10.3 Acute Flaccid Weakness & Neuromuscular Emergencies (Guillain-Barré, Myasthenic Crisis)
Key Takeaways
Follow bulbar function, cough and ventilation in acute flaccid weakness. Serial mechanics help when the child can perform them reliably.
Progressive bilateral weakness with pain, reduced reflexes and autonomic lability suggests GBS. Early normal CSF protein does not exclude it.
Falling vital capacity and weakening inspiratory pressures support early escalation. A less negative NIF reflects weaker inspiration.
For ventilated myasthenic crisis, use rapid immunotherapy with IVIG or plasma exchange and consider holding pyridostigmine when secretion burden is substantial.
Treat suspected infant botulism with program-directed BabyBIG without waiting for lab confirmation. Report suspected AFM with spinal gray-matter involvement promptly.
Acute Flaccid Weakness and Neuromuscular Emergencies
Start with airway protection and ventilation while localizing the weakness. Check the trajectory, symmetry, tone, reflexes, sensation, cranial and bulbar function, and bladder symptoms. An ineffective cough, pooling secretions or progressive shallow breathing can precede a fall in oxygen saturation. Arrange critical care and neurology assessment early. Use serial forced vital capacity (FVC) and inspiratory and expiratory pressures when the child can cooperate. In an infant or child unable to perform reliable spirometry, follow cry or voice, cough, head control, chest and abdominal motion, secretions, and ventilation. Escalate for a deteriorating airway or ventilation even without a reliable mechanics value.
| Pattern | Likely localization and first decisions |
|---|---|
| Bilateral progressive weakness, often ascending, with pain or paresthesias and reduced reflexes | Guillain–Barré syndrome (GBS), a peripheral nerve/root disorder. Track ventilation and autonomic function. |
| Fluctuating ptosis, diplopia or bulbar weakness that worsens with use, usually with preserved pupils, sensation and reflexes | Myasthenia gravis, a postsynaptic junction disorder. Evaluate secretion clearance and ventilatory reserve. |
| Infant with constipation, weak suck or cry, ptosis, sluggish pupils and descending hypotonia | Infant botulism, a presynaptic toxin effect. Support airway and consult for antitoxin immediately. |
| Abrupt asymmetric limb weakness, often after a febrile respiratory illness, with reduced reflexes in affected limbs | Acute flaccid myelitis (AFM). Obtain spine MRI and involve neurology and public health. Consider polio when exposure or immunization history raises concern. |
| Weakness with a sensory level or new bowel or bladder dysfunction | Consider spinal cord disease, including transverse myelitis and compression. Obtain urgent spinal imaging. Reflexes may initially be depressed during spinal shock. |
Guillain–Barré Syndrome
A preceding gastrointestinal or respiratory infection is common. Campylobacter is one recognized trigger. Immune responses can injure peripheral myelin or axons, so a clinical GBS presentation alone does not identify the electrophysiologic subtype. A young child may first refuse to walk because of pain or weakness. Reflexes are usually reduced, though some variants retain reflexes. Ophthalmoplegia, ataxia and areflexia suggest Miller Fisher syndrome, for which anti-GQ1b testing can support the diagnosis. CSF may show elevated age-adjusted protein without substantial pleocytosis. Normal early protein does not exclude GBS. Marked CSF pleocytosis should prompt investigation of alternatives. Nerve conduction studies can support diagnosis and subtype, and may need repeating if obtained early. EAN/PNS guideline · Pediatric prospective cohort
Breathing and autonomic risk. An older cohort described the 20/30/40 warning values: vital capacity below 20 mL/kg, inspiratory pressure magnitude below 30 cm H₂O or expiratory pressure below 40 cm H₂O. The 2023 EAN/PNS guideline identifies FVC below 20 mL/kg, inspiratory pressure magnitude below 40 cm H₂O, expiratory pressure below 30 cm H₂O, or an FVC decline over 30% as predictors of need for ventilation. Use the trend and clinical exam. A negative inspiratory force of −22 cm H₂O represents less inspiratory strength than −35. In a child whose FVC drops from 26 to 18 mL/kg, the decline is (26 − 18) ÷ 26, or about 31%. A weak cough or unsafe swallowing in this setting supports controlled airway management before a crisis. Avoid succinylcholine when GBS-related denervation is suspected because of severe hyperkalemia risk. Individualize the airway plan with critical care and anesthesia. Original respiratory cohort · EAN/PNS guideline · Succinylcholine label
Telemetry and frequent blood pressure assessment help detect dysautonomia, including alternating hypertension and hypotension, tachyarrhythmias or profound bradycardia. Severe lability can justify invasive monitoring. Follow bowel and bladder function. Address hemodynamic changes with the ICU team, recognizing that large swings can follow suction or other stimulation.
Disease-directed treatment. Start IVIG or plasma exchange for severe or rapidly progressive GBS with specialist input. A standard IVIG course is 0.4 g/kg daily for five days, totaling 2 g/kg. The EAN/PNS guideline favors that course over a two-day course, and a small pediatric trial found more transient deterioration in the two-day group. Plasma exchange is an alternative, with pediatric dosing and access planned by the apheresis team. Corticosteroids are not recommended as GBS treatment. EAN/PNS guideline · Pediatric IVIG trial
Myasthenic Crisis and Cholinergic Toxicity
Myasthenia gravis causes fatigable weakness through postsynaptic junction dysfunction, often involving AChR or MuSK antibodies. Serology and specialist electrophysiology support diagnosis. Acute infection and medications can precipitate worsening. The ciprofloxacin boxed warning identifies risk of exacerbating myasthenia. Aminoglycosides and IV magnesium can impair transmission. Review these exposures and use alternatives when feasible. Assess medication toxicity if weakness follows an increase in pyridostigmine and is accompanied by miosis, diarrhea, fasciculations or excessive salivation and bronchial secretions.
