Presenting problem: Head Tilt and Rolling in Rabbits

Understanding head tilt and rolling in rabbits

Head tilt or torticollis, also known as “wry neck”, and uncontrolled or episodic rolling are common presentations for the pet rabbit (Oryctolagus cuniculus) (Fig 1).

Figure 1. Head tilt in a Dutch rabbit. Photo credit: C. Pollock. Click image to enlarge.

There are two common causes of head tilt and rolling 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. (Fisher and Carpenter 2012).
• Encephalomyelitits caused by Encephalitozoon cuniculi, an obligate, intracellular, microsporidian parasite commonly found in pet rabbits

This presenting problem article will focus on these two important differentials, however there are many other potential causes of head tilt including:  cerebral larval migrans caused by Baylisascaris procyonis (Furuoka et al 2003, Deeb and DiGiacomo 1994), listeriosis, toxoplasmosis, rabies virus infection (Karp 1999), or other conditions affecting the central nervous system such as trauma, lead toxicity, and neoplasia (Sato et al 2011, Muller et al 2009, Paul-Murphy 2007, Morgan 1994).

Key points of urgent care

Rabbits are often extremely stressed upon presentation and these patients can benefit greatly from the calm, quiet environment always recommended for prey animal species. Placing the rabbit in a small tub or box of appropriate size in a dimly lit area will also minimize rolling and minimize stress. Sudden movements or handling can startle the patient and instigate a rolling fit. Also protect the rabbit from hurting itself by using an enclosure that is well padded and free of hazards. In the rabbit with a head tilt, the eye facing the ground is at particular risk for injury.

To minimize stress, perform physical examination, supportive care such as fluid therapy and nutritional support, and diagnostic testing in stages.

Signalment and history

• What is the rabbit’s breed? Many pet rabbit rabbits are mixed breeds, however there are some anecdotal reports that 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).

Figure 2. Dwarf rabbits are popular house pets, which may explain the incidence of head tilt and rolling in this breed. Photo credit: Soccerspazz11 via Flickr Creative Commons.

Figure 3. Bacterial otitis may be more common in lop-eared rabbit breeds. Photo credit: C. Pollock. Click image to enlarge.

• Have any new rabbits been introduced recently?
• Are there any other in-contact rabbits with health concerns? Do any of these rabbits have a medical history consistent with E. cuniculi infection?
• Has there been a history of upper respiratory infection? Rabbits with otitis may have a history of upper respiratory infection as infection can spread from the nasal cavity to the middle or inner ear via the Eustachian tube.
• Is the rabbit housed strictly indoors? Rabbits housed outdoors or in direct contact with wild skunks or raccoons are at increased risk for exposure to Baylisascaris, a less common differential diagnosis for torticollis (Karp et al 1999, Deeb and DiGiacomo 1994, CDC 1981). Unfortunately rabbits can also come into contact with raccoon or skunk feces through hay or bedding material.
• Is there potential toxin exposure? Rabbits housed in older homes are at risk for ingesting lead-based paint.
• 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 severe labial and facial herpesvirus infection 5 days before the onset of clinical signs in the rabbit (Müller et al 2009).

Physical examination

Perform a complete physical examination, including otoscopic and neurologic evaluation, as clinical status allows. Diagnostics may need to be performed in stages to minimize stress. Rabbits with severe disease or those that do not tolerate handling may require sedation, such as butorphanol (0.2-0.5 mg/kg IM, SC) and midazolam (0.5-2.0 mg/kg IM) (Fiorello and Divers 2005).

Otoscopic exam: Visualization of the 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, as well as uncontrolled or episodic 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). It is important remember that most rabbits do not demonstrate a menace response.

Diagnostics

The minimum database should include a complete blood cell count (CBC) and biochemistry panel. Evaluate the CBC for an inflammatory leukogram and anemia, which may be seen with lead toxicity or anemia of chronic disease. Biochemistry results may include elevated liver enzymes. Fatty liver disease is common with prolonged anorexia and azotemia, consistent with dehydration or primary renal disease.

E. cuniculi testing:  Antemortem diagnosis of encephalitozoonosis can be challenging as definitive diagnosis requires histopathology or PCR (Harcourt-Brown 2010). Therefore E. cuniculi diagnostic testing is best left to the experienced rabbit veterinarian and does not need to be performed on an emergency basis.

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. Combining serology for IgM and IgG with tests for acute phase proteins appears to increase specificity of results (Cray et al 2015).

Microbiology:  Culture of aural discharge is diagnostic when the tympanic membrane is ruptured in otitis media/interna (Paul-Murphy 2007).

Imaging:  Survey skull radiographs can also assist in the evaluation of the middle ears. Advanced diagnostics, such as computed tomography or magnetic resonance imaging, further define disease or aid in the planning of medical and/or surgical therapy.

Therapy

Supportive care:  Depending on the onset and progression of disease, the rabbit may be dehydrated upon presentation. Rabbits with severe vestibular disease or those that have been anorexic are also prone to develop rabbit gastrointestinal syndrome (RGIS) or GI stasis. Provide fluid therapy and nutritional support via syringe or nasogastric tube as needed.

Otitis: Initial management of otitis media/interna consists of topical treatment, systemic medication for the pain and swelling, and in some cases, anti-nausea or motion sickness medications.

• Ear lavage to remove debris found deep within the ear canal. Since visualization is challenging, assume the tympanum is ruptured when selecting a cleaning solution.
• Topical and systemic antimicrobial therapy (i.e. sulfa-trimethoprim, enrofloxacin, injectable procaine penicillin)
• Administer non-steroidal anti-inflammatory agents (NSAIDs) like meloxicam (0.3 mg/kg PO q 24h) to reduce inflammation and control discomfort in otitis (Fiorello and Divers 2005). These drugs may be needed only at the very beginning of therapy, however do not administer NSAIDs to dehydrated or hypothermic patients or those with renal compromise. Avoid corticosteroids use as rabbits may be particularly sensitive to their immunosuppressive qualities  (Rosenthal 2004).
• Supplemental pain relief (e.g. opioids) may also be needed.
• Motion sickness medications like meclizine (12.5-25 mg/kg PO q8-12h) are indicated in the rolling rabbit.

Encephalitozoonosis:  Management of E. cuniculi is not indicated on an emergency basis unless the patient is deteriorating due to central nervous system disease with clinical signs such as altered mentation and seizure activity. Instead the patient should be referred to a veterinarian experienced in exotic companion mammal care.

Initial management of E. cuniculi infection relies upon administration of benzimidazoles, anti-inflammatory agents as well as 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) (Harcourt-Brown 2002, Suter et al 2001). Note: Benzimidazole toxicity has been reported in rabbits. Toxicity manifested as bone marrow suppression, hemorrhage, and death, particularly with long courses (Graham et al 2014).
• Non-steroidal anti-inflammatory agents, such as meloxicam, have been tried in affected rabbits. 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. Corticosteroids and NSAIDs should never be administered concurrently.
• Agent to reduce disorientation (i.e. meclizine 12.5-25 mg/kg PO q8-12h) (optional)

Summary

Head tilt or torticollis, also known as “wry neck”, is a common emergency presentation of the pet rabbit. Otitis media/interna and encephalomyelitis caused by Encephalitozoon cuniculi are important differentials for this presenting problem, and signalment, history, and physical examination findings can provide valuable clues. Additional diagnostic tools that can guide case management may include the minimum database and skull radiographs. Depending on the onset and progression of disease, the rabbit may be dehydrated upon presentation. Regardless of the underlying problem, supportive care such as fluid therapy and nutritional support is often indicated.

References