Causes and differentiation of paraparesis of the lower extremities

1. Big picture

Paraparesis means weakness of both lower limbs. It is a localization problem first and a disease diagnosis second.

For the neurology state exam, the central question is:

Is the paraparesis caused by an upper motor neuron lesion, a lower motor neuron lesion, a peripheral nerve/root lesion, a muscle disease, a neuromuscular junction disorder, or a functional disorder?

The most important clinical separation is:

• Spastic paraparesis → usually spinal cord / upper motor neuron pathway.
• Flaccid paraparesis → acute spinal shock, cauda equina, peripheral neuropathy, polyradiculoneuropathy, anterior horn cell disease, or muscle disease.

The dangerous causes are compressive spinal cord disease, cauda equina/conus syndrome, spinal epidural abscess, spinal infarction, trauma, tumor, and Guillain-Barré syndrome with respiratory/autonomic involvement.

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