Page 802 - Clinical Small Animal Internal Medicine

770 Section 8 Neurologic Disease

particular aging terrier breeds. In dogs, it is a pure clini- diseases affecting the cerebellar cortex usually result in
VetBooks.ir cal syndrome characterized by progressive action tremor more pronounced tremor disturbances. Severe action‐
related tremors may affect the entire body, with com-
of pelvic limbs, starting with posture that worsens with
activity and excitement. Severity can range from barely
posture and prehend food. Ensuing hyperthermia, rhab-
perceptible tremor to altered gait and balance problems. plete loss of all muscular coordination, and failure to
Signs can progress as the dog ages. domyolysis, and related complications from continuous
muscle activity require that these patients be aggressively
Tremor Associated with Neuromuscular Disease treated on an emergency basis (see later). Fortunately,
Tremor attributed to weakness is almost always associ- many “pure” cerebellar diseases can be treated and/or
ated with underlying nerve disease. Most likely, this type compensated for by the patient.
of tremor is an exaggeration of the normal physiologic Cerebellar syndromes associated with tremor can be
tremor that results from the synchronized discharge of divided into congenital and acquired diseases (see
enlarged motor units in patients with a reduced number Box 70.2). Congenital neonatal syndromes represent dis-
of surviving motor neurons. Dogs with advanced periph- eases of the newborn animal in which the clinical signs
eral neuropathies can present with this type of tremor in are present from birth and nonprogressive. In contrast,
the pelvic limbs. The tremor is exaggerated after exercise the clinical signs of congenital postnatal diseases begin
and while standing. Other conditions that directly affect in the pediatric animal after birth and are slowly progres-
nerve function with this type of tremor include compres- sive. Acquired cerebellar diseases can be either acute or
sive neuropathy from lumbosacral disk disease or steno- chronic in onset, with rapid progression most commonly
sis, nerve sheath tumors, and other mass effects or seen with inflammatory diseases and toxic exposures
entrapment syndromes involving the nerve. (e.g., mycotoxins, metaldehyde, macadamia nuts).

Drug‐Induced Tremors Diagnosis
Drug‐induced tremor has been reported in the cat and
dog. Predictable tremor can be seen with stimulant tox- The diagnostic approach to an animal with AIMs starts
icity (e.g., caffeine, amphetamines, cocaine, etc.). Other with an evaluation of whether the movement disorder is
potential drugs that have induced tremor in humans hyperknetic, hypokinetic or paroxysmal (Figure 70.2).
include valproic acid, amiodarone, procainamide, and The next step is to determine if the animal exhibits any
lithium. Tardive dyskinesia represents a wide variety of signs of tremor of the head, neck or other areas of the
involuntary movements in humans, including chorea, body. Animals without tremor should then be evaluated
dystonia, akathisia, myoclonus, tremor, and stereotypies. for signs of excessive rigidity or stiffness. Constant exten-
Stereotypy, or rhythmic involuntary movements, is the sor muscle rigidity is more likely to be a sign of tetanus,
most common manifestation resulting from exposure to while variable extensor muscle rigidity is associated with
dopamine receptor‐blocking agents, such as phenothia- tetany. An initial metabolic evaluation of a complete
zine (e.g., acepromazine) or antiemetic drugs (e.g., blood count, serum chemistry panel, ionized calcium,
metoclopramide). and creatine kinase should be performed. Tetanus is
diagnosed predominantly on clinical signs and history,
Cerebellar‐Related Tremors while tetany is diagnosed typically on the presence of
By far the most common cause of tremor in small ani- hypocalcemia or other metabolic disorder.
mals is cerebellar syndromes and disease. Cerebellar dis- If no extensor muscle rigidity is detected, then signs of
eases are often associated with a conglomeration of signs abnormal muscle movement of myotonia, fasciculation,
related to abnormal motor activity to include any or all of or myokimia should be suspected. These signs are all
the following: tremors, bilaterally symmetric ataxia with- indicators of underlying neuromuscular disease, and as
out paresis, dysmetria, vestibular signs (head tilt, nystag- such merit further specific diagnostic testing for either
mus, falling), absent menace with preservation of vision, peripheral neuropathy or myopathy. Again, an initial
and pupillary changes. An altered resting posture is often metabolic evaluation of a complete blood count, serum
present, with affected animals demonstrating truncal chemistry panel, ionized calcium, and creatine kinase
ataxia (swaying of the body back and forth or side to side) should be performed. The next level of testing would be
and compensatory broad‐based stance for balance, electrodiagnostic evaluation with electromyography and
known at titubation (cerebellar postural tremor). nerve conduction testing. Electromyography (EMG)
Cerebellar tremors are associated with diffuse cerebellar tests the stability of the muscle membrane.
cortical diseases. These intention tremors are character- If tremor is present as part of the history or clinical
ized by a fine head tremor that worsens with initiation examination, then the next step is to determine if any
of voluntary head movements. The more acute‐onset paresis is present. Care must be taken not to confuse