Head tilt in rabbits can have a very dramatic presentation. In addition to the abnormal head position, ataxia, circling, and rolling can occur, and the owner is often very stressed and frightened by this, sometimes seemingly more so than the patient! Onset may be acute or gradual; any age and both sexes are equally affected.
Signs on physical examination can vary greatly. A patient may have a severe head tilt, Horner’s syndrome ,nystagmus, and have ataxia at home, yet be laterally recumbent in the exam room; or the patient may have a mild head tilt and no other abnormality. The top two differential diagnoses are Encephalitozoon cuniculi infection or otitis interna, and in some cases, both may occur. Other causes of vestibular disease in rabbits include neoplasia or bacterial meningoencephalitis, but these are comparatively rare. Otitis interna can occur with or without otitis externa. Seizures and paresis may be seen in cases of E. cuniculi, but do not occur with uncomplicated otitis interna. However, seizures can occur if there has been bacterial spread to the brain.
Diagnostic testing includes CT of the head for otitis interna and E. cuniculi serology- we prefer the University of Miami panel which includes IgG, IgM, and C-reactive protein. Ventrodorsal or lateral oblique skull radiographs are sometimes helpful for otitis interna, showing thickening of the lining of the bullae, but can also be non-diagnostic.
Treatments are usually initiated pending results. An antibiotic with gram-negative coverage and good bone penetrance such as enrofloxacin is a reasonable empirical choice for suspected otitis interna. Gram positives and occasional anaerobes have also been implicated. Antimicrobial treatment is generally greater than 4-6 weeks, and early discontinuation may result in treatment failure or antibiotic resistance. A partial ear canal ablation in rabbits has been recently described, which may be better tolerated in this species than the previously used TECA for recurring or unresolving cases. Because of the time involved in waiting for E. cuniculi results (can be up to 2-3 weeks), treatment is recommended to be initiated for the symptomatic rabbit. We prefer oxibendazole (20mg/kg q24h x 28d), as fenbendazole is not distributed to the CNS. Like any imidazole drug, oxibendazole can cause bone marrow suppression, and a CBC is recommended at day 14 and 28. An NSAID such as meloxicam may be given if ileus is not present, or once resolved. In patients that cannot receive meloxicam, analgesia such as buprenorphine should be considered for suspected otitis interna. Meclizine (12-24mg/kg PO q8-12hr) is an antihistamine which can be a very helpful anti-vertigo medication in any rabbit vestibular disease. Many of these rabbits remain willing to eat once their vertigo is somewhat controlled, but syringe-feeding is necessary for rabbits that are not eating, or that undergo ileus, a frequent sequela to any rabbit illness.
Environmental support may also be needed. Rabbits which are falling, rolling, or recumbent need a contained environment, preferably padded with fleece or toweling which is changed frequently to keep dry. Some rabbits seem to feel more secure when gently wedged into place with rolled towels, as it may give them another sensory impression to help counter vertigo. Frequent cleaning of the rabbit may be needed initially to prevent urine scald. Blepharoconjunctivitis of the “down” eye is common, and eye lubrication is usually warranted, or triple antibiotic ophthalmic ointment if the tissue is severely inflamed. Rabbits with otitis interna may exhibit Horner’s syndrome due to inflammation around the trigeminal nerve, and should be monitored closely for loss of palpebral reflex, which can result in exposure keratitis. Where otitis externa is present, the external ear canals should be cleaned as thoroughly as the patient will tolerate, as the thick mixture of caseous rabbit pus and ceruminous debris is not readily penetrated even by topical antimicrobials. A slender ear cone attached to an otoscope can be gently guided into the debris, where it will clog the cone. The cone is then removed and the process repeated as tolerated. A surprising amount of ceruminous, purulent debris can be removed this way without fear of pushing it deeper into the ear.
After initial diagnostic testing has been performed and any complications such as ileus addressed, the rabbit can often be managed at home, depending on its degree of debilitation, and the owners’ time and commitment to nursing care. I usually recommend the first recheck to be within one week of discharge. This ensures that the patient is tolerating treatments and responding appropriately, and that the owners are not overwhelmed by the amount of care their pet requires. If the rabbit and owners are doing well, subsequent visits may be scheduled two weeks apart, or more frequently if urine scald or corneal ulceration is seen.
By the first or second recheck examination, the E. cuniculi panel results should be available. If the rabbit is negative, oxibendazole is usually discontinued, particularly if otitis interna has been confirmed. Because false negatives can occur on the panel, this decision is made on a case-by-case basis, and may be continued if no other underlying etiology is found in a severely affected patient. If positive, oxibendazole is continued for 28 days, with monitoring for immunosuppression. Remember to alert clients of the zoonotic potential of E. cuniculi which has been reported in severely immunocompromised humans.
Successful treatment of otitis interna and/or E. cuniculi may take 2-3 months. Occasionally the head tilt does not completely resolve; however, many rabbits adjust well to even a significant head tilt, and there is no apparent impact on quality of life. Signs associated with uncomplicated E. cuniculi will often continue to resolve after oxibendazole has been discontinued. When a confirmed E. cuniculi positive rabbit has signs which plateau before complete resolution, a repeat E. cuniculi panel may be warranted. If the immuoglobulin titers or C-reactive protein levels are high, a repeat course of oxibendazole may be needed.
Owners will occasionally ask about risk to other rabbits in the household. Otitis interna is not readily transmitted, although an underlying predisposition, such as an upper respiratory infection, may easily be shared between housemates, with or without subsequent otitis. E. cuniculi can be transmitted between rabbits when shed in urine, and in my experience it is rare to have a symptomatic rabbit with a housemate that tests negative. Whether this is because of intra-household transmission, or because most rabbits have been exposed to E. cuniculi in their lifetimes is difficult to guess.
While a stressful presentation for patient and owner (and sometimes veterinarian) head tilt in rabbits can frequently be successfully managed with aggressive treatment of symptoms and underlying cause.
Contact Angell’s Avian and Exotic service at 617 989-1561 or firstname.lastname@example.org. You can also reach Dr. Simone-Freilicher at ESimoneFreilicher@angell.org.