Nursing care
Myasthenic crisis vs cholinergic crisis: how to tell them apart
Written and reviewed by Brian O'Connor, MSN, RN, CCRN · 4 min read · Updated October 2026
Short answer
Myasthenic crisis is weakness from too little effective acetylcholine signalling, often triggered by infection or undertreatment. Cholinergic crisis is weakness from too much anticholinesterase medicine, and it adds muscarinic signs: salivation, tearing, sweating, cramps, diarrhoea and muscle twitching. Both can stop breathing, so airway and breathing come first, before anyone works out which crisis it is.
The single most useful clue: muscarinic signs
Cholinergic crisis happens when anticholinesterase medicine such as pyridostigmine leaves too much acetylcholine at nerve endings. The excess also acts on muscarinic receptors, so the patient shows secretions and gut overactivity on top of weakness: drooling, tearing, sweating, abdominal cramps and diarrhoea, plus muscle twitching called fasciculations.
Myasthenic crisis is the opposite problem. Antibody attack on the neuromuscular junction leaves too little effective signalling, so the patient is weak, often with ptosis, double vision, a weak voice and poor swallowing, but without that wet, overactive picture. Infection, surgery, stress and missed or reduced doses are common triggers, so medication timing is a key history question.
Overlapping findings that cannot settle the question
Both crises cause generalised weakness, difficulty swallowing, a weak cough and respiratory muscle failure. Pooled saliva can appear in either, because a patient with myasthenic weakness may simply be unable to swallow secretions, so drooling alone is a weak clue. MSD Manuals notes that mild cholinergic crisis can be hard to distinguish from myasthenic weakness.
Heart rate is also unreliable. Many textbooks link muscarinic excess with bradycardia, yet MSD Manuals lists tachycardia in cholinergic crisis, and a distressed, hypoxic patient may be tachycardic for other reasons. The edrophonium (Tensilon) test that older resources describe for telling the two apart is no longer routinely performed, and edrophonium is not available in the United States.
Shared first priority: airway and breathing
Whatever the cause, the danger is respiratory failure, and it can develop quickly once breathing muscles start to fail. The nurse positions the patient upright, has suction ready, applies oxygen as ordered, and reports a rising respiratory rate, shallow breaths, a weak cough or a falling forced vital capacity at once.
Bedside measures of breathing strength, such as forced vital capacity, help the team spot impending failure early. Prepare for possible intubation and mechanical ventilation. Hold oral intake if swallowing is unsafe, because aspiration is a real risk in both crises. Working out which crisis it is happens alongside this support, not before it.
Nursing care that differs between the two
In suspected cholinergic crisis, anticholinesterase medicine is usually stopped for a period on medical orders, because more of it worsens the problem. Atropine may be ordered to block muscarinic effects; if so, the nurse watches for thickened secretions that are harder to clear. Report recent medication times and any extra doses taken at home.
In myasthenic crisis, treatment targets the immune attack and the trigger. Plasma exchange or intravenous immune globulin may be used, infection is treated, and medicines known to worsen myasthenia are reviewed. The nurse supports the airway, monitors vital signs and fluid balance during treatment, and gives medicines strictly on time once they are restarted.
Hypothetical practice scenario
Hypothetical scenario, not a real exam item: a client with myasthenia gravis took extra pyridostigmine doses at home because of worsening weakness. The nurse finds profuse saliva, sweating, abdominal cramping, twitching around the eyes and a weak cough. Which action comes first: give the next scheduled pyridostigmine dose, assess respiratory effort and prepare suction, or teach about medication timing?
Assessing breathing and preparing suction is the best first action, because airway compromise is the immediate threat. Giving the next pyridostigmine dose is the tempting distractor: the extra doses and muscarinic signs point towards cholinergic crisis, so more medicine could worsen weakness. Teaching matters, but it waits until the patient is stable.
Sources and further reading
MSD Manual Professional Version: Myasthenia Gravis. Definition and triggers of myasthenic crisis, muscarinic features of cholinergic crisis, edrophonium no longer used, forced vital capacity monitoring and stopping anticholinesterase medicine.
MedlinePlus: Myasthenia gravis. Weakness that worsens with activity, crises affecting breathing muscles after too much or too little medicine, and the role of pyridostigmine.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our neurological practice questions are the closest set to what this page covers.
Common questions
Which crisis is caused by too much medicine?
Cholinergic crisis. It follows excess anticholinesterase medicine such as pyridostigmine. Myasthenic crisis usually reflects worsening disease, often after infection, surgery, stress or missed doses. MedlinePlus notes that crises can follow too much or too little medicine, so the medication history is essential.
Can the Tensilon test still tell the two crises apart?
It appears in older textbooks, but the edrophonium test is no longer routinely performed and edrophonium is not available in the United States. Today the distinction rests on history, muscarinic signs and response to supportive care, decided by the medical team.
What should the nurse monitor most closely in either crisis?
Breathing. Watch respiratory rate and depth, cough strength, ability to swallow and speak, oxygen saturation, and forced vital capacity if ordered. A falling vital capacity or a weak cough can signal impending respiratory failure and needs prompt escalation.