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Head tilts in rabbits (Proceedings)

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Aug 01, 2009

One of the more common abnormal presentations of disease in rabbits is a head tilt, which is often accompanied by nystagmus and circling. As in dogs, there may be multiple etiologies for head tilts. The etiology may be neurologic or vestibular, and it may be difficult to differentiate between these. This presentation is designed to aid the practitioner in differentiating neurologic from vestibular head tilts, as well as identifying and treating the more common etiologies.

When considering head tilts in rabbits, the most common differentials are Encephalitozoon cuniculi and otitis media/interna. However, central nervous system infection or abscess, or a neoplastic process, must also be considered. There are other etiologies such as toxoplasmosis or baylisascaris, but these are rare and often diagnosis is made post-mortem. In this section we will emphasize diagnosis and treatment of otitis, as well as differentiating otitis from central nervous system disease. Encephalitozoon cuniculi will be discussed in a separate section.

Rabbits with central nervous system disease will have signs in addition to the head tilt. These may include changes in mentation, proprioceptive deficits, gait abnormalities, abnormalities in reflexes, cranial nerve deficits, and ataxia in addition to the head tilt or head turn. With otitis, the lesion is peripheral. With peripheral lesions, the head tilt is always towards the side of the lesion, and if nystagmus is present, the fast phase is away from the side of the lesion. Horizontal nystagmus may be peripheral or central. Vertical nystagmus is always associated with central nervous system disease. With otitis, although the head tilt may be severe, there should be no proprioceptive or mentation abnormalities. However, many rabbits become very agitated, and so may seem duller or quieter, or conversely more agitated than normal.

Otitis

The anatomy of the rabbit ear canal is similar to other species. There is the pinna, and just cranial to the opening of the ear canal is a 'blind' pocket (called the pretragic incisure). There is a long vertical canal, and a short horizontal canal, and then the tympanum, which separates the external ear from the middle ear. The middle ear contains the ossicles, and the inner ear contains the semicircular canals and cochlea. The bulla lies at the base of the ear, and radiographically, the medial and lateral walls are very slightly thicker than the dorsal and ventral walls. The facial nerve runs near the bulla, with anatomic variation between individuals, so in some rabbits it may lie directly ventral to the bulla and in others it may be directly superficial to the bulla. Because of its anatomic location, in some rabbits with bulla osteitis, facial nerve contracture or paralysis may be present, and in any rabbit with asymmetric facial nerve examination, otitis and bulla disease should be considered.

Rabbits normally produce wax in the ear canals, which is brownish or slightly off-white and may serve a protective function. However, if the distal aspect of the canal cannot be visualized, it may be necessary to clean and remove this wax to facilitate more thorough otoscopic examination. (Note: ear mites have a crusty thick appearance, and when present can be easily diagnosed by obtaining a small swab sample and evaluating microscopically with mineral oil. Removal of these crusts and scales is not necessary; treat with ivermectin or selemectin and repeat in 2 weeks). If there is inflammation in the ear canal, or exudate which is white and creamy, perform a thorough otoscopic exam and evaluate the integrity of the tympanum. Obtain samples for cytology and culture, and evaluate cytologically for the presence of bacteria and/or yeast. If the tympanum is intact and the accumulation of exudate is mild, then any ear solution that does not contain steroids may be used to clean the ear canal. However, if the tympanum is ruptured, only warmed sterile saline should be used to clean the ear canal, as any fluid may have the potential to contact the brain.

Lop-eared rabbits are more prone to otitis. Common bacteria involved in otitis include Pasteurella multocida, Pseudomonas sp., Staphylococcus spp., and Streptococcus spp. However, many other bacteria may be present, so cultures should be obtained whenever possible. Yeast may also be present. Topical treatment should be initiated, using a product that does not contain steroid. In many patients, ophthalmic drops of an appropriate antibiotic can be used if an ear medication is not available without steroids. Standard yeast medications can be used. In many cases, systemic antimicrobials may also be necessary. Although steroids cannot be used, non-steroidal anti-inflammatory medications may be administered (including meloxicam, carprofen, ketoprofen, and topical NSAIDS).

For severe otitis media, deep ear lavage is beneficial to remove the debris. Because of the deep vertical canal, it is often impossible to reach the bottom of the ear canal with cotton swabs for cleaning. Deep ear lavage can be performed with a red rubber tube (3.5 to 8 French, use the largest size that will fit in the ear canal). Sedation or anesthesia may be required in painful or fractious rabbits. Using warmed sterile saline, and a syringe (20 cc for most rabbits), the canal is gently lavaged and suctioned, cleaning the debris and lavaging until the canal appears clear. If there is still debris which does not seem to b breaking up, then the procedure can be repeated several days later. Topical products designed to break down wax are available; again, choose only products without steroids.

If the infection is behind the tympanum, then a myringotomy can be performed. This is done endoscopically, to open the tympanum and lavage the middle ear. Again, sedation is required.

For severe otitis with head tilts, radiographs or CT scan should be performed to evaluate the bullae. Sedation is necessary. At least 4 views should be obtained; lateral, ventrodorsal, and right and left obliques. If possible, CT scan provides a greater degree of visualization and may detect more subtle changes or fluid. If bulla disease is present, bulla osteotomy (and total ear canal ablation, if indicated) can be considered. Although an aggressive surgery, it may ultimately alleviate long term pain as well as the need for repeated ear lavages.