Guillain-Barré for Step 1: CSF, Campylobacter, ALS & UMN

Creator: Progress Note
Published: 2026-08-29
Keywords: Guillain-Barre syndrome, guillain barre usmle, campylobacter guillain barre, albuminocytologic dissociation, gbs ivig plasmapheresis, umn vs lmn signs, als upper lower motor neuron, miller fisher anti gq1b, spinal cord lesions step 1, subacute combined degeneration

bolt The 60-second version

check_circleGBS is an acute immune attack on peripheral nerve myelin (or axons), often 1–3 weeks after Campylobacter jejuni gastroenteritis or a viral infection, via molecular mimicry.
check_circleSymmetric weakness that ascends from the legs, with lost reflexes, mild sensory symptoms, and often facial weakness.
check_circleAutonomic instability (arrhythmias, blood pressure swings) and respiratory failure are the main dangers; track vital capacity.
check_circleCSF shows albuminocytologic dissociation: high protein with a normal cell count.
check_circleTreat with IVIG or plasma exchange; corticosteroids do not help.
check_circleUpper motor neuron signs: spasticity, hyperreflexia, Babinski sign. Lower motor neuron signs: flaccid weakness, atrophy, fasciculations, hyporeflexia. ALS shows both.

target What you'll be able to do · aligned to USMLE Step 1 · Nervous System

NEUROExplain the triggers and pathophysiology of Guillain-Barré syndrome.
NEUROInterpret CSF and nerve conduction findings in GBS.
NEURODistinguish upper from lower motor neuron signs.
NEURORecognize ALS and the major spinal cord syndromes.

How GBS is tested on Step 1

A recent infection, then rapidly rising weakness without reflexes.

GBS course. Miller Fisher variant: ophthalmoplegia, ataxia, and areflexia with anti-GQ1b antibodies.

Diagnosis and treatment

Support the diagnosis, then protect breathing.

Step	Finding or action
CSF	High protein, normal white cell count (may be normal in the first week)
Nerve conduction studies	Slowed conduction, conduction block, or reduced amplitudes
Monitoring	Forced vital capacity and negative inspiratory force; cardiac telemetry
Treatment	IVIG or plasma exchange; supportive care and DVT prevention
Not helpful	Corticosteroids

A high CSF cell count suggests another cause, such as HIV or Lyme disease.

Upper vs lower motor neuron signs

These signs localize every weakness question.

UMN vs LMN. GBS is a peripheral (LMN) disorder; MS and stroke are UMN disorders.

Spinal cord and motor neuron disorders

Which tracts are hit determines the findings.

Disorder	Lesion	Features
Amyotrophic lateral sclerosis	Corticospinal tract and anterior horn (UMN + LMN)	Mixed signs, no sensory loss; SOD1 in some familial cases; riluzole
Spinal muscular atrophy	Anterior horn (LMN); SMN1 gene	Floppy infant, tongue fasciculations
Polio	Anterior horn (LMN)	Asymmetric flaccid paralysis after febrile illness
Subacute combined degeneration	Dorsal columns, corticospinal tracts	Vitamin B12 deficiency; ataxia, spasticity
Tabes dorsalis	Dorsal columns	Tertiary syphilis; sensory ataxia, Romberg sign
Syringomyelia	Central cord, anterior white commissure	Cape-like loss of pain and temperature
Brown-Séquard	Hemisection	Ipsilateral weakness and vibration loss, contralateral pain loss

Friedreich ataxia (GAA repeat) combines spinocerebellar and dorsal column degeneration with cardiomyopathy.

Worked example

Read the CSF.

functions Worked example — weakness after diarrhea

Two weeks after a bout of bloody diarrhea, a 30-year-old has tingling feet and weakness that climbs from the legs to the arms over 4 days. Reflexes are absent. CSF protein is 180 mg/dL with 2 white cells/µL. What is the diagnosis, the likely trigger, and the priority?

Ascending symmetric weakness with areflexia suggests acute peripheral nerve demyelination.
High CSF protein with a normal cell count is albuminocytologic dissociation.
Bloody diarrhea before onset suggests Campylobacter jejuni, which mimics nerve gangliosides.
The priority is to monitor vital capacity and start IVIG or plasma exchange.

Answer. Guillain-Barré syndrome after Campylobacter jejuni; monitor breathing and give IVIG or plasma exchange.

Next in the roadmap

Mood Disorders & Antidepressants

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quiz Test yourself

Quick check — 3 questions

1. The most important bedside measurement in a patient with GBS is:

2. A patient has hyperreflexia in the legs plus tongue fasciculations and hand atrophy, with normal sensation. Diagnosis?

3. Loss of pain and temperature across both shoulders with preserved touch suggests:

Frequently asked questions

What infection most often precedes Guillain-Barré syndrome?expand_more

Campylobacter jejuni gastroenteritis.

What is albuminocytologic dissociation?expand_more

High CSF protein with a normal white cell count, typical of GBS.

Are steroids used to treat GBS?expand_more

No. IVIG or plasma exchange is used.

Which disease has both upper and lower motor neuron signs?expand_more

Amyotrophic lateral sclerosis.

References & further reading

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