Page 863 - Problem-Based Feline Medicine

39 – THE CAT WITH TREMOR OR TWITCHING 855

Tremors usually have a characteristic distance of travel
DISEASES CAUSING COURSE
(amplitude) and speed of travel (frequency). Tremors
TREMOR
can be categorized generally into those that have an
increased amplitude with a slower frequency (coarse
tremor) or a decreased amplitude with a faster fre- CEREBELLAR HYPOPLASIA**
quency (fine tremor).
Classical signs
● Signs are present from the early prenatal
WHERE?
period.
Disease of the nervous system (central and periph- ● Clinical signs usually remain unchanged or
eral) and muscle may result in involuntary tremor, may improve during life.
shaking or twitching. ● Coarse tremor that worsens when the cat
moves in a goal-oriented fashion (intention
Cerebellar disease usually results in a coarser tremor
tremor).
that worsens (increases in frequency or amplitude)
● Other signs include ataxia, hypermetria,
when the animal moves in a goal-oriented fashion
menace deficits, head tilt and nystagmus.
(intention tremor).
Other signs of cerebellar disease that accompany
cerebellar tremor include ataxia (incoordination; sway- Pathogenesis
ing from side to side), dysmetria (“goose-stepping”;
overflexing of the limbs when walking), menace Cerebellar hypoplasia results from in utero or imme-
deficits (with normal vision, palpebral, and pupillary diately postnatal infection with the panleukopenia
light reflexes), head tilt and nystagmus. virus (parvovirus).

Fine tremor (decreased amplitude and increased fre- Infection of the fetus may occur when a pregnant queen
quency) is more often associated with diffuse neuronal is vaccinated with a modified-live panleukopenia
disease or muscle weakness that result in involuntary virus vaccination.
muscle contraction.
This virus destroys the external germinal layer of the
cerebellum and prevents the formation of the granular
layer.
WHAT?
Some affected cats have a concurrent hydrocephalus
Diseases of the intracranial nervous system (primarily and hydranencephaly.
the cerebellum) resulting in tremor include storage
diseases, brain tumor, encephalitis and vascular-
based diseases.
Clinical signs
Systemic metabolic diseases altering neuronal or
Clinical signs are most apparent when the animal
muscle membrane potentials (such as hypoglycemia,
begins purposeful movement and attempts to walk.
hypocalcemia, hypokalemia) can result in tremor.
Tremor accompanying the disease usually has a slower
Diseases that decrease neuronal impulse conduction
frequency (2–6 times/second) and larger amplitude.
via abnormalities of myelin (hypomyelination) often
The tremor worsens (increases in frequency or ampli-
result in tremor.
tude), when the cat moves in a goal-oriented way (e.g.
Diseases of the nervous system that result in persist- bends down to eat), which is termed an intention
ent, fine tremor are usually diffuse (encephalitis). tremor.