Ascending Weakness and a Falling Vital Capacity

Diagnosis: Guillain–Barré syndrome, acute inflammatory demyelinating polyneuropathy (AIDP) subtype.

Supporting features: progressive, symmetrical, ascending flaccid weakness over days; generalised areflexia; bulbar and facial involvement (nasal voice); an antecedent diarrhoeal illness three weeks earlier (Campylobacter jejuni is the commonest trigger); cytoalbuminological dissociation (protein 0.68 g/L with only 2 cells); and demyelinating nerve conduction (prolonged distal latencies, conduction block, absent F waves). Normal potassium, absence of a sensory level and flexor plantars argue against the main alternatives.

Alternatives to exclude:

• Hypokalaemic periodic paralysis - potassium 3.9 mmol/L, so excluded; also check magnesium.
• Myasthenia gravis - fatigable weakness, reflexes preserved, no sensory loss, prominent ptosis; anti-AChR or anti-MuSK if in doubt.
• Botulism - descending weakness, early cranial nerve palsies, dilated pupils; food history.
• Transverse myelitis or cord compression - sensory level, sphincter involvement, later spasticity; MRI whole spine if any doubt.
• Poliomyelitis or other enterovirus, West Nile virus - asymmetric, febrile, CSF pleocytosis.
• Acute intermittent porphyria - abdominal pain, psychosis, hyponatraemia; urine porphobilinogen.
• Vasculitic neuropathy, HIV seroconversion, diphtheria, tick paralysis, organophosphate poisoning, bilateral brainstem infarction.

Baseline tests: full blood count, urea and electrolytes, magnesium, glucose, creatine kinase, liver function, HIV, hepatitis serology, porphyria screen, antiganglioside antibodies (GM1; GQ1b if Miller Fisher features), stool culture and Campylobacter serology, chest radiograph, and MRI spine only if atypical. Do not delay treatment waiting for the CSF or nerve conduction studies - the clinical diagnosis is secure and treatment within two weeks of onset matters.

Setting. She needs a high-dependency or intensive care unit with continuous ECG, oximetry and non-invasive blood pressure, and 2–4 hourly forced vital capacity and single-breath count - not a general medical ward. Guillain–Barré syndrome kills through respiratory failure, aspiration and autonomic instability, all of which are predictable and monitorable.

Thresholds (the '20/30/40 rule').

• FVC <20 mL/kg. She is 1400 mL ÷ 64 kg = 21.9 mL/kg - already at the threshold, and FVC can fall by 30% within 24 h.
• Maximum inspiratory pressure weaker (less negative) than −30 cmH2O.
• Maximum expiratory pressure <40 cmH2O - a weak cough predicts secretion retention and atelectasis.
• Single-breath count <20. She manages 12, which correlates well with a low FVC.
• Bulbar dysfunction - nasal voice, facial weakness, difficulty swallowing, pooling of secretions. She already has two of these.
• Autonomic instability - BP 158/96 supine falling to 126/78 sitting, tachycardia 112. Labile blood pressure and arrhythmias are a recognised cause of sudden death.
• Rising PaCO2, falling saturation, exhaustion, inability to clear secretions.

Decision. Admit to ICU for monitoring now, with a low threshold for elective intubation before decompensation - a crash intubation in a patient with bulbar weakness and autonomic instability is far more dangerous than a planned one. Anticipate prolonged ventilation; tracheostomy if weaning exceeds about two weeks.

Alongside this: nil by mouth until swallowing is formally assessed, nasogastric tube, sitting up, chest physiotherapy, pressure-area care, and an explicit discussion of treatment ceiling with her and her family.

Disease-modifying therapy - start today.

• IVIG 0.4 g/kg/day for 5 days = 25.6 g/day for her (total 2 g/kg). Infuse per protocol; monitor renal function; check for IgA deficiency if there is any history of anaphylaxis; be alert to thrombosis and hyponatraemia (sucrose-containing preparations).
• Or plasma exchange, 4–6 exchanges of 40–50 mL/kg on alternate days over 1–2 weeks. The two are broadly equivalent; some analyses suggest a small advantage for plasma exchange in severe disease, offset by more hypotension and line complications. Never combine them.
• Corticosteroids are ineffective as monotherapy and adding them to IVIG confers no benefit.

Supportive care that changes outcome.

• Avoid suxamethonium - denervated muscle releases potassium and can cause fatal hyperkalaemia. Use non-depolarising agents cautiously with nerve stimulation; avoid intramuscular injections.
• Autonomic monitoring: treat labile hypertension and bradycardia cautiously with small aliquots of short-acting agents, avoid vagal stimuli, and watch for ileus, urinary retention and SIADH (check sodium daily).
• Venous thromboembolism prophylaxis with LMWH and compression stockings; pressure-area care; passive then active physiotherapy; splints to prevent contractures.
• Neuropathic pain: gabapentin or carbamazepine; avoid opioids that depress respiration.
• Anticipate and treat complications: aspiration pneumonia, atelectasis, constipation, depression, and the need for prolonged rehabilitation.

Prognosis to discuss with her. The nadir is usually reached within 2–4 weeks; recovery is slow, over months. About 80% walk independently by 6 months, though fatigue and residual weakness are common; mortality is around 3–7%, driven mainly by autonomic complications, sepsis and pulmonary embolism. A minority relapse with CIDP and need longer-term immunotherapy. Start rehabilitation planning early rather than at discharge.