Level 2 of 6Must-remember

Acute neuromuscular weakness

Assess, manage and stay safe — enough on its own

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The card — assess, manage, caution

Assessment— look, ask, measure

Two questions do most of the work: when was the patient last completely normal, and where did the weakness start and where did it go next — because tempo and direction of spread identify the disease more often than the examination does.
Read the pattern of spread: ascending symmetrically from the feet over hours to days with proximal as well as distal emphasis is Guillain–Barré syndrome (GBS); descending from the eyes and mouth downwards is botulism, neurotoxic envenoming or diphtheritic palatal palsy; fluctuating and worse towards the end of the day is myasthenia; sudden and maximal at onset is stroke; episodic lasting hours after a heavy carbohydrate meal or unusual exertion with complete recovery between attacks is periodic paralysis; and weakness preceded or accompanied by severe spinal pain with a sensory level and sphincter disturbance is cord compression.
Ask for the antecedent illness: GBS frequently follows a gastrointestinal or respiratory infection by one to six weeks, and Campylobacter jejuni is estimated to trigger 20–40% of all cases of GBS.
Measure the forced vital capacity (FVC) at the bedside and express it in mL/kg of actual body weight: a normal adult manages 60–70 mL/kg; 20 mL/kg or less is high risk; 15 mL/kg or less indicates intubation; and a falling FVC on serial measurement demands intensive monitoring and ventilatory support planning whatever the absolute value.
Use the bedside surrogates when no spirometer exists: single-breath count above 25 is broadly reassuring, 15–25 is a warning, and below 15 in an adult suggests a badly reduced vital capacity — a surrogate only, of limited precision, and not a substitute for spirometry.
The other respiratory cut-offs: maximum inspiratory pressure reaching −30 mmHg (approximately −40 cmH2O) indicates intubation, and maximum expiratory pressure below 40 cmH2O indicates a cough too weak to clear secretions.
Danger signs that demand immediate escalation: inability to lift the head from the pillow against gravity; paradoxical abdominal movement (the abdomen moving inward on inspiration) or intolerance of lying flat; a weak, breathy or wet cough, pooling of saliva, nasal regurgitation, a nasal or wet voice; a rising respiratory rate with shallow breaths or inability to complete a sentence in one breath; a falling vital capacity on serial measurement.
Rapid ascent and autonomic instability are equally alarming: arms involved within 24 hours of onset, swinging blood pressure, unexplained bradycardia, ileus or urinary retention.
Look for the compressive lesion in every patient: a sensory level, saddle anaesthesia or new sphincter disturbance is a compressive lesion until proven otherwise, and pyramidal signs, a markedly asymmetric deficit, a sharp sensory level or early sphincter involvement should suggest a focal cord lesion, not GBS.
Examine reflexes, tone, sensation and pupils: areflexia out of proportion to weakness with bilateral facial weakness suggests GBS; normal sensation with fatigable ptosis and asymmetric diplopia and normal pupils suggests myasthenia; dilated poorly reactive pupils with a dry mouth and descending paralysis suggest botulism; pinpoint pupils with salivation, lacrimation and bronchorrhoea suggest organophosphate poisoning.
Check the capillary glucose within the first minute — hypoglycaemia mimics every neurological presentation — and send potassium, calcium, magnesium and phosphate immediately, because these are the only causes in this chapter curable within the hour.Not available at your setup — Serum electrolytes.
In hypokalaemic periodic paralysis serum potassium is usually below 3.0 mmol/L during an attack, and acute hypokalaemia causes a flaccid paralysis reversed by potassium given slowly.Not available at your setup — Serum electrolytes.
Put every patient on continuous cardiac monitoring and do a 12-lead ECG, because both dysautonomia and electrolyte disturbance kill through rhythm: U waves and flat T waves in hypokalaemia, tented T waves in hyperkalaemia, bradyarrhythmia from dysautonomia.
Grade GBS disability with the Hughes scale: 0 healthy, 1 minor symptoms and able to run, 2 walks 5 m unaided but cannot run, 3 walks 5 m with aid, 4 bed- or chairbound, 5 assisted ventilation, 6 death — a grade of 3 or worse is the conventional threshold for immunotherapy.
Remember the arterial blood gas is for confirming a crisis, not predicting one: a normal PaCO2 in a patient with falling FVC is compensation, not reassurance, a rising PaCO2 is a very late finding, and a declining oxygen saturation is a late indicator of neuromuscular respiratory failure.Not available at your setup — Arterial blood gas.
Consider the mimics deliberately: hypoglycaemia, basilar artery occlusion (sudden, brisk reflexes, ocular and bulbar signs with consciousness possibly preserved), sepsis, hypercalcaemia, hyponatraemia and functional weakness — which is a diagnosis of positive signs (inconsistency, give-way weakness, Hoover's sign) and never one of exclusion in the acutely breathless patient.

