EPILEPSY IN DOGS AND ITS MANAGEMENT
R. C. Patra and S. K. Parida
Department of Medicine, College of Veterinary Science and Animal Husbandry, Orissa University of Agriculture and Technology, Bhubaneswar – 751 003
Epilepsy refers to series of frequent seizures or convulsion and does not identify a disease, but rather describes a clinical sign. It is associated with paroxysmal self-limiting functional cerebral disturbance characterized by abnormal electrical activity of the brain leading to overt clinical signs of random muscle movement and sudden loss of consciousness. Each attack of epilepsy in dogs, like in human beings, can have seizures and seizure disorders. Basically, brain cells use electrical and chemical signals to communicate, which can either activate or shut off another neuron. Seizures are thought to be caused when there is an imbalance of excitatory and inhibitory signals in the brain. The malfunctioning of brain results in firing a barrage of electrical signals through the nervous system and is manifested by convulsion either in a specific body part, or more commonly, many areas at once. Many a times, the word epilepsy is used interchangeably with seizures, convulsions, attacks or fits. It is one of the top three concerns among more than 80 health issues in dogs, according to recent survey conducted by American Kennel Club. It affects anywhere from 0.5 to 5.7 percent of canine population.
A seizure presents a terrifying spectacle- especially because the dog seems to have no awareness of the surrounding. Most seizures are not life threatening and will end in a matter of seconds, although it may seem like hours. However, the dog with seizures may requires immediate and critical veterinary intervention if the seizures continues to persist for more than 30 minutes without relapse. The dog may paddle his feet or become rigid and violently thrash about.
There are many possible reasons why a dog might have a seizure. Anything capable of changing the nerve function within the brain may produce a seizure. Known causes of seizures include infectious diseases (distemper), metabolic diseases (hypoglycemia), toxic substances, neoplasia (tumors), and certain bacterial and fungal organisms. A metabolic disorder, such as hypoglycemia (low blood sugar), is often the cause in toy breeds. Hypocalcemia (low calcium) can cause seizures in bitches, nursing puppies. Puppies with distemper are also prone to seizures. Sometimes, a dog can develop seizures after an accident or a blow to the head. A post traumatic scar may develop and result in seizures. Encephalitis, a brain infection that causes inflammation, can lead to convulsions. Brain tumors, more often found in older dogs, can cause malfunctioning in the nervous system inducing seizures. Other causes of seizures include heat stroke, congenital malformation of the brain, and ingestion of toxic chemicals.
The epilepsy in dog is broadly classified into two types.
- Idiopathic or Primary Epilepsy- No known cause for the condition and it is assumed to be an inherited condition
- Secondary Epilepsy – This diagnosis is used when a specific cause for the seizures can be A veterinarian will normally run a variety of tests to rule out possible physiological or toxic causes before diagnosing the dog as having the idiopathic epilepsy.In a retrospective study, Varshney and Ali (2000) observed that the problem was more common in adults and males than younger dogs and females. Extra-cranial causes noted in such problem in dogs included strychnine toxicosis, hypocalcemia, and hypoglycemia by Babesia gibsoni, drug intoxication, and intracranial causes were viral encephalitis, canine distemper etc. Besides, there is a long list of potential causes. A diagnosis of idiopathic epilepsy is generally made when all other seizure-inducing factors have been ruled out.Idiopathic epilepsy is the most common cause of recurrent seizures in dogs and the age of onset is usually between 1 and 3 years. Some practitioners use a broader range, from 6 months to 5 years. The published prevalence ranges from between 0.5 to 4.1 percent and males are more affected than females (Jaggy et al., 1998). In 125 cases of confirmed idiopathic epilepsy, seizures were recorded in dogs of all the age groups and the peak age for the onset of first seizure was between one and five years. On the other hand epilepsy is called acquired or secondary when it occurs in previously healthy dogs whose brain has become seizure-prone for some specific reason.
Breed predisposition and inheritance:
The genetic basis of idiopathic epilepsy in dogs has received considerable attention in recent years. Certain breeds seem particularly prone to developing it, suggesting the role of a genetic factor. Among the breeds most commonly affected are Beagles, Dachshunds, Dalmatians, German shepherd dogs, Keeshonds, Boxers, Cocker and Springer spaniels, Collies, Golden and Labrador retrievers, miniature Schnauzers, Poodles, St.Bernards, Siberian Huskies, and Wire- haired terriers. Following recognition by the Swiss Labrador retriever club that seizures in this breed were becoming a matter of increasing concern, a study was conducted involving 799 pedigree certificates from a population of healthy and epileptic dogs (55) from 11 generations (Jaggy et al., 1998). The study revealed that males were no more affected than females. The increased manifestation of seizures in some subpopulation and the repeated occurrence in different families of the same sire suggested that there was genetic basis for the condition in the breed. The results also supported the hypothesis of a polygenic, recessive mode of inheritance that requires to be defined through objective test-mating programme.
