Crisis Treatment:

  • Administer additional anticholinesterase medications to enhance acetylcholine availability at the neuromuscular junction.