Management— do this, in order

Sit the patient up and stop oral intake: nil by mouth until swallow has been assessed directly, sitting upright, with suction available — aspiration pneumonia is the commonest avoidable complication of bulbar weakness.
Write a schedule for serial respiratory measurement: hourly for progressing weakness, bulbar involvement or any measurement in the warning band; at least two-hourly for a stable patient in the first day. The trend matters more than any single number.
Attach continuous cardiac monitoring, because both dysautonomia and electrolyte disturbance kill through rhythm.
Correct the metabolic causes at once — glucose, potassium, calcium, magnesium and phosphate — since these are the only causes here curable within the hour.Not available at your setup — Serum electrolytes.
Acute hypokalaemic paralysis: replace potassium slowly — oral potassium chloride 20–40 mmol repeated according to response where swallowing is safe, and intravenous potassium chloride not usually exceeding 10 mmol/hour peripherally, higher rates only with central access and continuous ECG monitoring.Doctor / Nurse
Intubate at FVC 15 mL/kg, MIP −30 mmHg, or frank dyspnoea, and do not use non-invasive ventilation to avoid intubation in a patient whose vital capacity is falling; NIV may buy time in non-bulbar weakness only, under close observation and with an agreed intubation plan.Doctor / NurseNot available at your setup — Endotracheal intubation kit.
Two drug traps at intubation: suxamethonium can cause life-threatening hyperkalaemia in denervated or immobilised muscle from about 72 hours after the insult, and myasthenic patients are markedly sensitive to non-depolarising blockers while patients with Lambert–Eaton syndrome respond to them in a profoundly exaggerated and prolonged fashion.Doctor / Nurse
GBS immunotherapy — intravenous immunoglobulin (IVIg) 0.4 g/kg (400 mg/kg) intravenously once daily for 5 consecutive days, a total course of 2 g/kg, the same regimen for adults and children; indicated for inability to walk unaided (Hughes grade 3 or worse), or lesser disability with rapid progression or bulbar involvement.Doctor / Nurse
Plasma exchange is of equivalent efficacy — conventionally five exchanges over one to two weeks — and the choice is determined by availability, venous access and haemodynamic stability; combining the two confers no additional benefit.Doctor / Nurse
Do not give corticosteroids in GBS: treatment with prednisone is ineffective and may prolong recovery time.
Thromboprophylaxis in every immobile patient: enoxaparin 40 mg subcutaneously once daily in adults (20 mg daily if creatinine clearance is below 30 mL/min), or unfractionated heparin 5000 units subcutaneously every 12 hours, with graduated compression stockings.
Have atropine drawn up for dysautonomia: bradyarrhythmia may be provoked by tracheal suction and turning, so atropine 0.5–1 mg intravenously repeated to a maximum of 3 mg in adults (20 micrograms/kg, minimum 100 micrograms, in children) should be immediately available; marked hypotension may respond to volume replacement or pressor agents, and hypertension is labile and treated only if severe, with short-acting agents.Doctor / Nurse
Neuropathic pain, which is often the loudest complaint: paracetamol 1 g orally or intravenously six-hourly (maximum 4 g/day) with gabapentin 300 mg orally at night titrated upward, or pregabalin 75 mg orally twice daily; paediatric gabapentin starts at approximately 5 mg/kg/dose at night. Opioids must be used cautiously and sedatives avoided while respiratory reserve is falling.Doctor / Nurse
Myasthenic crisis needs a critical care environment where respiratory function can be monitored and ventilator support is readily available: seek and treat the precipitant (most often infection), stop offending drugs, and give rapid immunotherapy — IVIg 2 g/kg over 2–5 days or five plasma exchanges over one to two weeks.Doctor / NurseNot available at your setup — ICU / HDU bed.
Anticholinesterases in myasthenia: pyridostigmine 30–180 mg (average 60 mg) orally four times daily with a duration of action of 3–4 hours, or neostigmine 7.5–30 mg (average 15 mg) orally four times daily; if the patient cannot swallow, convert rather than omit — oral pyridostigmine 60 mg is approximately equivalent to neostigmine 0.5 mg intramuscularly or by slow intravenous injection, with cardiac monitoring and atropine available.Doctor / Nurse
Suspected cord compression is treated before imaging is complete: dexamethasone 10 mg intravenously can be given before an imaging study if there is clinical suspicion, continued at 4 mg every 6 hours orally until definitive treatment with radiotherapy and/or surgical decompression is completed; add gastric protection and monitor glucose.Doctor / Nurse
Image the whole spine urgently by MRI — up to 40% of patients presenting with compression at one level have asymptomatic epidural metastases elsewhere — and refer urgently for neurosurgical decompression and stabilisation; in cauda equina syndrome catheterise, record the residual volume and arrange urgent imaging and surgical decompression.
Care of the immobile patient carries at least as much survival benefit as immunotherapy: two-hourly repositioning, heel protection, lubrication or taping of an eye that will not close, mouth care, early enteral nutrition, bowel and bladder management, respiratory toilet and chest physiotherapy to prevent atelectasis, and physiotherapy from the first day.

