Page 801 - Clinical Small Animal Internal Medicine

70 Seizures and Movement Disorders 769

animals are hypersensitive to external stimuli. The diag- obese animals. One can usually detect a fine “rippling”
VetBooks.ir nosis is based predominantly on a history of recent movement of the muscle as a sign of fasciculation.
The differential diagnoses of muscle fasciculations
wounds and clinical signs. Initial treatment consists of
aggressive wound debridement, parenteral penicillin
or metronidazole treatment, muscle relaxant therapy range from the benign to the more severe neuromuscu-
lar disease. Benign, or contraction, fasciculations can be
(diazepam constant‐rate infusion at 0.3 mg/kg/h or seen after strenuous exercise and possibly in very tense
pentobarbital 3–10 mg/kg IV to effect) and nutritional animals. Other transient muscle fasciculations can be
support. Tetanus antitoxin (100–1000 IU/kg IV) has associated with hypercalemia, hypomagnesemia, and
been reported to reduce the duration of clinical effects. certain toxic drug reactions, to include theophylline,
A test dose of 0.2 mL SC should be given first to test for terbutaline, caffeine and methylxanthine (chocolate tox-
anaphylactic reaction. Careful attention should be given icity), and anticholinesterase agents (i.e., pyridostigmine
to hydration and nutritional support, as the trismus can and neostigmine used for the treatment of myasthenia
prevent adequate fluid and food intake. Complete remis- gravis). Fasciculations associated with neuromuscular
sion of clinical signs will usually occur within several disease are most likely to be present after the onset of
weeks to months. clinical signs of weakness. Degenerative feline and canine
Tetany is a variable and intermittent extensor muscle motor unit disease and more advanced cases of distal
contraction. It may accompany both central and periph- axonopathy in the dog are conditions that are more likely
eral nervous system diseases. In dogs, tetany is most to be associated with muscle fasciculations.
commonly seen with hypocalcemia‐associated parturi- Myokimia is a pattern of abnormal muscle contraction
tion or hypoparathyroidism. Total calcium is typically that produces a “rippling” or “writhing” appearance of
below 7.0 mg/dL. Dogs will often suffer from an inability the area involved. The change is the result of spontane-
to rise, extensor muscle contractions, and hyperthermia ous discharges of large motor units. Myokimia is an indi-
(from muscle contractions). Secondary hypoglycemia cation of neuronal disease followed by sprouting of the
may also be seen due to the excessive muscle move- motor unit territory in response to the denervation.
ments. Treatment is focused on initial muscle relaxation Myokimia or myokimia‐like syndrome has been
with benzodiazepines, followed by calcium and vitamin described in Jack Russell terriers and is associated with
D supplementation. hyperthermia and collapse.

Myoclonus Tremor Syndromes
Myoclonus is defined as a sudden, rapid, involuntary A number of tremor syndromes have been described in
muscle movement of short duration caused by active affected humans that are also seen in small animals.
muscle contractions (positive myoclonus) or pauses in Tremor is defined as a rhythmic oscillation of a body part
muscle activity (negative myoclonus). Classification can and classified according to its anatomic distribution, fre-
be by clinical presentation, site of origin, or etiology. quency (tremors/s, or Hertz) amplitude (fine or coarse
Reflex myoclonus to auditory stimuli has been reported with increasing severity), presence at rest, standing (pos-
in the retriever dog breeds. Spinal myoclonus arises from ture), or movement or performance of specific tasks
abnormal neuronal discharges originating in the spinal (intention), The degree of tremor (amplitude) is often
cord and is of two main types: segmental and propriospi- variable, and can be exacerbated with emotional (anxiety)
nal. Segmental myoclonus can occur in canine distem- and physical activity and stimulant drugs (e.g., caffeine).
per‐infected dogs, producing a repetitive, myoclonic jerk The two main types of tremor are known to occur either
motion of one or more limbs, even during sleep. Epileptic at rest or with action. Rest tremor describes an involun-
and drug‐induced myoclonus in dogs are examples of an tary, rhythmic oscillation of a body part completely sup-
etiologic classification. ported against gravity. This tremor could be seen in a leg
with the animal lying down and not supporting weight.
Fasciculations and Myokimia Action tremor occurs during voluntary contraction of
Muscle fasciculations are spontaneous contractions of skeletal muscle and is classified as postural, kinetic, iso-
muscle fibers within a motor unit and arise from ectopic metric or task‐specific. Kinetic tremor describes oscilla-
electrical activity in the distal axons. Fasciculations typi- tion during guided voluntary movement, also known as
cally are the manifestation of irritability of the neuronal an intentional tremor, and is the most common type seen
cell body (motor neuron) or its accompanying axons. As with cerebellar disease in small animals.
such, they are most often associated with motor neuron
disease and peripheral nerve disorders. Fasciculations can Essential Tremors
be more readily observed in the distal appendicular mus- Physiologic and essential tremor syndromes are the
cles and the tongue but can be difficult to detect in more most common in people and can occur in older dogs, in