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Vestibular Dysfunction in a Geriatric Dog

Mark Troxel, DVM, DACVIM (Neurology), Massachusetts Veterinary Referral Hospital, Woburn, Massachusetts

Neurology

|
August 2022
|
Peer Reviewed

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dog

A 12-year-old spayed rottweiler crossbreed is presented for emergency evaluation following sudden onset ataxia in all limbs. She is ambulatory without support but veers and stumbles to the right and occasionally falls to the right when walked on a leash. She also compulsively circles to the right when not on a leash in the examination room.

On neurologic examination, she is quiet and alert but appears disoriented and has a mild head tilt to the right. Cranial nerve examination reveals a resting horizontal nystagmus with fast phase to the left. When placed on her back, there is a positional rotary nystagmus with fast phase to the left. The remainder of the cranial nerve examination is normal. General proprioception and hopping are normal in all limbs. Patellar reflexes are normal bilaterally, and withdrawal reflexes are normal in all limbs. There is no evidence of hyperesthesia.

Neurologic examination results suggest right peripheral vestibular disorder. Differential diagnoses include idiopathic vestibular disease (ie, old dog vestibular, geriatric dog vestibular), otitis interna, hypothyroidism, aural neoplasia (eg, squamous cell carcinoma, ceruminous gland adenocarcinoma), trauma, ototoxicity, and other less common disorders. 

CBC, serum chemistry profile, and total thyroxine (tT4) results are within normal limits. Otoscopic examination is attempted, but a large amount of hair in the horizontal ear canal obstructs visualization of the tympanic membrane. 

Presumptive diagnosis is idiopathic vestibular disease, as there is no history suggestive of otitis media/interna (eg, head shaking, pawing/scratching ears or sides of face, rubbing side of head on objects), no recent use of ototoxic medications or topical cleaning agents, and no recent trauma.

Which of the following drugs would be appropriate for this patient?

Do Not Use Proceed with Caution Safe

The following represents the best responses based on drug metabolism, pharmacokinetics, species, diagnostic differentials, clinical and laboratory data, and other pertinent findings.

MAROPITANT

Correct ResponseSafe1 mg/kg SC or IV over 1-2 minutes every 24 hours or 2-8 mg/kg PO every 24 hours) is FDA-approved for use as an antiemetic in dogs and cats and is indicated for prevention and treatment of acute vomiting in dogs and cats, as well as prevention of vomiting due to motion sickness in dogs and cats ≥4 months of age.1 Although maropitant is often used to improve appetite and reduce nausea and vomiting in patients with vestibular dysfunction, there is no peer-reviewed evidence to specifically support this treatment. Maropitant is a neurokinin receptor antagonist that acts in the CNS to inhibit the binding of substance P (ie, the primary neurotransmitter involved in vomiting); peripheral and central causes of vomiting may therefore be suppressed.1

Maropitant is generally well tolerated. The most commonly reported adverse effects are pretravel vomiting and hypersalivation in patients given the higher motion sickness dose and pain or swelling at the injection site with subcutaneous administration.2,3 Other reported adverse effects include depression, lethargy, inappetence, diarrhea, anaphylaxis/anaphylactoid reactions, ataxia, and convulsions.2,3

Use of maropitant in patients with vestibular dysfunction is extra-label.

MECLIZINE

Correct ResponseSafeMeclizine (anecdotal dosage, ≈4 mg/kg PO every 24 hours; practical dosage, 12.5-50 mg/dog every 24 hours) is an H1-receptor blocker antihistamine with antiemetic and sedative properties frequently used extra-label to treat vestibular dysfunction and motion sickness; no FDA-approved veterinary products are available.4 Common adverse effects are sedation and anticholinergic effects (eg, dry eyes, dry mucous membranes, tachycardia). Paradoxical CNS stimulation has been reported.4 Nighttime administration is usually better accepted by owners.

Although meclizine is frequently recommended for treatment of vestibular dysfunction, there are no peer-reviewed studies that specifically examine use of meclizine in these patients. Meclizine typically has less sedative effect than other antihistamines (eg, diphenhydramine).

