Final answer:
A myasthenic crisis presents with severe muscle weakness due to disease exacerbation, whereas a cholinergic crisis is caused by medications and features excessive muscarinic signs. Differentiating the two can involve the administration of edrophonium but relies heavily on clinical presentation and patient history.
Step-by-step explanation:
Cholinergic crisis and myasthenic crisis are two conditions associated with myasthenia gravis (MG), a neuromuscular disorder. Clinically, a myasthenic crisis is characterized by severe muscle weakness leading to respiratory failure, and is caused by an exacerbation of the disease process itself. Conversely, a cholinergic crisis results from an overdose of acetylcholinesterase inhibitors and presents with signs of excessive muscarinic stimulation such as miosis (constricted pupils), salivation, diarrhea, bradycardia, and muscle fasciculations.
To differentiate between them, a test dose of edrophonium, a short-acting acetylcholinesterase inhibitor, can be administered. An improvement in muscle strength suggests a myasthenic crisis, whereas worsening symptoms indicate a cholinergic crisis. However, due to potential complications, this test is now less commonly performed, and the clinical presentation and history are relied upon instead.