Cholinergic crisis, myasthenic

The pronounced weakness that may result from inadequate therapy of myasthenia gravis (myasthenic crisis) can be distinguished from that due to anticholinesterase overdose (cholinergic crisis) by the use of edrophonium. In cholinergic crisis, edrophonium will briefly cause a further weakening of muscles, whereas improvement in muscle strength is seen in the... 

Symptoms of increasing muscle weakness may be due to cholinergic crisis (overdosage) or myasthenic crisis (increased disease severity) if crisis is myasthenia, patient will improve after 1-2 mg edrophonium if cholinergic, withdraw am-benonium and administer atropine... 

Since symptoms of anticholinesterase overdose (cholinergic crisis) may mimic underdosage (myasthenic weakness), their condition may be worsened by the use of this drug... 

These patients may also exhibit symptoms of excessive stimulation of muscarinic receptors (abdominal cramps, diarrhea, increased salivation, excessive bronchial secretions, miosis, bradycardia). Small doses of edrophonium (1-2 mg intravenously) will produce no relief or even worsen weakness if the patient is receiving excessive cholinesterase inhibitor therapy. On the other hand, if the patient improves with edrophonium, an increase in cholinesterase inhibitor dosage may be indicated. Clinical situations in which severe myasthenia (myasthenic crisis) must be distinguished from excessive drug therapy (cholinergic crisis) usually occur in very ill myasthenic patients and must be managed in hospital with adequate emergency support systems (eg, mechanical ventilators) available. 

Excessive dosing with an anticholinesterase can actually worsen the muscle weakness in myasthenics if the accumulation of acetylcholine at the neuromuscular junction is sufficient to cause depolarising blockade cholinergic crisis). It is important to distinguish this type of muscle weakness from an exacerbation of the disease itself myasthenic crisis). The dilemma can be resolved with a test dose of edrophonium, which relieves a myasthenic crisis but worsens a cholinergic one. The latter may be severe enough to precipitate respiratory failure and should be attempted only with full resuscitation facilities, including mechanical ventilation, at hand. 

A cholinergic crisis should be treated by withdrawing all anticholinesterase medication, mechanical ventilation if required, and atropine i.v. for muscarinic effects of the overdose. The neuromuscular block is a nicotinic effect and will be unchanged by atropine. A resistant myasthenic crisis may be treated by withdrawal of drugs and mechanical ventilation for a few days. Plasmapheresis or immimoglobulin i.v. may be beneficial by removing antireceptor antibodies (see above). 

Cholinesterase inhibitor very short duration of action (15 minutes). Used in diagnosis of myasthenia gravis and to distinguish myasthenic crisis from cholinergic crisis. 

It is of particular utility in the diagnosis ofmyasthenia gravis. It may also be employed to make a clear distinction between a myasthenic crisis and a cholinergic crisis, because in the first instance an improvement of neuromuscular function is usually observed while in the second it worsens it further. 

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