Page 946 - Problem-Based Feline Medicine

938 PART 11 CAT WITH AN ABNORMAL GAIT

THIAMINE DEFICIENCY* TOXINS*

Classical signs Classical signs
● Initially, lethargy, inappetence and ataxia. ● Metronidazole toxicosis results in ataxia,
● Later signs include weakness, ventral paresis, seizures and cortical blindness.
flexion of the neck, dilated pupils, stupor ● Bromethalin toxicosis in the early stages
and coma. may also result in ataxia. Signs progress to
paresis, depression, tremors, seizures and
See main reference on page 848 for details (The Cat decerebrate posture.
With a Head Tilt, Vestibular Ataxia or Nystagmus). ● Ivermectin toxicosis has resulted in
generalized ataxia, tremor, weakness,
incoordination, and miosis in a kitten.
Pathogenesis
● Griseofulvin therapy resulted in ataxia in
Occurs in anorexic cats or cats that are fed all-fish a 12-week-old kitten.
diets containing thiaminase. ● Aminoglycosides, administered either
systemically or topically, may cause
This deficiency results in polioencephalomalacia of the
vestibular signs including ataxia.
oculomotor and vestibular nuclei, the caudal colliculus
● Chlorhexidine solution used to clean the
and the lateral geniculate body.
external ear may result in vestibular signs
including ataxia.
Clinical signs
Early non-specific signs are typically lethargy and Pathogenesis
inappetence.
Metronidazole toxicosis has been reported to result in
The earliest localizing sign is bilateral vestibular ataxia in cats.
ataxia, which appears as an abnormal broad-based ● Usually, this is associated with high doses of the
stance, loss of balance and vertigo. drug.
There is weakness and an inability or reluctance to ● As metronidazole is metabolized by the liver, how-
walk. The cat sits crouched with ventral flexion of ever, toxic serum levels can occur with appropriate
the neck. doses in animals with liver dysfunction.
Pupils are dilated and non-responsive or poorly Bromethalin toxicity results in vacuolization of the
responsive to light reflexes. nervous system, most likely due to a lack of intracellu-
lar energy.
If untreated, signs progress to semi-coma, persistent
vocalization, opisthotonos, and death.
Clinical signs
Episodes of spastic opisthotonos or ventroflexion of
the neck and generalized muscle spasm may occur Ataxia is usually the initial clinical sign of metronida-
especially when the cat is lifted or stressed. They may zole toxicity.
be interpreted as seizures, but true seizure activity ● Paresis is usually present, and seizures and corti-
rarely occurs. cal blindness may also be noted.
● These signs in association with metronidazole
administration should raise concern for toxicity.
Diagnosis
The early stages of bromethalin toxicosis may also
No antemortem diagnostic test is available.
result in ataxia.
Diagnosis is based on clinical signs and rapid ● Signs progress to paresis, depression, tremors,
response to thiamine. seizures and decerebrate posture.