Clinical scenario: Flaccid quadriparesis | Intact sensation | Raised CSF proteins
A 9-year-old boy is admitted with rapidly progressive weakness of both legs for 2 days, which has now involved both upper limbs. One week earlier, he had a self-limiting episode of bloody diarrhea. He is alert and afebrile.
Examination reveals:
- Symmetrical flaccid quadriparesis
- Muscle power: 2/5 in the lower limbs and 3/5 in the upper limbs
- Deep tendon reflexes are absent in all limbs
- Bilateral lower motor neuron facial weakness
- Sensation is intact
- No bowel or bladder dysfunction
Investigations:
- CSF (day 8): Protein 145 mg/dL, WBC 2 cells/mm³
- MRI spine: Normal
- Nerve conduction studies show:
- Markedly reduced CMAP amplitudes
- Normal sensory nerve action potentials
- Normal distal motor latencies
- No conduction block or temporal dispersion
- Mildly reduced motor conduction velocities
Which of the following is the most likely electrophysiological subtype of Guillain-Barré syndrome?
A. Acute inflammatory demyelinating polyradiculoneuropathy (AIDP)
B. Acute motor axonal neuropathy (AMAN)
C. Acute motor and sensory axonal neuropathy (AMSAN)
D. Miller Fisher syndrome
E. Chronic inflammatory demyelinating polyneuropathy (CIDP)
Correct answer & Explanation:
Correct Answer: B. Acute motor axonal neuropathy (AMAN)
Explanation:
This child has Acute Motor Axonal Neuropathy (AMAN), an axonal variant of Guillain-Barré syndrome that is particularly common in Asia and is frequently preceded by Campylobacter jejuni gastroenteritis.
The diagnosis is suggested by:
- Acute symmetric ascending weakness.
- Areflexia.
- Preserved sensation.
- Albuminocytologic dissociation in CSF.
- Nerve conduction studies showing:
- Reduced CMAP amplitudes (axonal motor injury).
- Normal sensory responses.
- No demyelinating features (no conduction block, no marked slowing of conduction velocity, no prolonged distal latencies).
Why the other options are incorrect
- A. AIDP: Characterized by demyelination with markedly slowed conduction velocity, prolonged distal latencies, F-wave prolongation, and conduction block.
- C. AMSAN: Involves both motor and sensory axons; sensory nerve action potentials are reduced.
- D. Miller Fisher syndrome: Presents with ophthalmoplegia, ataxia, and areflexia.
- E. CIDP: Progressive or relapsing neuropathy lasting more than 8 weeks, unlike the acute presentation here.
Learning Point
AMAN should be suspected in a child with acute flaccid paralysis following diarrheal illness when nerve conduction studies show isolated motor axonal involvement (low CMAP amplitudes with preserved sensory conduction and no demyelinating features). It is strongly associated with anti-GM1 antibodies and Campylobacter jejuni infection.