Possible causes of seizures in dogs of different age group
- Under 8 months- Developmental Disorders, Encephalitis or Meningitis, Trauma, Portacaval shunt, Hypoglycemia, Toxins, Intestinal parasites, Idiopathic Epilepsy (rare)
- 8 months to 5 years- Idiopathic Epilepsy (most common), Developmental disorders, Trauma, Encephalitis or meningitis, Acquired hydrocephalus, Neoplasia (tumor), Portacaval shunt, Hypoglycemia, Electrolyte disturbances, Hypothyroidism, Toxins
- Over 5 years- Neoplasia (tumor), Degenerative disorders, Vascular disorders, Hypoxia (lack of oxygen in body tissues), Hypoglycemia, Idiopathic Epilepsy, Trauma, Encephalitis or meningitis, Acquired hydrocephalus, Serious Liver disease, Hypocalcemia, Electrolyte disturbances, Hypothyroidism
Pathophysiology
A seizure is a transitory disturbance of brain function. It has a sudden onset, ceases spontaneously, and tends to recur. A seizure results from a sudden and uncontrolled electric discharge of neurons in the cerebral cortex of the brain due to paroxysmal depolarizing shift of neurons. Neurons can spontaneously discharge for several reasons, including decreased inhibitory neurotransmitter activity, increased excitatory neurotransmitter activity or combination of both. Neurotransmitter activity can be altered by a change in the cell membrane or the internal cell metabolism. At the beginning of a seizure, only a few highly unstable neurons may spontaneously discharge. This initial discharge can cause surrounding neurons or neurons in the opposite brain hemisphere to discharge as well and spread the seizure activity by a processes referred to as kindling and mirroring, respectively. Spontaneous discharge can be triggered by almost any alteration in a neuron’s environment. Neuronal changes influence the threshold for depolarization that causes seizure activity. High frequency and low amplitude paroxysmal discharge with either a focal or generalized distribution have been observed in majority of cases of idiopathic epilepsy, and electroencephalographic features during interictal period reamin consistent, despite anaesthesia (Jaggy and Bernardini, 1998)
There are many evidences justifying the role of immediate early gene c-fos in physiological and pharmacological properties in the central nervous system. To elucidate the role of c-fos in seizure induction, male wistar rats were pretreated with antisense c-fos and nonsense c-fos oligodeoxynucleotides 12h prior to intraperitoneal administration kainic acid that induces neuronal discharges. Antisense c-fos unlike nonsense oligodeoxynucleotides inhibited the number of wet dog shakes and the appearance of limbic motor seizures. The anticonvulsant effects were associated with reduction of both Fos and NGFI-A immunoreactivity and neuroprotection in the hippocampus, thalamus and primary olfactory cortex-amygdaloid region suggesting that c-fos plays a role in the generation of kainic acid-induced limbic seizures and neuronal death (Panegyres and Hughes, 1997). Astrocytes support the neuronal function and helps in altering the seizure susceptibility through ATP production and aconitase activity. Inhibition of aconitase activity in astrocytes lowers the doses of both kainic acid and pilocarpine that is required to induce behavioural seizure (Lian and Stringer, 2004)
Clinical manifestation
Most seizures occur in three stages, each characterized by specific clinical signs. The first part of a seizure, called the aura. This often goes unnoticed but the dog shows changes in the behaviour signaling an impending seizure, and is clinically characterized by apprehension, restlessness, nervousness, and salivation. The period of aura lasts from a few seconds to few days. The aura is followed by the actual seizure, called the ictus. Although it seldom lasts for more than one minute, it can be a very disturbing event to the owner. During the seizure, the animal usually collapses onto its side and experiences a series of violent muscle contractions associated with paddling of the feet and rigidity of the body. Loss of consciousness, excessive salivation, and involuntary urination and defecation may also occur in more severe seizures. The period immediately following the seizure is known as the postictal phase. It usually lasts less than one hour but may last as long as one or two days. The animal may show signs of confusion, disorientation, restlessness, and temporary blindness. In cases of repeated seizures, the inter-ictal period denotes the interval between seizures.
