Page 1347 - Problem-Based Feline Medicine

66 – THE CAT WITH AN ABNORMAL THIRD EYELID 1339

Differential diagnosis sue environment to support toxin production, and the
number of organisms present.
Abnormality of the third eyelid without the presence of
other signs of autonomic dysfunction would suggest Tetanus is rare in cats, because they are more resistant
localized sympathetic dysfunction such as Horner’s or to the toxin than humans and horses. This innate resist-
Haws syndrome. ance is related to the inability of the toxin to penetrate
and bind to nervous tissue, and likely accounts for the
frequency of localized signs in cats.
Treatment
Tetanus has occurred after routine surgery (such as
No definitive treatment is available. Prognosis is gen-
ovariohysterectomy), fetal death during pregnancy, and
erally guarded to poor, however supportive treatment is
trauma.
reported to be variably effective.
Tetanus may occur in young cats associated with a gum
wound secondary to losing a deciduous tooth.
TETANUS

Classical signs Clinical signs

● Bilateral third eyelid prominence. Signs of tetanus may be localized or generalized, or
● Contraction of facial muscles, increased may begin with localized signs and progressively
tone in muscles of mastication (“lockjaw”). involve more muscle groups over a week or more, and
● Stiffness of one or more limbs which become generalized. Generalization is more likely if
worsens with stimulation. there is inadequate wound management, or inadequate
antibiotic therapy.
Diagnosis may be difficult in the early stages of the
Pathogenesis disease when characteristic signs of generalized tetanus
are absent.
Signs of tetanus result from the toxin produced by
Clostridium tetani, a spore-forming, Gram-positive Classical signs of generalized tetanus include bilateral
rod. C. tetani is found in the soil, and also occurs as third eyelid prominence in association with contrac-
part of the normal gastrointestinal tract flora of some tion of the facial muscles giving the appearance of
animals. a“sardonic smile”, and increased tone in the muscles
of mastication (“lockjaw”). The cat may have a “star-
Spores of the Clostridium tetani bacillus enter the body
tled” appearance.
commonly via surface wounds. The toxin, tetanospas-
min, is produced during cell growth, sporulation and Focal tetanus results in stiffness of the muscles in
lysis, if there is a suitable anaerobic environment for closest proximity to the wound, and is often evident
the bacteria. The toxin migrates along nerve axons as stiffness of one or two limbs.
from a local wound, to sites of action in the central
In many cats, a neglected wound with necrotic tissue
nervous system, where it initially binds to presynaptic
is found, suggesting a site for toxin production.
inhibitory motor nerve endings. The effect of the toxin
is to block the release of inhibitory neurotransmitters Tetanus may be associated with infection of the female
(glycine and gamma-amino butyric acid) across the reproductive tract, and may produce local signs in the
synaptic cleft. This results in uninhibited muscle con- pelvic limbs.
traction.
The history of a penetrating or neglected wound, and
The incubation period for signs to develop varies from the presence of persistent involuntary muscle rig-
3–21 days after an injury, depending on the proxim- idity in a mentally alert cat is highly suggestive of
ity of the injury to the CNS, the ability of the local tis- tetanus.