CEPHALEXIN

Correct ResponseDo Not UseCephalexin (15-30 mg/kg PO every 12 hours) is a first-generation bactericidal oral cephalosporin FDA-approved for treatment of secondary superficial bacterial pyoderma caused by Staphylococcus pseudintermedius in dogs that can also be used extra-label for treatment of other bacterial infections.5 First-generation cephalosporins generally exhibit bactericidal activity against gram-positive organisms and most anaerobes and have variable activity against gram-negative bacteria. Cephalexin has good penetration into bone and is effective against most bacteria often isolated from patients with otitis media.5-7

No data suggest antibiotics are beneficial for treatment of idiopathic vestibular disease. Antibiotics should not be given indiscriminately and should be prescribed only after infection of the middle ear is confirmed with bacterial culture and susceptibility testing (via myringotomy, if necessary). Empirical treatment may be considered if substantial evidence (ie, clinical signs, otoscopic evidence) of otitis media/interna is present. The recommended duration of antibiotic administration is 6 to 8 weeks.

Cephalexin is the author’s first antibiotic of choice in dogs suspected to have otitis media/interna because the drug is generally inexpensive, is effective for most first-time infections, and has good bone penetration.6 Patients receiving cephalexin should be rechecked at 3 to 4 weeks. If clinical signs have improved or resolved (except for head tilt, which may be permanent), cephalexin can be administered for an additional 3 to 4 weeks, as otitis media/interna can take 6 to 8 weeks to resolve. Advanced imaging (ie, MRI, CT) is recommended in patients in which clinical signs do not resolve (with the exception of head tilt).

ENROFLOXACIN

Correct ResponseDo Not UseEnrofloxacin (dogs, 5-10 mg/kg PO every 24 hours [up to 20 mg/kg PO every 24 hours for up to 30 days, according to some sources]) is a bactericidal fluoroquinolone antibiotic FDA-approved for treatment of dogs with susceptible bacterial infections.8 Enrofloxacin generally has activity against many gram-negative cocci and bacilli (eg, Pasteurella aeruginosa, Escherichia coli, Klebsiella spp, Enterobacter spp, Proteus spp) and is active against Brucella spp, Mycoplasma spp, and some Mycobacterium spp.8 Because of concern for development of bacterial resistance, enrofloxacin should ideally only be used for bacteria in which culture and susceptibility results show susceptibility to enrofloxacin.

No data suggest antibiotics are beneficial for treatment of idiopathic vestibular disease. Antibiotics should not be given indiscriminately but may be considered if clinical signs or otoscopic evidence of otitis media/interna are present. Therapeutic concentrations are attained in bone, making enrofloxacin an acceptable antibiotic for otitis media/interna, but consideration should first be given to a lower tier antibiotic (eg, cephalosporins, amoxicillin/clavulanic acid).8 Adverse effects include GI distress (eg, inappetence, vomiting, diarrhea), which may be offset by concurrent use of probiotics. There have also been rare reports of elevated liver enzymes, lethargy, depression, ataxia, and seizures.8,9

PREDNISONE/PREDNISOLONE

Correct ResponseDo Not UsePrednisone and prednisolone are glucocorticoids with anti-inflammatory activity.

Patients with otitis media/interna and concurrent otitis externa or periauricular inflammation may benefit from short-term corticosteroids or NSAIDs, but routine use of prednisone/prednisolone is not recommended in patients with idiopathic vestibular disease, as there are no data demonstrating efficacy for this condition. In addition, prednisone may mask other underlying diseases, making it difficult to obtain a diagnosis if the patient does not improve or the initial presumptive diagnosis is incorrect.

LEVOTHYROXINE

Correct ResponseDo Not UseLevothyroxine is a synthetic form of thyroxine used to treat hypothyroidism in dogs and, rarely, in cats (most often following thyroidectomy or radioiodine treatment).10 Hypothyroidism has been implicated in both peripheral and central vestibular dysfunction, but causality has not been proven, and concurrent hypothyroidism unrelated to vestibular dysfunction is possible. tT4 can be used as a screening tool but may be artificially low in patients with nonthyroidal illness (ie, euthyroid sick).