Some animals are normal during this period and others are not, depending on the cause of the seizures.
Behavioural changes associated with seizures include loss of memory, lack of consciousness, altered muscle tone or movement, alteration in visual, auditory, or olfactory hallucinations and salivation, urination, defecation, or other autonomic nervous system disruptions.
Thus, depending on severity of the seizure and the duration of different stages, it is termed as Grand mal, when the seizure is severe. The term petit mal refers to a generalized seizure with a specific EEG pattern. However, the above two terminologies are no more used. A series of seizures within a short period of time, with the dog regaining consciousness between seizures is termed as Cluster seizures. Status epilepticus refers to rapidly repeating seizures with no period of consciousness between them. Seizures are classified as either partial or generalized. In the former case, neurons discharge in a specific area. In case of generalized seizures (also referred to as tonic-clonic seizures) involve an animal’s entire body. During the first (i.e. tonic) phase, which usually lasts between 10 and 30 seconds, an animal falls to the ground, loses consciousness, and rigidly extends to legs; it may also stop breathing or shake. In the second (i.e. clonic) phase, the animal’s legs make running or paddling, its mouth makes chewing motions, and it may continue to shake. In addition, an animal may urinate, defecate, have dilated pupils, salivate excessively, vocalize, or vomit during either phase. A seizure may alternate between tonic and clonic phases once or repeatedly for the duration of the seizure. The entire seizure usually lasts between 1 and 2 minutes.
Thus, depending on the clinical manifestations, seizures are classified as follows.
Generalized Seizure: Tonic-colonic (Grand Mal or Mild)
In the grand mal seizure, the tonic phase occurs as the animal falls, loss consciousness, and extends its limbs rigidly. Respiration also stops (apnea). This phase usually lasts 10-30 seconds before the clonic phase begins. Clonic movements include paddling of the limbs and/or chewing. Other signs that appear during the tonic or clonic phase are dilation of the pupils, salivation, urination, and defecation. The mild seizure involves little or no paddling or extension of limbs, and usually no loss of consciousness. Generalized seizures are usually associated with primary epilepsy.
Petit Mal Seizure (aka Absence Seizure)
Depending on the authority quoted, petit mals are described as either very rare or usually unrecognized in animals. Signs are brief (seconds) duration of unconsciousness, loss of muscle tone, blank stare, and possibly upward rotation of eyes. According to one authority (Kay), the term petit mal is misused by veterinarians and should only be accorded to cases manifesting very specific clinical signs and EEG abnormalities.
Partial Seizures
Movements are restricted to one area of the body, such as muscle jerking, movement of one limb, turning the head or bending the trunk to one side, or facial twitches. A partial seizure can progress to (and be mistaken for) a generalized tonic-clonic seizure, but the difference can be established by noting whether or not a seizure starts with one specific area of the body. Partial seizures are usually associated with secondary epilepsy.
Complex Partial Seizure (aka Psychomotor or Behavioral)
It is associated with bizarre or complex behaviors that are repeated during each seizure. People with complex partial seizures may experience distortions of thought, perception or emotion (usually fear), sometimes with unusual visual, olfactory, auditory and gustatory sensations. If dogs experience the same things, it may manifest lip-smacking, chewing, fly-biting, aggression, vocalization, hysterical running, cowering or hiding. Vomiting, diarrhea, abdominal distress, salivation, blindness, unusualthirst or appetite, and flank biting are other signs. There is an obvious lack of awareness though usually not lack of consciousness. Abnormal behaviors may last minutes or hours and can be followed by a generalized seizure. Complex partial seizures are usually associated with secondary epilepsy.
Cluster Seizures
Cluster seizures refer to multiple seizures within a short period of time with only brief periods of consciousness.
Status epilepticus
Status epilepticus can occur as one continuous seizure lasting 30 minutes or more, or a series of multiple seizures in a short time with no periods of normal consciousness. It can be difficult to tell – emergencies. Most status patients usually suffer from generalized tonic-colonic seizures. Though status epilepticus can occur with either primary or secondary epilepsy, it may also suddenly arise in dogs with no previous history of seizures (traumatic brain injury, toxins, or disease).
Seizure threshold
It has been reported that each animal inherits a “genetically determined predisposition to seizures”, and seizures occur when this threshold is exceeded. In other words, a physical condition, which may cause seizures in a low-threshold animal, may not cause seizures in a “normal” animal. The seizure threshold is apparently exceptionally low in animals that suffer from idiopathic (primary) epilepsy. An animal’s threshold can also be altered by other means. Certain types of tranquilizers (e.g. acepromazine) may induce seizures in animal with a low threshold. The medical condition of alkalosis is reported to decrease the threshold.