Severe bulbar weakness, poor secretion clearance or declining ventilation warrants airway protection. In an intubated patient with significant secretions, temporarily holding pyridostigmine is often appropriate, with restart planned as strength improves. Use IVIG or plasma exchange for rapid immunotherapy, taking hemodynamics, access and comorbidities into account. If cholinergic toxicity is suspected, hold the excess agent and support ventilation. Atropine treats significant muscarinic effects such as bradycardia or bronchorrhea, while ventilatory support addresses weakness. International MG consensus · MGFA medication guidance · FDA ciprofloxacin label
Infant Botulism
In infant botulism, swallowed spores can colonize the gut and produce toxin that blocks acetylcholine release. Constipation, poor feeding, weak cry, ptosis and descending weakness are clues. Honey exposure supports suspicion, and its absence does not exclude disease. Assess airway protection immediately. In the U.S., contact the California Infant Botulism Treatment and Prevention Program for clinical consultation and access to BabyBIG. Notify the state health department and obtain stool or an appropriate enema specimen with public health laboratory guidance. Start antitoxin when clinically supported without waiting for test confirmation.
Verify the product lot. FDA specifies 20 mg/kg (0.4 mL/kg) as a single IV infusion for BabyBIG Lots 7 and 8, superseding the earlier 50 mg/kg dose for those lots. The October 23, 2026 Lot 8 notice also specifies the supplied sterile 0.2-micron filter. Confirm the supplied lot and its instructions with the dispensing program. In the original randomized trial, human botulism immune globulin shortened hospitalization and mechanical ventilation. Antibiotics do not treat intestinal infant botulism. Treat a separate bacterial infection when indicated with specialist guidance, avoiding aminoglycosides when feasible because they can worsen neuromuscular blockade. FDA Lot 7 notice · FDA October 23 Lot 8 notice · CDC infant botulism · CDPH clinical FAQ · Antitoxin trial
Acute Flaccid Myelitis, Polio and Transverse Myelitis
AFM can produce abrupt asymmetric weakness, reduced reflexes, and bulbar or respiratory involvement. Obtain spine and brain MRI with and without contrast as appropriate. AFM may show spinal gray-matter lesions. An MRI in the first 72 hours can be unrevealing. Discuss repeat imaging if suspicion persists. Obtain respiratory, stool, serum and CSF specimens promptly when safe. Enterovirus D68 is associated with AFM, but a positive PCR is not required for the clinical syndrome or for reporting a patient with acute flaccid limb weakness and gray-matter involvement. CDC advises reporting such a patient promptly to state or local public health. Use Standard plus Contact and Droplet Precautions per interim CDC guidance. Monitor respiration and swallowing, provide supportive care and start rehabilitation planning. CDC finds insufficient evidence to prefer or avoid IVIG, corticosteroids or plasma exchange for AFM itself. Evaluate and treat alternative diagnoses in parallel. If paralytic polio is suspected, contact public health immediately and arrange early paired stool and throat samples as directed. CDC AFM testing · CDC AFM precautions · CDC AFM treatment · CDC polio reporting
For suspected transverse myelitis, a sensory level or sphincter dysfunction favors a cord localization. Exclude compression urgently with MRI and assess inflammatory or infectious causes with neurology. Corticosteroids may be used for inflammatory transverse myelitis. Plasma exchange can be considered when the response to corticosteroids is inadequate. AAN transverse myelitis guideline
A 7-year-old has progressive symmetric weakness, absent reflexes, back pain and labile BP after diarrhea. FVC falls from 26 to 18 mL/kg, NIF is −22 cm H₂O and the child can no longer clear secretions. Which action is most appropriate?
Intubate using succinylcholine and start methylprednisolone for presumed GBS.
Use high-flow nasal oxygen and pyridostigmine and recheck spirometry the next day.
Arrange controlled intubation with critical care, avoid succinylcholine, monitor hemodynamics closely and begin IVIG or plasma exchange for severe GBS.
Wait for hypercapnia to confirm respiratory failure before escalating care.
An adolescent with generalized myasthenia develops ptosis, shallow breathing and inability to manage secretions after treatment for an infection with ciprofloxacin. The child takes pyridostigmine. Which management plan fits the presentation?
Increase oral pyridostigmine immediately and give IV magnesium for the weakness.
Give unmonitored edrophonium to decide if ventilation is needed.
Switch to gentamicin and defer airway support until hypercapnia appears.
Secure the airway, review triggering drugs and infection, hold pyridostigmine initially while ventilated with substantial secretions, and start IVIG or plasma exchange.
A 4-month-old has constipation followed by poor suck, ptosis, sluggish pupils and descending weakness after honey exposure. The team is supporting the airway, the California program supports infant botulism and pharmacy confirms BabyBIG Lot 8. What is the next disease-specific treatment?
Administer BabyBIG 20 mg/kg (0.4 mL/kg) once IV using the supplied 0.2-micron filter. Coordinate stool testing and public health reporting without delaying antitoxin.
Administer BabyBIG 50 mg/kg using the earlier package dose for Lot 8 and wait for the stool toxin result.
Give ampicillin and gentamicin to eradicate intestinal botulism before requesting antitoxin.
Start pyridostigmine and defer antitoxin until electrodiagnostic confirmation.
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