Anatomy

First let’s look at the anatomy and function of some vital areas in order to understand what does and does not contribute to head tilt in the rabbit.

External Ear

Disease in this area alone can cause head shaking, drooping ear and pain but does not cause a persistent head tilt or loss of balance. 

Middle Ear

Disease of the middle ear can cause head shaking, drooping ear and pain as well as deafness but does not cause a persistent head tilt. 

Inner Ear

The inner ear controls balance and hearing.  Signs of disease of the inner ear include deafness, head tilt, loss of balance and horizontal or rotary nystagmus. Proprioception (the ability to sense where the feet and legs are) and postural reactions (the ability to try to return to a normal standing position) are normal.  The rabbit will not act weak in other parts of the body and will continue to try to maintain normal body position even if it is difficult and the head is tilted. 

Brain

A specific area of the brain stem contains the vestibular nuclei, the origin of the vestibular nerve in the inner ear. The vestibular nuclei serve as the body’s central balance control. Signs of disease to this tiny area of the brain stem include head tilt, loss of balance, circling toward the affected side, rolling, vertical nystagmus, positional nystagmus, delayed or absent proprioception and loss of postural reactions.

Spinal cord

Head tilt is not a sign of primary spinal cord disease. 

Diseases Resulting in Head Tilt

A major differentiation that has to be made when diagnosing the cause of head tilts is whether it is peripheral (affecting areas other than the brain) or central (involving the brain and most specifically the vestibular nuclei).

Otitis Interna (Inflammation of the inner ear)

Causes can include the following: infectious disease, foreign bodies, trauma, neoplasia, and toxins. Signs of otitis interna include persistent head tilt toward the affected side, circling, nystagmus, ataxia (inability to walk normally), and deafness. The most accurate way to diagnose otitis interna is with a CT scan or MRI. A negative finding on an x-ray may not rule out otitis interna. 

Treatment for otitis interna depends on the primary cause, but since the majority of head tilts in rabbits are likely caused by bacterial otitis interna, it is advantageous to use a long-term course of antibiotics (3 to 6 weeks up to several months).  It is currently recommended to avoid the use of corticosteroids in rabbits. Rabbits may be more sensitive than other animals to developing immunosuppression when taking corticosteroids, either topically, orally or parenterally.

Otitis Media (Inflammation of the middle ear)

This is also a common disease of rabbits and may occur along with or even be the cause of otitis interna.  However, disease in this area alone does not cause a persistent head tilt.  Signs of otitis media include periodic head tilting and shaking. Diagnosis and treatment are generally the same as for otitis interna. 

Brain Stem Disease

Disease at the brain stem, specifically the vestibular nuclei, can cause similar signs as seen with inner ear disease.  Because the vestibular nuclei are deep in the brain, it is likely that disease affecting this area will also affect surrounding brain tissue.  Therefore, additional neurologic signs may be seen such as loss of appetite, mental dullness, paralysis and sudden death.  If the disease is also affecting the cerebrum, additional signs such as seizures can be seen. Bacteria, fungi and viruses can affect the brain stem.

Encephalitozoon cuniculi is a one-celled organism called a microsporidium that can infect rabbits. There is an ongoing controversy over the prevalence of E. cuniculi as a cause of primary head tilt in the rabbit.  It has been extremely difficult to demonstrate a definitive correlation between head tilt and active E. cuniculi infection.  Serological testing for E. cuniculi has some value but is not definitive and, if not interpreted appropriately may be misleading.  The only way to diagnose E. cuniculi as the definitive cause of a head tilt is to take brain tissue samples from the rabbit and find the organism and its damage in the microscopic samples.  No one has yet proven this correlation because a brain biopsy is dangerous for the rabbit and the E. cuniculi organism can be difficult to find in brain tissue. There are few, if any, case reports or studies definitely proving E. cuniculi is a significant pathogen in the rabbit nervous system. If a rabbit shows signs compatible with central vestibular disease, has a positive test for E. cuniculi, and all other diseases have been ruled out, some veterinarians will choose to treat for E. cuniculi empirically.  Proper and effective treatment for E. cuniculi is controversial. Some of the medications that have had been used to treat infection with E. cuniculi include albendazole, fenbendazole and oxibendazole.

