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Differentials of acute flaccid paralysis
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I now have enough from authoritative sources to compile a thorough, well-organized answer. Here is the full differential:
Differentials of Acute Flaccid Paralysis (AFP)
AFP is defined as the sudden onset of weakness/flaccidity in one or more limbs, with reduced or absent deep tendon reflexes. The cause can be localized anatomically along the lower motor neuron (LMN) pathway.
1. Anterior Horn Cell (Spinal Cord - Gray Matter)
| Condition | Key Features |
|---|---|
| Poliomyelitis | Asymmetric, fever prodrome, no sensory loss, CSF pleocytosis; wild-type or vaccine-derived poliovirus |
| Non-polio Enteroviruses | EV-D68 (major cause of biennial outbreaks in USA since 2014), EV-A71, CV-A7; children, preceded by respiratory illness |
| Acute Flaccid Myelitis (AFM) | Predominantly children, fever + respiratory prodrome, onset of limb weakness within 10 days; MRI shows T2 lesions in gray matter |
| West Nile Virus | Asymmetric, fever, encephalitis possible; arboviruses can cause AFP |
| Rabies (paralytic form) | Ascending flaccid paralysis mimicking GBS; bulbar involvement; history of animal bite |
- Goldman-Cecil Medicine, block 51; Bradley and Daroff's Neurology, block 23
2. Nerve Roots / Peripheral Nerves (Polyneuropathy / Polyradiculopathy)
| Condition | Key Features |
|---|---|
| Guillain-Barre Syndrome (GBS/AIDP) | Most common cause of AFP globally; ascending paralysis, areflexia, preceding infection (Campylobacter, CMV, EBV); albumino-cytologic dissociation in CSF |
| Diphtheritic Polyneuropathy | Bulbar palsy first, follows Corynebacterium diphtheriae infection; palatal palsy, accommodation paresis |
| Traumatic Neuritis | Injection injury to sciatic nerve (gluteal injection); asymmetric |
| Lead/Arsenic/Organophosphate poisoning | Toxic neuropathy; history of exposure |
| Transverse Myelitis | Cord inflammation; sensory level present + sphincter dysfunction differentiates from pure AFP |
- Park's Textbook of Preventive Medicine, block 3; Red Book 2021; Bradley and Daroff's, block 23
3. Neuromuscular Junction
| Condition | Key Features |
|---|---|
| Botulism | Descending paralysis (cranial nerves first - diplopia, dysarthria, dysphagia); NO fever, NO sensory loss; bilateral CN VI palsy is a hallmark; pupillary involvement distinguishes from GBS |
| Myasthenia Gravis (acute exacerbation) | Fatigable weakness, ptosis, diplopia; worsened by exercise; anti-AChR antibodies |
| Lambert-Eaton Myasthenic Syndrome | Proximal weakness, autonomic features; improves briefly with repeated activity; associated with small cell lung cancer |
| Tick Paralysis | Ascending flaccid paralysis in children; caused by tick neurotoxin; resolves completely with tick removal; can mimic GBS |
- Harrison's 22E, block 18; Goldman-Cecil, block 44; Rosen's EM, block 24; Tintinalli's EM, block 15
4. Muscle (Myopathy)
| Condition | Key Features |
|---|---|
| Hypokalemic Periodic Paralysis | Episodic weakness; triggered by carbohydrates, rest after exercise; low serum K+; thyrotoxic form common in Asian males |
| Hyperkalemic Periodic Paralysis | Associated with myotonia; triggered by fasting or cold |
| Acute Myositis (viral/inflammatory) | CK elevation, myalgia, preceding viral illness |
| Rhabdomyolysis | Severe weakness, myoglobinuria, markedly elevated CK |
- Morgan and Mikhail's Anesthesiology, block 5
Quick Comparison Table: Key Distinguishing Features
| Feature | Polio | GBS | Botulism | Tick Paralysis | Trans. Myelitis |
|---|---|---|---|---|---|
| Fever | Yes (early) | No | No | No | Variable |
| Symmetry | Asymmetric | Symmetric | Symmetric (descend.) | Ascending | Symmetric |
| Sensory loss | No | Mild (paresthesias) | No | No | Yes (level) |
| Reflexes | Absent | Absent | Absent/reduced | Absent | Absent acutely |
| Cranial nerves | Bulbar only | Late | Early (CN VI, VII) | Rare | No |
| CSF | Pleocytosis | Alb-cyto dissociation | Normal | Normal | Cells + protein |
WHO AFP Surveillance Note
The WHO and national programs (e.g., India) require all cases of AFP in children <15 years to be reported and stool samples sent for polio testing, because early polio is clinically indistinguishable from GBS, transverse myelitis, and traumatic neuritis. - Park's Textbook of Preventive Medicine, block 3
Bottom line: The most common causes worldwide are GBS and poliomyelitis (or non-polio enteroviruses where vaccination is complete). Always consider botulism when cranial nerve palsies accompany descending weakness, and tick paralysis in children with ascending weakness - because tick removal is curative.
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