Floppy Rabbit Syndrome

Basic Information

Definition

Floppy rabbit syndrome (FRS) is a descriptive term for a condition with multiple possible origins. It is characterized by sudden onset of flaccid paresis or paralysis of all four limbs.

Synonyms

Generalized muscular weakness, flaccid paresis

Epidemiology

Species, Age, Sex

• The condition affects rabbits only.

• No age or sex predisposition is known.

Risk Factors

Risk factors vary depending on the exact origin involved. Trauma, dietary vitamin E deficiency, exposure to toxins, and generalized systemic disease leading to electrolyte disturbance are possible risk factors.

Contagion and Zoonosis

• One differential diagnosis for FRS is botulism. This and other toxins may affect other animals, but only if the rabbit is subsequently consumed. Steps should be taken to avoid this possibility.

Geography and Seasonality

• No seasonal incidence of this syndrome is known.

• FRS has been reported in Europe, North America, Asia, and Australia.

Associated Conditions and Disorders

FRS may be related to nutritional muscular dystrophy due to vitamin E deficiency. Lack of mobility and possible lack of appetite seen in FRS may cause or exacerbate gastrointestinal hypomotility.

Clinical Presentation

Disease Forms/Subtypes

• FRS has multiple possible causes.

• It resembles conditions such as spinal trauma and splayleg.

• It can be mistaken for sudden collapse due to general systemic disease.

History, Chief Complaint

Typically, rabbits with FRS present with sudden onset of generalized muscular weakness and a reduced but variable response to external stimuli.

Physical Exam Findings

• Flaccid paresis or paralysis

• Inability or reduction in ability to lift the head or move the limbs

• In nearly all cases, no other clinical abnormalities are noted.

Etiology and Pathophysiology

Many possible causes have been proposed, including hypokalemia, exposure or ingestion of plant or other toxins, nutritional muscular dystrophy, myasthenia gravis, cardiovascular disease, and unknown causes.

Diagnosis

Differential Diagnosis

• Electrolyte disturbances

Hypokalemia

Hypomagnesemia

Hypercalcemia

• Infectious or parasitic events

Encephalitozoon cuniculi

Toxoplasmosis

Neosporosis

Baylisascaris

Rabies

• Toxic plants or other toxins

Heavy metals

Botulism

Milkweeds (Asclepias spp.) contain cardiac glycosides.

Lactucarium: desiccated juice from lettuce, Lactuca spp. The wild species Lactuca virosa is poisonous, but the common or garden lettuce, Lactuca sativa, is not toxic.

• Nutritional muscular dystrophy

Vitamin E/selenium deficiency

• Myasthenia gravis

• Cardiovascular disease (see Cardiovascular Disease)

• Severe systemic disease

• Splayleg (see Splayleg)

Initial Database

• Blood biochemistry including electrolytes

• Hematologic examination including differential white blood cell count

• Serology for Encephalitozoon cuniculi, Neospora caninum, and Toxoplasma gondii

• Survey radiography to include the skull and the entire vertebral column

Advanced or Confirmatory Testing

• Heavy metal analysis (e.g., lead and zinc)

• Myelography, CT or MRI scanning of skull and vertebral column

• Cerebrospinal fluid sample collection and analysis

• Electromyography

• Myasthenia gravis diagnostic tests

Pharmacologic testing with edrophonium chloride that elicits unequivocal improvement in strength

Serologic demonstration of acetylcholine receptor or muscle-specific tyrosine kinase antibodies

Treatment

Therapeutic Goals

• To treat any identified underlying cause

• If no identified cause, to provide nutritional support, fluid therapy (see Fluid Therapy in Rabbits and Rodents, Sec. II), and other supportive care as necessary until recovery

Acute General Treatment

• Treatment of any identified underlying cause

Chelation therapy for heavy metal toxicosis (calcium EDTA 13-27 mg/kg SC q 6-12 h)

Spinal trauma treatment including stabilization, antiinflammatory medication, and surgery

Selenium and/or vitamin E for nutritional muscular dystrophy (0.1 mg Se and 5 mg vitamin E/kg IM or SC every 14 days)

• Electrolyte replacement and/or correction of electrolyte and acid-base abnormalities

Administration of oral potassium supplementation may be useful (0.5-1.0 mEq PO q 12-24 h).

• If the rabbit is able to eat and drink, provide food and water in an accessible form. This may involve supporting the head or providing assisted feeding as necessary.

• If the animal is not able to prehend food, syringe or nasoesophageal administration of food and fluids and/or parenteral fluids may be necessary.

• Ensure that bladder emptying is occurring. Manually express the bladder or catheterize the urethra if necessary.

Chronic Treatment

• Provide continued nutritional and fluid support.

• Maintain good gastrointestinal function by feeding and if necessary using gastrointestinal prokinetic drugs (cisapride 0.5 mg/kg PO q 8-24 h).

• Avoid development of pressure sores on limbs.

• Monitor for fecal soiling.

• Monitor for urine scalding due to bladder overflow or inability to move while voiding urine.

• Monitor for ocular trauma if head is immobile.

Possible Complications

• Gastrointestinal stasis

• Pressure sores

• Fecal soiling

• Urine scalding

• Flystrike

• Ocular trauma

Recommended Monitoring

• Urine output

• Fecal output

• Appetite

• Body weight

Prognosis and Outcome

• Generally good

• Recovery typically occurs in 2 to 4 days.

• Prognosis worsens if complicating factors ensue.

Pearls & Considerations

Comments

• Controversy surrounds whether FRS is an actual syndrome or is simply a catch-all descriptive term for a number of disparate entities. Although other problems can superficially resemble FRS (e.g., splayleg, severe systemic illness, encephalitozoonosis, spinal trauma, nutritional muscular dystrophy), true FRS appears to be a diagnosis arrived at by excluding other conditions with similar clinical signs. As yet, no indicator or diagnostic test can clearly identify the disorder. The exact cause is controversial, but hypokalemia appears to be implicated.

• When other serious diagnoses (e.g., spinal trauma) have been eliminated, the patient has a good to excellent prognosis for full recovery with supportive care in 2 to 4 days. However, the dramatic appearance of FRS, its similarity to spinal trauma, and lack of rapid recovery can lead owners to elect euthanasia if they are not counseled about the prognosis.

Prevention

• In most cases, no apparent precursors to FRS are noted. However, hypokalemia may contribute to development of the disease.

• Warn clients to avoid the following:

Diets containing 0.3% or less of potassium

Chronic gastrointestinal disease (because it may lead to hypokalemia)

Acute stress, fright, and hypothermia (because they may cause catecholamine-induced hypokalemia)

Client Education

Clients should be advised to seek early veterinary attention for FRS rabbits. Once more serious causes have been ruled out, advise the client that supportive care and time will usually result in a favorable outcome, as long as complicating factors are avoided.

Cross-References to Other Sections

Cardiovascular Disease

Encephalitis

Encephalitozoonosis

Fluid Therapy in Rabbits and Rodents (Section II)

Gastric Stasis (Section III)

Splayleg

Floppy Rabbit Syndrome The floppy rabbit is usually unable to stand and often splays the legs. (Photo courtesy Jörg Mayer, The University of Georgia, Athens.)

AUTHOR: RICHARD A. SAUNDERS

EDITOR: DAVID VELLA