The most common parasite associated with head tilt in a rabbit is the raccoon roundworm Baylisascaris procyonis.  Signs observed in rabbits with Baylisascaris may include head tilt, tremors, weakness, blindness, seizures or sudden death. Prevention of exposure to the parasite eggs is clearly the best way to counteract this disease.

Other causes of head tilt in rabbits may include cerebrovascular accident (stroke), cancer, trauma, toxins, metabolic disease, and heat stroke.

Diagnostic Approach to Head Tilt

History

A detailed history is of vital importance to determine the cause of disease. 

1. History of any prior illness
2. History any prior bouts with head tilt, weakness or incontinence
3. Possibility of exposure to environmental toxins or parasites
4. Exposure to other rabbits that are or were ill (particularly with neurological disease)
5. Possibility of trauma
6. Possible contact with human with active herpes viral infection

Physical Exam

A thorough physical exam and a thorough neurological exam is essential to diagnosing the cause of head tilt.

1. Mental attitude: Is the rabbit still alert and active, or dull and depressed?
2. Head tilt:  Look at persistence, side to which rabbit tilts, is circling involved?
3. Balance:  Does the rabbit try to right itself if given support?
4. Gait:  Any abnormalities in gait?
5. Nystagmus: If present, is it spontaneous or positional, is it horizontal or vertical?
6. Ear exam:  Are there signs of external or tympanic membrane disease?  Are there signs of fluid, blood or pus beyond the tympanic membrane?
7. Respiratory:  Are there signs of respiratory disease?
8. Systemic: Any other neurological signs, weakness (particularly hind limb), paralysis, incontinence, behavioral changes, external signs of trauma, particularly around the head and neck?   

Blood Tests

• Complete Blood Cell Count:  This test may be helpful to determine if there is anemia or infection.  
• Serum biochemistries:  These tests are helpful to rule in or out a number of metabolic diseases
• Serology for E. cuniculi – These tests are of limited use in definitively diagnosing active disease.
• Blood testing for heavy metals – These tests are particularly important if heavy metal intoxication is suspected.

Bacterial Cultures

Unfortunately, it is frequently not possible to safely or easily collect a sample to culture from a rabbit with vestibular disease.

Endoscopy

Endoscopy of the ear canal may be useful if middle ear infection is present, or possibly used to obtain cultures through the tympanic membrane with a surgical technique called myringotomy. 

Radiographs (X-rays)

Radiographs are useful to detect any heavy metal in the GI tract and for diagnosing head trauma.  Radiographs are also helpful in screening for disease of the tympanic bulla where the middle ear is housed

CSF (cerebrospinal fluid) Analysis

This may be useful if central disease such as encephalitis is suspected.

Biopsy

If it is possible to obtain a sample of the affected tissue, then a microscopic analysis can be extremely helpful in making a diagnosis.

CT scan or MRI

These imaging techniques are the most accurate and safest means of diagnosing disease of the inner and middle ear.

Treatment and Nursing Care

1. If a definitive diagnosis of the cause cannot be made (very common situation), but peripheral disease is the suspected due to physical exam, history and whatever diagnostics could be performed, the rabbit should be put on a course of broad spectrum antibiotics for an extended period of time ranging from 3 weeks to several months.
   
2. Generally, corticosteroids (cortisone-like drugs) should be avoided if possible, because rabbits may be especially sensitive to the immunosuppressive qualities of these drugs, and their use may cause further complications. 
   
3. If a diagnosis of E. cuniculi infection is strongly suspected based on multiple signs of central disease, serology, and ruling out other disease,  a short-term use of oxibendazole,  fenbendazole, or albendazole, can be considered. 
   
4. Non-steroidal anti-inflammatory drugs should be considered to reduce inflammation and control pain that may be present.  These drugs may be needed only at the beginning of therapy.
   
