Page 800 - Clinical Small Animal Internal Medicine

768 Section 8 Neurologic Disease

VetBooks.ir Box 70.2 Classification of hyperkinetic movement disorder types Idiosyncratic drug‐induced
Neuromuscular disorders
Myotonia
Tetany and tremor Metabolic
Hypoglycemia
Hypocalcemia Hepatic or uremic encephalopathy
Fasciculations Degenerative disease
Benign Cerebellar‐related tremor disorders
Exercise Congenital
Stress Neonatal syndromes
Toxicity Hypoplasia
Metabolic: hypercalcemia Malformation
Other causes of neuropathy Granuloprival degeneration
Myokimia Hypo‐dysmyelinogenesis
Environmental (hypothermia) Axonopathy
Postnatal syndromes
Central nervous system disorders Abiotrophy
Noncerebellar Lysosomal storage diseases
Myoclonus Acquired
Spinal Inflammatory
Proprioceptive Infectious
Epileptic Immune‐mediated
Toxicity Neoplasm
Tetanus Vascular/traumatic
Tremor Toxin
Essential Idiopathic
Toxicity

Hyperkinetic Movement Disorders exercise in the cold and maintaining a normal exercise
Myotonia routine, as drug therapy has not been shown to be
Myotonia is a sustained muscle contraction with delayed effective.
relaxation. Myotonia congenita has been reported in the
chow chow and miniature schnauzer dog breeds, and Tetanus and Tetany
seen sporadically in a number of other breeds. The dis- Tetanus is a continuous sustained extensor muscle
ease is due to a failure of normal myocyte chloride con- contraction. The cause is the tetanus toxin released by
ductance resulting in delayed muscle hyperpolarization, Clostridrium tetani bacterial infection of domestic
and therefore delayed relaxation. As an inherited auto- animals. The disease occurs when the tetanus spores
somnal recessive disease, puppies are affected from localized to an anaerobic environment, such as a necrotic
birth. Clinical signs are seen within the first few months wound, transform into the toxin‐producing form. The
of life and characterized by a stiff, “sawhorse” stance exotoxin, tetanospasm, travels from the infected site via
upon ambulation, with improvement in gait as exercise peripheral nerves to the central nervous system. The
time increases. Some dogs may suffer from dysphagia toxin prevents the release of the inhibitory neurotrans-
and respiratory problems due to contraction of the mitter glycine from interneurons in the spinal cord and
tongue and oropharyngeal muscles. Affected dogs have brain, resulting in excessive excitation of brainstem and
hypertrophied glossal and proximal appendicular mus- motor neurons.
cles that exhibit percussion dimpling upon being struck Both cats and dogs are fairly resistant to tetanus.
with a percussion hammer. When infected, they can exhibit an extreme stiffness
Electromyographic recordings demonstrate the classic progressing to extensor rigidity of all limbs, spastic facial
myotonic discharge of a high‐frequency waxing‐waning muscles and trismus within 5–10 days of infection. A
spontaneous discharge that produces a “dive‐bomber” or “grimacing” expression with the ears pulled back is usu-
revving motorcycle sound. Muscle biopsy is typically ally seen. Occasionally, localized tetanus may affect only
normal. Treatment revolves around avoiding excessive a single limb or be confined to the facial muscles. Many