Head tilt or torticollis, also known as “wry neck”, is a common emergency presentation of the pet rabbit (Oryctolagus cuniculus) (Fig 1). There are two common causes of head tilt or torticollis in the rabbit:
- Otitis media/interna secondary to bacterial infection. Bacteria commonly isolated from rabbits with otitis include Pasteurella multocida, Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus spp.
- Encephalomyelitits caused by Encephalitozoon cuniculi, an obligate, intracellular, microsporidian parasite commonly found in pet rabbits.
This paper will focus on distinguishing these two important differentials, however there are many other potential causes of head ataxia including: otitis externa, cerebral larval migrans caused by Baylisascaris procyonis (Furuoka 2003, Deeb 1994), listerioisis, toxoplasmosis, rabies virus infection (Karp 1999), or other conditions affecting the central nervous system such as trauma, lead toxicity, or neoplasia (Paul-Murphy 2007, Morgan 1994, Muller 2009, Sato 2011).
Signalment and history
- What is the rabbit’s breed? Many pet rabbit rabbits are mixed breeds, however clinical E. cuniculi infection may be more common in dwarf rabbits (Fig 2). Lop-eared rabbits lack normal ear drainage and are at particular risk for developing otitis (Fig 3).
- Describe the onset of disease.
The clinical presentation may be acute with otitis.
- Has there been a history of upper respiratory infection?
Rabbits with otitis may have a history of upper respiratory infection. Infection can spread from the nasal cavity to the middle or inner ear via the Eustachian tube.
- Is the rabbit strictly housed indoors?
Rabbits housed outdoors or in direct contact with wild skunk or raccoon are at increased risk for exposure to Baylisascaris, a less common differential diagnosis for torticollis (CDC 1981, Deeb 1994, Karp 1999). Unfortunately rabbits can also come into contact with raccoon or skunk feces through hay or bedding material.
- Is anyone in the household ill?
Herpesvirus infection is another rare but potential cause of neurologic disease in the rabbit. In one report, the owner reported a severe labial and facial herpesvirus infection 5 days before the onset of clinical signs in the rabbit (Muller 2009).
Perform a complete physical examination as clinical status allows. Evaluation may need to be performed in stages to minimize stress. Rabbits with torticollis or rolling may also benefit from placement in a small tub or box of appropriate size.
Otoscopic exam: Visualization of the horizontal ear canal and tympanic membrane can be difficult even in the normal rabbit. Sedation or general anesthesia may be needed for a thorough otoscopic examination if the ear is painful, or if the canal is filled with debris. With otitis media/interna, mucopurulent discharge may be observed behind the tympanic membrane or the membrane may even be ruptured.
Neurologic exam: Neurologic signs caused by E. cuniculi often include torticollis, nystagmus, ataxia, or rolling. Other neurologic signs may include seizures, a stiff rear gait, and posterior paresis. In rare instances, the rabbit may also exhibit ocular problems or renal signs of encephalitozoonosis such as urinary incontinence (Harcourt-Brown 2003).
Antemortem diagnosis of encephalitozoonosis can be challenging. Since latent infections are common, a positive antibody titer indicates infection but not active clinical disease. Consistent clinical signs paired with high serum antibody levels, or better yet, paired, rising titers support a presumptive diagnosis of encephalitozoonosis.
Culture of aural discharge is diagnostic when the tympanic membrane is ruptured in otitis media/interna (P-M 2007). Survey skull radiographs can also assist in the evaluation of the middle ears. Advanced diagnostics often relies upon alternate imaging such as computed tomography or magnetic resonance imaging.
Initial management of E. cuniculi infection relies upon administration of benzimidazoles, anti-inflammatory agents, and agents to reduce disorientation, such as meclizine.
- Benzimidazole anthelmintic (albendazole 30 mg/kg PO q24h x 30 days, fenbendazole 20 mg/kg PO q24h x 28 days)
- Non-steroidal anti-inflammatory agents (NSAIDs), such as meloxicam, have been tried in affected rabbits. Rabbits may be particularly sensitive to the immunosuppressive qualities of corticosteroids (Rosenthal 2004), and the use of corticosteroids in rabbits with E. cuniculi is controversial. A single dose of a short-acting corticosteroid such as dexamethasone (0.2-0.6 mg/kg SC) has been recommended for select cases. NSAIDs and corticosteroids should of course never be administered concurrently.
- Agent to reduce disorientation (i.e. meclizine 12.5-25 mg/kg PO q8-12h)(optional)
Initial management of otitis media/interna consists of topical treatment along with systemic management of pain and swelling.
- Ear lavage to remove debris found deep within the ear canal.
- Topical and systemic antimicrobial therapy (i.e. enrofloxacin, sulfa-trimethoprim, injectable procaine penicillin)
- Administer non-steroidal anti-inflammatory agents (NSAIDs to reduce inflammation and control discomfort in otitis. These drugs may be needed only at the very beginning of therapy. Avoid corticosteroids use (see above).
- Supplemental pain relief (e.g. opioids) may also be needed.
Do not forget supportive care. Depending on the onset and progression of disease, the rabbit may be dehydrated upon presentation. Provide fluid therapy and nutritional support as needed. Place food items directly in front of the rabbit.