Page 889 - Problem-Based Feline Medicine

40 – THE CAT WITH ANISOCORIA OR ABNORMALLY DILATED OR CONSTRICTED PUPILS 881

sensitivity to chorpyrifos, and signs of toxicity have Salivation and defecation are not life threatening and
occurred even when used according to label instruc- generally do not require atropine.
tions. Toxicity has also been reported with the flea col-
Diazepam should be avoided in these cats as it may
lars containing chlorpyrifos.
result in generalized muscle tremor, hypersalivation,
miotic pupils and vomiting similar to acute muscarinic
Clinical signs signs of organophosphate toxicosis.

Cats with organophosphate intoxication may have
acute signs including salivation, urination, defeca- NEOPLASIA*
tion and muscle weakness.
Classical signs
Postural reactions and spinal reflexes may be depressed
in some cats, but may be normal in other cats. ● Miosis with or without signs of Horner’s
syndrome.
The pupils may be bilaterally dilated and poorly
● Accompanying signs depend on the
responsive to light stimulation.
location of the tumor.
Ventroflexion of the neck and muscle tremors may ● Tumors causing miosis can occur in the
be evident. middle ear, ventral cervical area, cervical
spinal chord and brain.
● A mass may be palpated in the ventral
Diagnosis
cervical area with neoplasia of the
History of exposure to an organophosphate. vagosympathetic trunk.
Serum cholinesterase activity may lend support to the
diagnosis, but may be non-diagnostic for chronic
Pathogenesis
organophosphate toxicity. Values less than 500 IU (nor-
mal 900–1200 IU) are considered consistent with Neoplastic disease may infiltrate or compress the
organophosphate toxicity. sympathetic nerves centrally or peripherally.
Electromyographic changes are occasionally present If the middle ear is affected, the most common
and include fibrillation potentials, positive sharp waves tumors are adenocarcinoma and squamous cell car-
and bizarre high-frequency discharges. A decremental cinoma.
response to repetitive nerve stimulation may be present.
Diffuse neoplastic diseases such as lymphoma and
Beware that edrophonium (used to test for myasthe- leukemias may infiltrate the sympathetic nerves.
nia gravis) will produce an acute worsening of signs, ● Lymphoma can be associated with feline leukemia
which should be treated with atropine (0.05 mg/kg IV). virus infection.

Differential diagnosis Clinical signs
Rule out other diffuse causes of weakness. Miosis may be the primary sign or it may occur with
other signs of Horner’s syndrome. Other neurological
signs depend on the location of the tumor.
Treatment
Neoplasia involving the middle ear can result in pain
Treatment includes 2-PAM (20 mg/kg q 12 h IV) and
upon opening the mouth or during palpation around the
diphehydramine (1–2 mg/kg q 8–12 h).
ear, abnormal otic discharge and swelling around the
Atropine (0.2–0.4 mg/kg) can be given with acute tox- ear.
icity to decrease autonomic signs. Current recommen- ● Head tilt, facial paralysis and nystagmus can also be
dations suggest its use only if marked bradycardia is present when both the middle and inner ear are
present as this drug may precipitate respiratory arrest. involved.