HRS Article:   OLD RABBIT PARALYSIS PART IV: Strokes, Infections, Neoplasia (Cancer), and Systemic Disease

This is part IV continued from last issue.

Q. We have been told that our bunny has "old bunny paralysis" and nothing can be done. Is this true? What is this and why does it happen?

This is part four, the final in a series on the cause of paralysis or hind limb weakness in the rabbit. In part one vertebral spondylosis and trauma were discussed, in part two the one cell organism, Encephalitozoon cuniculi, was covered and in part three the raccoon roundworm, Baylisascaris procyonis, was explored. In part four I will cover a few other causes of hind limb weakness or paralysis including strokes, infections, neoplasia (cancer) and systemic disease.

STROKE
Cause: Strokes are not nearly as common in our pets as they are in humans. A stroke is a caused by either an obstruction of the flow of blood through a blood vessel in the brain or when a blood vessel ruptures and bleeds out into the surrounding brain tissue. Both "vascular accidents" can cause mild to severe brain tissue death.

Signs: The signs are dependent on where the damage takes place in the brain and may range from mild facial or extremity muscle weakness to complete paralysis of one or both sides of the body to sudden death. The incidence of strokes increases both in animals and people with age. Rarely, an animal can have a stroke following a surgical procedure due to a blot clot becoming lodged in a blood vessel in the brain.

Diagnosis: It is very difficult to diagnose a stroke in an animal without the sophisticated equipment available to humans. In humans, a diagnosis of stroke is made with one or more of the following procedures; arteriography (a radiographic dye study of the brain's blood vessels), CT (computed tomography) scan or MRI (magnetic resonance imaging). In animals a diagnosis of stroke is suggested based on ruling out other causes of disease.

Treatment: There is no treatment for a stroke. The only thing that can be done is to support the pet with fluids, assist feedings and pain medications if necessary. If the rabbit has lost the ability to control its bathroom habits, then it will have to have its bladder expressed several times a day and kept clean and dry. It can take weeks to months for the nerve tissue to heal and usually there is some degree of irreversible brain damage. You should discuss your bunny's prognosis with your veterinarian and decide what the best and most humane course of action should be for your pet.

BACTERIAL INFECTIONS
Cause: There are many bacteria that can cause infections in rabbits including the well-known Pasteurella multocida.. Bacteria can enter the fluid surrounding the brain and spinal cord (cerebrospinal fluid) or small abscesses can form in the brain or spinal cord itself. Both of these conditions are rare in rabbits. Infections of the inner ear are much more common and can also lead to hind limb weakness, but is usually also associated with a pronounced head tilt. We will discuss head tilts in rabbits in another issue.

Signs: The signs of infections of the central nervous system depend on the area being affected and the severity of the infection. The signs can range from depression, loss of appetite, high fever, collapse and partial or complete paralysis of the extremities.

Diagnosis: Often there is an increase in the number of white blood cells seen on a complete blood cell count. Another helpful diagnostic test is looking at microscopically and culturing at a sample of cerebrospinal fluid. In the case of an inner ear infection, there may be changes seen on an x-ray of the head (but not always).

Treatment: The treatment for a bacterial infection of the inner ear or central nervous system is antibiotics. The rabbit may need intensive care in the veterinary hospital including the placement of an IV catheter through which to give IV fluids and antibiotics. The prognosis for an infection of the central nervous system is guarded. The prognosis for an inner ear infection is much better, but in both cases there can be permanent nerve damage that may impair the rabbit's normal life style. As mentioned, nerve tissue takes a long time to heal and it may be weeks to months before any healing is apparent.

NEOPLASIA (CANCER)
Cause: Other than the high incidence of uterine cancer in female rabbits over two years of age, neoplasia of other organs is less common in rabbits than in other species such as humans, ferrets and dogs. The most common cancer in rabbits (outside of the uterine cancer mentioned) is lymphoma. Lymphoma can develop anywhere in the body and at any age. This cancer has been found in the spinal column where it causes damage to the spinal cord and the surrounding bone. Malignant cancers, such as uterine adenocarcinoma, can spread and develop new sites in the bony spinal column. Bone cancer has been noted in the rear legs of rabbits which also leads to hind limb weakness.

Signs: The signs of cancer can be variable dependent on the tissues being affected and may come on gradually or may appear suddenly.

Diagnosis: A diagnosis of cancer is often suspected on an x-ray and then confirmed with a biopsy of the affected tissue. Cancer in the brain or spinal tissue itself is more difficult to detect. Cancer in the bone causes dramatic changes that are easy to spot.

Treatment: Chemotherapy can be attempted if it is appropriate for the particular cancer. Another option is radiation therapy if you have such facilities in your area (often they are found at a veterinary school). If the cancer is in an extremity, it may be possible to amputate the limb to save the rabbit. Corticosteroids can sometimes slow the growth of the cancer and can be used to prolong life for a while.

SYSTEMIC DISEASE:
Any disease of a rabbit that causes it to feel weak can cause hind limb weakness and can be confused with a true neurological disease. Bunnies that are anemic or have heart disease, for instance, will not be able to get enough oxygen to their brain or muscle tissue and may appear weak and wobbly, particularly after exercise. Rabbits with liver or kidney disease can develop a buildup of metabolic toxins in their blood that interferes with normal brain and muscle function and thus leads to weakness. Malnutrition or a severely imbalanced diet can also lead to a generalized weakness. For instance, a lack of sufficient Vitamin E can lead to a type of muscular dystrophy and the inability to move properly. Any disease of a rabbit that causes pain on movement, may be incorrectly interpreted as hind limb weakness. For instance, pododermatitis (or sore hock...where the foot pads are raw and ulcerated) causes pain on movement, therefore the rabbit may sit hunched all day in its cage and appear to not be able to walk. Arthritic conditions of the spine (as we have mentioned in part one), hips, knees or hocks can cause an inability to move normally. Rabbits that are experiencing an intestinal shutdown either mechanically from an obstruction or physiologically from disease or inappropriate diet are often immobile due to the pain of the gas-filled intestinal tract and ultimately weakened by the disruption of the blood electrolyte balance. The diagnosis of any of these diseases depends on a combination of a good physical exam and history, and various diagnostic tests. The treatment, of course, is dependent on the diagnosis.


CONCLUSION:
We took a simple question about "old bunny paralysis" and took it to the extreme in this four part article! However, the point was to make you aware that there are many possibilities for hind limb weakness in a rabbit and often the diagnosis cannot be reached without some investigative work. Some of the conditions we have discussed are treatable and others are not. One of the most important parts of the investigative work of the veterinarian is the history. This is where you can help tremendously by being observant and even taking notes so you remember the details of your pet's illness or unusual behavior. This information is invaluable in determining a diagnosis, a treatment regimen and ultimately the prognosis for your pet.