In a patient with rapidly progressive symmetric limb weakness, ascending from the legs, areflexia, and recent infection, what is the likely diagnosis, appropriate diagnostic work‑up, and first‑line treatment?

Guillain-Barré Syndrome: Diagnosis and Management

This clinical presentation is Guillain-Barré syndrome (GBS), and you should immediately initiate intravenous immunoglobulin (IVIg) 0.4 g/kg/day for 5 consecutive days while simultaneously assessing respiratory function and arranging ICU-level monitoring. 1

Immediate Life-Threatening Assessment

Assess respiratory function NOW—approximately 20% of patients develop respiratory failure requiring mechanical ventilation, which can occur rapidly without obvious dyspnea. 2, 3

• Measure vital capacity, negative inspiratory force (NIF), and maximum inspiratory/expiratory pressures immediately and serially 2
• Apply the "20/30/40 rule": patient is at risk of respiratory failure if vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O 2, 3
• Single breath count ≤19 predicts need for mechanical ventilation 2
• Perform electrocardiography and continuously monitor heart rate and blood pressure for arrhythmias and autonomic instability 2

Diagnostic Confirmation

The diagnosis is primarily clinical but should be supported by ancillary testing. Do not delay treatment waiting for confirmatory tests. 2

Required Clinical Features

• Progressive bilateral weakness of arms and legs (initially only legs may be involved) 1
• Absent or decreased tendon reflexes in affected limbs 1

Strongly Supporting Features

• Progressive phase lasting days to 4 weeks (usually <2 weeks) 1
• Relative symmetry of symptoms 1
• Recent infection within 6 weeks (present in approximately two-thirds of patients) 2, 3
• Relatively mild sensory symptoms (paresthesias, distal sensory loss) 1
• Back or limb pain (affects approximately two-thirds of patients early in disease) 2

Diagnostic Work-Up

Cerebrospinal fluid (CSF) examination:

• Look for albumino-cytological dissociation (elevated protein with normal cell count <10 cells/μl) 1, 2
• Critical pitfall: Normal CSF protein in the first week does NOT rule out GBS—protein elevation typically appears at the end of the first week 2, 4
• CSF pleocytosis >50 cells/μl should prompt reconsideration of the diagnosis and evaluation for alternative causes like infectious polyradiculitis 1, 2

Electrodiagnostic studies (nerve conduction studies and EMG):

• Perform to support diagnosis and classify the neuropathy pattern 1, 2
• Look for sensorimotor polyradiculoneuropathy with reduced conduction velocities, reduced amplitudes, temporal dispersion, or conduction blocks 1, 2
• "Sural sparing pattern" (normal sural sensory nerve action potential with abnormal median/ulnar responses) is typical for GBS 1, 2
• Critical pitfall: Electrophysiological measurements may be normal when performed within 1 week of symptom onset—repeat study in 2-3 weeks if clinical suspicion remains high 1, 2

Laboratory testing:

• Complete blood count, glucose, electrolytes, kidney function, liver enzymes to exclude metabolic causes 1, 2
• Serum creatine kinase (CK)—elevation suggests muscle involvement and may indicate acute motor axonal neuropathy (AMAN) variant 2

First-Line Treatment

Initiate IVIg 0.4 g/kg/day for 5 consecutive days (total dose 2 g/kg) in patients unable to walk unaided within 2-4 weeks of symptom onset. 2, 5, 3

• Alternative equally effective option: Plasma exchange 200-250 ml/kg over 4-5 sessions 1, 2, 3
• Do NOT use corticosteroids for idiopathic GBS—they are not recommended 2
• Do NOT wait for antibody test results before starting treatment 2

Understanding Treatment Response

• Approximately 40% of patients do not improve in the first 4 weeks—this does NOT necessarily mean treatment failed, as progression might have been worse without therapy 2, 5
• Treatment-related fluctuations (TRFs) occur in 6-10% of patients within 2 months after initial improvement 2, 5
• If TRFs occur, repeat a full course of IVIg or plasma exchange 2
• If progression continues after 8 weeks from onset or patient has three or more TRFs, consider diagnosis of acute-onset chronic inflammatory demyelinating polyneuropathy (CIDP), which occurs in approximately 5% of initially diagnosed GBS cases 2

Critical Monitoring and Supportive Care

Admit to inpatient unit with capability for rapid transfer to ICU-level monitoring. 2

• Grade muscle strength using Medical Research Council scale in neck, arms, and legs 2
• Assess functional disability using GBS disability scale 2
• Test swallowing and coughing ability to identify aspiration risk 2
• Assess for facial weakness and ophthalmoplegia 2
• Check corneal reflex in patients with facial palsy to prevent corneal ulceration 2
• Monitor for dysautonomia including blood pressure/heart rate instability, pupillary dysfunction, bowel/bladder dysfunction 2, 5

Pain Management

Use gabapentinoids (gabapentin, pregabalin) or duloxetine for neuropathic pain—these can be initiated immediately alongside IVIg without interaction or contraindication. 2

• Do not delay gabapentin initiation waiting for IVIg to "work first"—pain control should begin immediately 2
• Consider tricyclic antidepressants or carbamazepine as alternatives 2

Medications to Avoid

Avoid medications that can worsen neuromuscular transmission: β-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolides 2

Features That Should Raise Concern for Alternative Diagnosis

• Marked, persistent asymmetry of weakness 1, 2
• Bladder or bowel dysfunction at onset or persistent during disease course 1, 2
• Fever at onset 1
• Sharp sensory level indicating spinal cord injury 1
• Hyper-reflexia, clonus, or extensor plantar responses 1
• Continued progression for >4 weeks after start of symptoms 1
• Alteration of consciousness (except in Bickerstaff brainstem encephalitis variant) 1

Prognosis

• 80% of patients regain independent walking ability at 6 months 2, 3
• Recovery can continue for more than 3 years, with improvement possible even more than 5 years after onset 2, 3
• Mortality is 3-10%, primarily from cardiovascular and respiratory complications 2, 3
• Advanced age and severe disease at onset are risk factors for poor outcome 2
• Arrange rehabilitation program with physiotherapist and occupational therapist as crucial step toward recovery 2