Two Dogs Unable to Walk But Very Different Localizations || Lower vs. Upper Motor Neuron Lesions

Dr. Wong evaluated two dogs with the same presenting complaint: sudden inability to walk in all four limbs. While their presenting problems were the same, their examinations had subtle but very important differences.

Acute onset of inability to walk in all four limbs can be causes by a problem affecting the spinal cord of the neck (called the C1-5, or cervical spinal cord) or by a problem affecting the nerves and/or muscles. These are called upper motor neuron (UMN) tetraparesis and lower motor neuron (LMN) tetraparesis.

It is imperative to tell the difference early, as it changes the list of possible causes, the diagnostic and treatment plan and the prognosis.

The distinction is made via the neurological examination. Dogs with LMN/nerve and muscle disease have decreased to absent spinal reflexes (withdrawal and patellar reflexes), while dogs with UMN/spinal cord disease have intact to increased reflexes. Dogs with LMN disease have decreased tone while dogs with UMN disease have increased tone.

The possible causes of LMN tetraparesis include: tick paralysis, botulism, fulminant myasthenia gravis, polyradiculoneuritis (coonhound paralysis), polymyositis (inflammation of the muscles) or less common causes such as coral snake envenomation.

Causes of UMN tetraparesis include slipped disks (IVDD), spinal tumors, fibrocartilagenous embolism (FCE), acute non-compressive nucleus pulposus extrusion (ANNPE), infection or inflammation of the spinal cord.

Tests for LMN disease may include blood tests, tick search, chest and belly X-rays (radiographs) spinal tap, electrodiagnostics, and possible muscle and nerve biopsy.

Tests for UMN disease include radiographs of the neck region, MRI of the neck and possible tap.

Prognosis depends on the underlying cause.

SEVNeurology.com

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