Intervertebral Disk Disease

July 13, 2011

Intervertebral disk disease is a common condition in pets that causes symptoms ranging from back or neck pain to total paralysis of the rear legs and occasionally all four legs. It can occur acutely or it can have a slow onset over a period of several days.

The intervertebral disk is located between the vertebral bodies. They provide flexibility to the spine and act as shock absorbers for the veliebral column. With age, the disks undergo one of two types of degeneration, chondroid or fibroid metamorphosis, which causes a loss of capacity to absorb shock. The center of the disk goes from a jelly-like material to a dry, gritty material. Normal wear and tear severely weakens the intervertebral disks especially in the thoracolumbar area of the spinal column.

The spinal cord is like an expressway from the brain to the rest of the body. Impulses travel back and forth between the various body parts and the corresponding part of the brain that controls it. Any interruption in the conduction of the impulses [protruded disk material] causes a malfunction in the body caudal to [behind] the lesion. It is similar to a car wreck during rush hour that stops traffic. A bad wreck stops all traffic while a less damaging wreck allows some traffic to trickle by. A severe bruise stops all the impulses while a less severe bruise allows some impulses to pass by. This is evidenced by the presence of deep pain in the toes of the rear feet and tone in the abdominal musculature.

There are two types of injury that occurs when a disk protrudes into the spinal canal. The concussive injury occurs when the disk material hits the spinal cord causing bruising. The grey matter in the center of the cord is primarily affected by this injury. The second type of injury is compression of the spinal cord caused by the prolapsed disk material's presence between the spinal cord and the wall ofthe vertebral body. As the cord swells, the compression gets worse and affects primarily the white matter in the cord. This is where the long tracks from the brain to the rest of the body are located. Communication between the brain and the body occurs by impulses going back and forth along these tracks. Any damage to the long tracks affects function of the body beyond the lesion. The spinal cord is like a telephone line. Everything works up to the point of a break in the line and nothing works past the break.

Injury to the cord sets off a cascade of events that leads to various degrees of loss of function to the body parts behind the site of the injury. The first to go is loss of proprioception which is evidenced by dragging of the rear feet, stumbling, or crossing the rear legs. Loss of motor function is the next level of injury followed by loss of superficial sensation and finally loss of deep pain sensation to the legs. If deep pain is lost, there is significant injury to the cord that may not respond to medical or surgical treatment. The most devastating type of spinal cord injury is myeolmalacia which is a melting of the spinal cord caused by disk protrusion which results in severe crushing of the cord. The ascending and descending loss of function is usually fatal or results in euthanasia of the pet.

Continue: "Back Pain in Your Dog May be Disk Disease"

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Intervertebral Disk Disease

July 13, 2011

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