Levothyroxine is not indicated in patients with normal tT4, as hypothyroidism is unlikely the cause of vestibular dysfunction when tT4 is in the normal range. In patients with tT4 below the reference range, however, true hypothyroidism should be differentiated from euthyroid sick status via reduced free thyroxine, elevated thyroid-stimulating hormone, and possibly elevated thyroglobulin autoantibody levels prior to initiation of supplementation.

MELOXICAM

Correct ResponseDo Not UseMeloxicam is an NSAID FDA-approved for analgesia, as well as treatment of osteoarthritis and inflammatory conditions in dogs.11 No data suggest meloxicam or other NSAIDs expedite or improve the degree of recovery in patients with idiopathic vestibular disease.12

Although meloxicam has many uses and is generally safe, consideration is needed before administration to patients with potential neurologic concerns (eg, granulomatous meningoencephalomyelitis, necrotizing encephalitis, meningoencephalitis of undetermined etiology) that may need to be switched to corticosteroids because of the prolonged washout period (ie, 5-7 days) required prior to starting corticosteroids. Meloxicam can also cause GI upset and decreased appetite, further complicating recovery.

BUTORPHANOL

Correct ResponseProceed with CautionButorphanol (0.1-0.3 mg/kg IV bolus or 0.2 mg/kg IV loading dose, then 0.1-0.4 mg/kg/hour IV CRI) is an opioid agonist/antagonist used extra-label in dogs as a sedative, a preanesthetic, and an antiemetic.13 Sedation of hospitalized patients with vestibular disease may be necessary to control excessive movement (eg, flailing, rolling, compulsive circling in cage) and patient injury. Injectable (ie, intermittent bolus, CRI) butorphanol may be helpful because of its sedative and antiemetic properties. Caution is warranted when this drug is combined with other sedatives.

DIAZEPAM/MIDAZOLAM

Correct ResponseProceed with CautionDiazepam (0.2-0.5 mg/kg IV as an intermittent bolus) and midazolam (0.3-0.5 mg/kg IV as an intermittent bolus) are benzodiazepines that are schedule IV controlled substances in the United States with anticonvulsive, anxiolytic, sedative, and muscle relaxant properties, as well as possible mild appetite stimulant effects.14,15 These drugs are sometimes used because of their sedative and anxiolytic properties in hospitalized patients with vestibular dysfunction to prevent injury from excessive movement (eg, flailing, rolling, compulsive circling in cage). Benzodiazepines may cause paradoxical excitement.14,15 Caution should be used in patients with liver or kidney disease, aggressive patients, geriatric patients, and debilitated patients (eg, those with moderate to severe respiratory depression, shock, coma).14,15 Benzodiazepines may cause nystagmus in healthy patients.16

ONDANSETRON

Correct ResponseSafeOndansetron is a serotonin type 3 (5-HT3) receptor antagonist that acts on 5-HT3 receptors, peripherally on vagal nerve terminals, and in the CNS in the chemoreceptor trigger zone and is used for the prevention and treatment of vomiting.17 A recent open-label study evaluating use of ondansetron (0.5 mg/kg IV) to control nausea and vomiting in dogs with vestibular dysfunction found a significant reduction in the intensity of nausea, salivation, lip licking, restlessness, and lethargy but not in vocalization.18

CAPROMORELIN

Correct ResponseSafeCapromorelin (3 mg/kg PO every 24 hours; efficacy not tested beyond 4 days) is an FDA-approved appetite stimulant in dogs and a ghrelin-receptor agonist that stimulates growth hormone release and causes the feeling of hunger.19 Patients with vestibular dysfunction frequently have reduced appetite and nausea; capromorelin may therefore be beneficial in patients with reduced appetite not responding to antivertigo medications (eg, meclizine, maropitant). Adverse effects include GI upset (eg, hypersalivation, vomiting, diarrhea) and polydipsia.19 Caution should be used in dogs with hepatic dysfunction or renal insufficiency.19

References

For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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