QPlease review the clinical causes and management of abnormal movements in dogs.
QPlease review the clinical causes and management of abnormal movements in dogs.
ADogs may develop atypical gait and movement disorders that are difficultto determine the underlying cause. Movement disorders may encompass excess(hyperkinesias) or reduced (bradykinesia) movements.
Abnormal involuntary movements include muscle jerks, twitches, posturesand oscillations that have been defined as a tic, chorea, tremor, dystoniaand myoclonus. The following article describes abnormal involuntary movementsof dogs in clinical practice - Podell M: tremors, shakes and twitches: movementdisorders in small animals. Proc 20th Annual Forum ACVIM 20:362-364, 2002.
The visualization of abnormal involuntary movements should be supplementedwith a comprehensive case history. Information regarding anatomic distribution,rhythmicity, amplitude, speed of onset and offset of the movement, relationshipto posture and activity, situations that alleviate or exacerbate the movement,presence or absence during sleep, and affected littermates are essentialobservations and history to help determine the neuroanatomic localizationand potential cause.
If the abnormal movement disorder is not present at the time of the initialexamination, owners should be encouraged to videotape the events for futurereview. Many times, the initial few minutes of observation will solidifythe clinical perspective, allowing an accurate diagnostic and therapeuticcourse of action to proceed.
Excessive movement disorders
Myotonia is a sustained muscle contraction with delayed relaxation. Hereditarymyotonia occurs in the Chow Chow and is seen sporadically in Chow crossesand a number of other dog breeds. Myotonia is due to a failure of normalmyocyte chloride conductance resulting in delayed muscle hyperpolarizationand, therefore, delayed relaxation.
As an autosomal recessive disease, puppies are affected from birth. Signsinclude a stiff, "sawhorse" stance on movement, with improvementin gait as exercise time increases. Affected dogs have hypertrophied proximalappendicular muscles that exhibit percussion dimpling when being struckwith a percussion hammer.
Electromyographic recordings demonstrate the classic myotonic dischargeof a high frequency waxing-waning spontaneous discharge. Muscle biopsy isusually normal. Procainamide or quinine may be used for treatment but usuallyis unsuccessful in alleviating the myotonia. Many dogs can live a good qualitylife by avoiding excessive exercise in the cold and maintaining a normalexercise routine.
Tetanus is a continuous sustained extensor muscle contraction. Tetanusmost often occurs during the time period of shedding deciduous teeth orfrom contaminated bite wounds. The cause is the tetanus toxin released byClostridium tetani. The exotoxin, tetanospasm, travels from the infectedsite via peripheral nerves to the central nervous system. Toxin preventsthe release of the inhibitory neurotransmitter, glycine, resulting in excessiveexcitation of brain stem and motor neurons. Cats and dogs are fairly resistantto tetanus.
However, when infected, they can exhibit an extreme stiffness progressingto extensor rigidity of all limbs, spastic facial muscles and trismus within10 days of infection. Many animals are hypersensitive to external stimuli.Occasionally, localized tetanus may affect only a body region such as alimb.
Wound debridement, parenteral anaerobic antibiotic administration, musclerelaxation using acepromazine and nutritional support are used in the treatment.Complete remission of clinical signs will usually occur within several weeksto months.
Tetany is a variable and intermittent extensor muscle contraction. Tetanymay accompany both central and peripheral nervous system diseases. In dogs,tetany is most commonly seen with hypocalcemia associated eclampsia or hypoparathyroidism.
Total serum calcium is typically below 5.0 mg/dl. Affected dogs may showinability to rise, extensor muscle contractions and hyperthermia (inducedby excessive muscle contractions). Treatment includes initial muscle relaxationwith benzodiazepines, followed by calcium and vitamin D supplementation.
Myoclonus is sudden, rapid, involuntary muscle movement of short durationcaused by active muscle contractions (positive myoclonus) or pauses in muscleactivity (negative myoclonus). Reflex myoclonus to auditory stimuli occursin the Labrador Retriever breed. Spinal myoclonus arises from abnormal neuronaldischarges originating in the spinal cord. Segmental myoclonus occurs incanine distemper, producing a repetitive, myoclonic jerk motion of the oneor more limbs.
Tremors may occur either at rest or with action.
· Resting tremors describe an involuntary, rhythmic oscillationof a body part completely supported against gravity. This tremor could beseen in a leg with the animal laying down and not supporting weight.
· Action tremor occurs during voluntary contraction of skeletalmuscle and may be postural, kinetic, isometric or task-specific.
· Postural tremors describe oscillation of a body part that isvoluntarily maintained against gravity. This tremor type is uncommon insmall animals.
· Kinetic tremors describe oscillation during guided voluntarymovement. These kinetic (intentional) tremors are the most common type seenwith cerebellar disease.
· Isometric tremors and task-specific tremors are seen in primatespecies that can hold objects and initiate specific movements of the handsand arms.
· Physiologic and essential tremor syndromes may occur in olderdogs, and in particular, aging Terrier breeds. These tremors are a pureclinical syndrome characterized by progressive action tremor of pelvic limbsthat worsens with activity and excitement. Severity can range from barelyperceptible tremor to altered gait and balance problems. Signs can progressas the dog ages.
· Drug-induced tremors occur in small animals. Predictable tremorscan be seen with stimulant toxicity, such as caffeine, amphetamines andcocaine. Rhythmic involuntary movements are the most common manifestationresulting from exposure to dopamine receptor blocking agents, such as phenothiazine(e.g., acepromazine) or anti-emetic drugs (e.g., metoclopramide).
· Cerebellar-related tremors are definitely the most common causeof tremors in small animals. Congenital cerebellar diseases included hypoplasia,malformation, hypomyelinogenesis, dysmyelinogenesis, abiotrophy and lysosomalstorage disease. Acquired cerebellar diseases are inflammatory, infectious(canine distemper), immune-mediated (granulomatous meningoencephalitis andsteroid-responsive tremor syndrome), neoplasia, vascular/traumatic and toxincauses.
Cerebellar diseases are often associated with signs related to abnormalmotor activity, including any or all of the following: tremors, bilaterallysymmetric ataxia without paresis, dysmetria, vestibular signs (head tilt,nystagmus, falling), absent menace with preservation of vision and pupillarychanges.
An altered resting posture is often present with affected animals demonstratingtruncal ataxia (swaying of the body back and forth or side to side) andcompensatory broad-based stance for balance. Cerebellar tremors are associatedwith diffuse cerebellar cortical diseases. These intention tremors are characterizedby a fine head tremor that worsens with initiation of voluntary head movements.The acute onset diseases affecting the cerebellar cortex usually resultin more pronounced tremors.
Severe tremors may affect the entire body with complete loss of all muscularcoordination and failure to posture and prehend food. Ensuing hyperthermia,rhabdomyolysis and related complications from continuous muscle activityrequire that these animals be aggressively treated on an emergency basis.
Fortunately, many pure cerebellar diseases can be treated and/or compensatedfor by the animal.
Treatment of tremor disorders
Emergency treatment for acute onset tremors in the dog may significantlyreduce tremor severity. Such treatment may include diazepam at 0.5 mg/kgIV and if poor control, diazepam as continuous rate infusion (0.2-0.5 mg/kghourly IV to effect); or phenobarbital 20 mg/kg IV followed by 2 mg/kg POq12h; or propofol as continuous rate infusion (5-10 mg/kg hourly IV to effect)to stop tremors. It is also important to maintain normal body temperatureand provide intravenous fluid therapy to avoid dehydration.