neurological disorders/conditions

My dog 3-4 days ago suddenly stopped eating (though he would drink some water) & then became lethargic & would not even get up to pee outside (we carried him in & out.) We took him to the vet who did an exam & his reflexes are obviously affected as is his balance (quite poor -- he can stand but is quite wobbly.)  She automatically went to assuming the worst case scenario (he has had some pain in his one shoulder over the last year which was assumed to be arthritis as bone cancer was ruled out because an anti-inflammatory seems to have great success & the x-rays showed just some arthritis) & thinks he probably has either a tumor of the nerve sheath or a degenerative disk disease.  I think it seems so sudden to assume this & considering his hyperactive nature (he is an aussie) that he may have just herniated a disk or something & is in great pain.  What are other possible causes of this condition & how likely is it that he has a major disease considering the SUDDEN nature of his decline?  We also wondered if its possible that contact with some type of poison could have this effect & she never really answered that question.  

[Aleda M Cheng, D.V.M., C.V.A]

There are many possible causes for your dog's condition including the ones that your veterinarian stated.  A spinal issue can be caused by any of the following:

1.  Intervertebral disc disease (ruptured or herniated disk). This is a painful condition and can cause limited reflexes.  This sometimes requires surgery.

2.  Bridging Spondylosis or spondylosis deformans.  Simply stated, spondylosis deformans occurs is the body's attempt to stabilize an arthritic spine.  However, as the bridging progresses over time it can cause pain and loss of function in the spine. This can cause limited reflexes and can be painful.

3. Old Dog Vestibular disease, This is an acute inflammation of the vestibular nerve that innervates the ear and stems from the brain.  This nerve controls balance and is also responsible for motion sickness.  This disease causes wobbliness as you described, a loss of appetite due to nausea (similar to motion sickness).  This does not usually cause limited reflexes.

4. Fibrocartilaginous emboli in which a piece of disk material breaks off, enters the circulatory system and blocks blood supply to the spinal cord.  This can be very painful when it first occurs, but afterwards this is usually a non-painful condition.  Definitely causes limited reflexes.

5. Degenerative myelopathy.  Which is loss of innervation to the spine due to an autoimmune or unknown etiology.  This is also a non-painful condition, definitely causes limited reflexes.

Nerve sheath tumor could also be a possibility as could a tumor on the spine as well as other less common causes.

Initial therapies that may help:
Steroids therapy to decrease inflammation
Robaxin or Diazepam as muscle relaxers
Tramadol as an adjunct pain medication
Anti-nausea medications to try to entice your dog to eat

Once the cause is definitely determined a definitive treatment can be instituted.  Physical therapy and Acupuncture can be helpful adjuncts to Disk Disease.

Taking your dog to a board certified veterinary neurologist may also be a good idea.