Page 831 - Problem-Based Feline Medicine

37 – THE CAT WITH STUPOR OR COMA 823

INTRODUCTION Classical signs—Cont’d
● Evidence of external trauma to the head
MECHANISM? and face such as facial lacerations,
bleeding from the nose and mouth,
Stupor and coma result from diseases that primarily bruising, retinal hemorrhage or
or secondarily affect the cerebral cortex and thala- hemorrhage in the external ear canals.
mus and/or the reticular activating system of the
brain stem responsible for consciousness and wake-
fulness. Pathogenesis
Systemic (metabolic) disease may affect these areas Traumatic injury to the brain occurs most commonly
indirectly and result in stupor or coma. from automobile trauma, although gunshot wounds and
falls may also occur.

All of these disease processes result in mechanical dis-
WHERE?
ruption of intracranial tissues (primary injury) such as
Disease of the intracranial nervous system including axonal shearing.
the supratentorial structures (cerebral cortex, thalamus)
Primary injuries to the brain may initiate a number of
and the brain stem (midbrain, pons or medulla oblon-
secondary pathophysiological sequelae such as meta-
gata) may result in stupor or coma.
bolic alterations in neuronal or glial cells, impairment
of vascular supply to normal tissue (ischemia), impair-
ment of cerebrovascular autoregulation, hemorrhage
WHAT?
(intraparenchymal, intraventricular, extradural or sub-
Diseases of the intracranial nervous system resulting in dural), irritation (seizure generation), obstruction of the
coma include head trauma, brain tumor, encephalitis ventricular system; edema formation, production of
and vascular-based diseases. physiologically active products, and finally, increased
intracranial pressure (ICP).
Many of these diseases result in increased intracranial
pressure that perpetuates the clinical signs. Hemorrhage, either within or around the brain, may
result in rapid cerebral dysfunction.
These diseases are often severe.
In an experimental study of blunt craniocerebral trauma
The most common metabolic diseases producing
in cats, all had some degree of subarachnoid hemor-
stupor or coma are hypoglycemia secondary to
rhage, and many had subdural hemorrhage. Fifteen per-
insulin overdose in a diabetic cat and hepatic ence-
cent of cats had subdural hematomas that displaced the
phalopathy secondary to a congenital portosystem-
corresponding cerebral hemisphere.
atic shunt.
● Many also had cortical contusion. Intraparenchymal
hemorrhage and petechiation were common, most
DISEASES CAUSING STUPOR often in the hemisphere directly receiving the blunt
OR COMA force.
● One-fifth of the cats had tentorial herniation.
HEAD TRAUMA***
Clinical signs
Classical signs
Signs usually begin acutely after trauma.
● Acute onset of signs including stupor,
coma, paresis, gait abnormalities and Intracranial signs most commonly seen include stupor
cranial nerve deficits, especially those and coma, paresis and gait abnormalities, and cranial
involving pupillary responses. nerve deficits, especially those involving pupillary
responses.