Difference between myasthenic crisis and cholinergic crisis
Anticholinesterases (Neostigmine/Physostigmine) is the drug of choice for symptomatic management of MYASTHENIA GRAVIS. An excessive dose of an anti-ChE drug results in a cholinergic crisis.
Overtreatment with anti-ChEs
- If the dose of the antiChE is not adjusted according to the fluctuating requirement, relative overdose may occur from time-to-time.
- Overdose also produces weakness by causing persistent depolarization of muscle endplate, and is called cholinergic weakness.
Late cases with high anti-ChE dose requirements often alternately experience myasthenic and cholinergic weakness and these may assume crisis proportions. The two types of weakness require opposite treatments.
They can be differentiated by edrophonium test
Inject edrophonium (2 mg. i.v.)
- Improvement is seen in myasthenic crisis
- No improvement or worsening is seen in cholinergic crisis
WHY EDROPHONIUM IS USED FOR TENSILON TEST?
Edrophonium-a short acting anticholinesterase agent
1) Binding site of edrophonium to acetylcholine esterase: choline subsite of active center
2) No reaction with the enzyme: reversible binding only
3) Quaternary structure: rapid elimination
1) Binding site of edrophonium to acetylcholine esterase: choline subsite of active center
2) No reaction with the enzyme: reversible binding only
3) Quaternary structure: rapid elimination
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