5. The use of anti-nausea drugs is controversial as there is no clear evidence that rabbits experience feelings of nausea.  There is no substantiated evidence that the use of anti-nausea drugs helps improve the condition of rabbits with head tilt.  Some veterinarians feel anti-nausea drugs, like diphenhydramine or meclizine, are useful in a rolling rabbit or one who is not eating.
   
6. Eye lubrication is useful, particularly in those animals that have a severe head tilt.  The down eye is prone to injury due to the protruding nature of rabbit eyes.  Rabbits do not blink often and this eye may become dry, abraded or infected.  Daily attention is necessary.
   
7. Fluid therapy and nutritional therapy (assisted feeding) may be necessary in any rabbit with vestibular disease.
   
8. Rabbits with vestibular disease from any cause often cannot access their cecotropes.  These nutrient-rich droppings can be collected while still moist and placed in a rabbit’s food bowl along with the pelleted food. 
   
9. It is essential to modify the environment of a rabbit with severe vestibular disease. This involves providing an enclosed padded or smooth-sided cage or enclosure. 
   
10. Aside from occasional anecdotal reports or testimonials, there is no evidence that any kind of physiotherapy or acupuncture will reduce the length of time a head tilt persists or will resolve a residual head tilt.
    
11. It is important to remember that the course of vestibular disease, even with the best prognosis, can take many weeks to months of committed care before improvement is seen. 
    
12. If a rabbit shows a continual decline or continued mental depression, loss of appetite or other weakness over a 2 to 3 week period, then the prognostic outlook is fairly grim and euthanasia should be a consideration. 

Prognosis

The prognosis for recovery from vestibular disease is variable, depending on the cause.  For most rabbits with peripheral disease, the prognosis is good to guarded. Some rabbits will have a lifelong residual head tilt even if the inner ear disease is cured. For rabbits with central vestibular disease the prognosis becomes guarded to poor for recovery to a sustainable state.

Key Points

1. Persistent head tilts accompanied by nystagmus and loss of balance are either peripheral (inner ear) or central (vestibular nuclei of brain).  
   
2. Peripheral vestibular disease is probably the most common cause of head tilt and is usually confined to head tilt, spontaneous nystagmus, circling and loss of balance.  The majority of cases are still mentally alert, maintain an appetite and do not exhibit other signs of weakness, gait abnormalities or seizures.
   
3. Peripheral vestibular disease is most commonly caused by inflammatory disease of the inner ear with bacterial disease being the most common.  There is no current evidence that E. cuniculi causes disease of the inner ear.
   
4. Peripheral vestibular disease carries a good to guarded prognosis for clinical recovery.  There is often a residual head tilt, but the rabbit can learn to re-establish balance and live a relatively normal life. 
   
5. Central vestibular disease is less common, and also includes head tilt, positional nystagmus, circling and loss of balance. 
   
6. Rabbits with central vestibular disease may also have histories of other signs compatible with central disease, potential exposure to toxins, parasites, or trauma.
   
7. Central vestibular disease may be caused by a variety of conditions including bacterial infections, E. cuniculi, parasites and trauma, and carries a guarded to poor prognosis for recovery. 
   
8. Radiographs are necessary to rule out trauma and may detect middle ear disease.  However, in many cases there will be no radiographic change even in middle or inner ear disease. Therefore, a negative x-ray is not proof that this disease does not exist.
   
9. CT scan or MRI is the most accurate and safe means of detecting inner ear disease as well as some types of central disease.
   
10. It is probably best at the minimum to treat rabbits with strictly peripheral signs that are confined exclusively to head tilt, nystagmus, circling and loss of balance with appropriate antibiotics because bacterial disease of the inner ear is common.
    
11. Non-steroidal anti-inflammatory drugs should also be considered in many head tilt cases to reduce inflammation (since inflammatory disease is so common in both peripheral and central disease) and reduce any pain. 
    
12. Appropriate nursing care for a rabbit with vestibular disease is crucial and requires a long-term commitment to both environmental and patient management.
    
13. The sooner you get veterinary care for a rabbit with vestibular disease, the greater the chances for successful resolution with a relatively short recuperative period.