## Pathophysiology of Poliomyelitis **Key Point:** Poliovirus causes paralysis through direct destruction of anterior horn motor neurons (lower motor neurons) in the spinal cord, not demyelination or toxin-mediated injury. ### Mechanism of Neuronal Damage 1. **Viral tropism**: Poliovirus has a specific affinity for motor neurons in the anterior horn of the spinal cord and brainstem motor nuclei. 2. **Cytolytic infection**: The virus replicates within motor neurons, causing cytolysis and neuronal death. 3. **Irreversible paralysis**: Unlike demyelinating diseases, motor neuron destruction is permanent, leading to flaccid paralysis with hyporeflexia. ### Clinical Correlation The **flaccid paralysis with hyporeflexia** (lower motor neuron signs) is pathognomonic for anterior horn cell involvement. If demyelination occurred (as in Guillain-Barré syndrome), we would expect ascending paralysis and preserved or hyperactive reflexes initially. **Clinical Pearl:** The symmetric lower limb paralysis in this case reflects bilateral anterior horn involvement. Bulbar poliomyelitis (affecting cranial nerve nuclei) can cause respiratory paralysis requiring mechanical ventilation. ### CSF Findings The **lymphocytic pleocytosis with normal glucose and protein** is typical of viral meningitis accompanying poliomyelitis. Glucose remains normal because poliovirus does not consume glucose like bacteria do. **High-Yield:** The key distinguishing feature is that poliovirus causes **motor neuron death**, not demyelination. This explains why recovery is limited and residual paralysis is common in polio survivors. [cite:Robbins 10e Ch 28]
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