Caution— what harms

Never wait for the oxygen saturation to fall: a declining oxygen saturation is a late indicator of neuromuscular respiratory failure because supplemental oxygen corrects the oximeter reading long before it corrects ventilation.
Never be reassured by a normal blood gas: a normal or low PaCO2 in a patient whose vital capacity is falling means the patient is still compensating by working harder, and when the respiratory muscles fatigue the carbon dioxide rises abruptly and arrest follows quickly.Not available at your setup — Arterial blood gas.
Never use non-invasive ventilation in bulbar weakness: secretions pool behind the mask, the airway is unprotected and deterioration is masked.Not available at your setup — Mechanical ventilator.
Never give suxamethonium to a patient denervated or immobilised for about 72 hours or more — it can cause life-threatening hyperkalaemia.Doctor / Nurse
Never give corticosteroids for GBS — prednisone is ineffective and may prolong recovery time; and never give both IVIg and plasma exchange, since combining them confers no additional benefit.
Do not exclude GBS on a normal early CSF: the high protein with normal cell count may take up to two weeks to develop, and a normal early CSF must not delay treatment; conversely a white cell count above 50 cells per microlitre should prompt consideration of an alternative diagnosis such as HIV, Lyme disease, sarcoidosis or lymphomatous infiltration of the roots.
Do not perform a lumbar puncture before imaging the spine in a patient with back pain, a sensory level or sphincter disturbance, nor at all in a patient too weak to maintain their airway curled on their side.
Check every drug before it is given in myasthenia: aminoglycosides and quinolones exacerbate neuromuscular blockade and should be avoided, and magnesium salts in any form, macrolides, penicillamine (which can itself cause a transient myasthenia), beta-blockers, quinine, quinidine, procainamide, all sedatives and opioids, and immune checkpoint inhibitors can convert a stable patient into a crisis.
High-dose corticosteroids can precipitate respiratory failure in myasthenia: some patients develop transient exacerbation of weakness and even respiratory failure within the first 1–2 weeks if corticosteroids are started at high dose such as prednisone 1 mg/kg/day, so in stable patients they are introduced gradually.
A good response to pyridostigmine is not reassurance: anticholinesterases relieve weakness but do not alter the natural history, and overmedication temporarily increases weakness — cholinergic crisis looks identical to the disease, the discriminators being muscarinic signs (salivation, lacrimation, sweating, abdominal colic, diarrhoea, bradycardia, small pupils) and fasciculations, and the safe response is to withhold the next anticholinesterase dose and support airway and ventilation.
Avoid aminoglycosides in botulism as they potentiate the blockade, and remember that antitoxin arrests progression but does not reverse established paralysis, so delay costs ventilator days.
Do not replace potassium fast or generously in periodic paralysis: total body potassium is normal and the ion has merely shifted intracellularly, so rebound hyperkalaemia is a real hazard and replacement must be conservative and frequently rechecked; acetazolamide sometimes helps prevent attacks in the familial form but may worsen the thyrotoxic one.
Do not manipulate the neck where cervical compression is suspected, and log-roll only; do not delay steroids and imaging in a cancer patient with new back pain because paraplegia established for more than 24–48 hours rarely reverses.
Do not diagnose functional weakness in the acutely breathless patient by exclusion — it is a diagnosis of positive signs (inconsistency, give-way weakness, Hoover's sign) — and never sedate an anxious, fully conscious, near-totally paralysed patient in place of explanation, orientation and analgesia.

Refer / escalate

Escalate to critical care immediately for a falling vital capacity whatever the absolute value, FVC 20 mL/kg or less, FVC 15 mL/kg or less, MIP reaching −30 mmHg, bulbar weakness with pooling secretions, autonomic instability or myasthenic crisis; and refer urgently for neurosurgical decompression in any patient with a sensory level, saddle anaesthesia, retention of urine or suspected cord compression, having first given dexamethasone 10 mg intravenously.

The card — assess, manage, caution

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