Management of seizures
There is no cure or standard protocol for treating idiopathic epilepsy. However, seizures can be controlled with anticonvulsant drugs. The purpose of the treatment is to decrease the frequency, duration and severity of the seizure. Treatment is individualized for each animal based on its history and physical examination. No single drug is always effective; several drugs or a combination of drugs may have to be tried before a successful treatment is found. Also, it could take several weeks to establish a therapeutic dosage that works for an individual dog. This may indicate a need to change medication or alter the dose. It might be necessary to medicate the dog several times daily for the rest of its life and the medication schedule must be closely followed. Variance from the schedule may potentiate a seizure or series of seizures.
The etiological factors in cases of secondary epilepsy should be given due to attention and therapy should be instituted to minimize or eliminate the problem that gives rise to seizure. However, in such cases anticonvulsants are to be given to suppress the motor activities. Blood tests have to be performed to rule out/ identify metabolic disorders, toxic chemicals in the dog’s system, infection or inflammation. A fasting blood glucose test can reveal certain metabolic causes for seizures. A neurological examination can point towards an underlying disease of the central nervous system, which may be confirmed by tests done on the dog’s cerebrospinal fluid. This fluid is collected from dogs under general anesthesia. More advanced tests, such as electroencephalograms (EEG) and brain scans are rarely carried out due to lack of facility and well trained personnel with sound knowledge on interpreting the findings. They are performed only when a dog’s epilepsy proves to be difficult to treat, and they are generally available only at well-equipped animal hospitals.
The two most popular medications for long term seizure control are phenobarbital and potassium bromide. Each is an effective anticonvulsant, which can be used alone or in combination. However, 10 to 50% of the dogs having seizures are found to refractory to Phenobarbital sodium (Podell, 1995). Bromide is a halide anticonvulsant that offers an effective alternative to Phenobarbital and other barbiturates for treatment of epilepsy in dogs (Schwartz et al, 1991). The use of potassium bromide (KBr) as an anticonvulsant in dogs with severe signs (seizures) has been very helpful, particularly in cluster seizures. The drug is not metabolized by the liver and has fewer drug interactions than Phenobarbital. Primidone, once more frequently prescribed, is no longer recommended, as it seems to cause greater liver toxicity than Phenobarbital. Its administration needs to be carefully monitored by veterinarians to insure that a therapeutic dose has been achieved. Trepanier et al (1998) recorded 50% reduction in seizure frequency in 72% of epileptic dogs following initiation of treatment with potassium bromide. Long term control of psychomotor seizures can be achieved with carbamazepine despite its serum low to un-measurable concentration. This has been attributed to the effects of its metabolite on seizure control; thus serum concentration of the drug is not the useful guide to clinical efficacy in epileptic dog (Holland, 1988).
Failure of treatment
There are many reasons why medical treatments can fail. The biggest reason is the owner’s lack of proper administration of the prescribed drug. The progression of an underlying disease (such as brain tumor) may resist treatment. Also, gastrointestinal disorders can affect drug absorption, and tranquilizers may stimulate seizures. Drug interactions can occur and adversely affect the level of anticonvulsant drug in the dog’s system. And it just might be that a particular drug may not work for that animal.
Alternative therapies
These range from acupuncture to vitamin therapy. Traditional acupuncture therapy for epileptic dogs involves the placement of needles in up to 10 areas of the body. Needles can be left in place from 20 minutes to over a month. Acupuncture is not usually considered a substitute for drug therapy, but is used in conjunction with them. Of 5 dogs with intractable epilepsy, followed after gold bead implants in acupuncture points, 2 dogs relapsed after five months. Two reports of epileptic dogs given acupuncture in the ear (Shen-men point) are more positive. One dog enjoyed a six-fold increase in time between seizures; the other was seizure-free for 200 days after a previous history of monthly seizures.
Some forms of epilepsy respond to supplementation of vitamin B6, magnesium, and manganese. It has long been known that a deficiency of vitamin B6 or any interference with its function can cause seizures in any mammalian species including man and dog.
Control and Awareness of pet owners
While epilepsy can’t be cured, it can be controlled. It is important to brief the dog owner that it is a chronic condition and needs lifelong management and the dog can have a good life even if it has epilepsy. Most seizures are not life threatening and will end in a matter of seconds, although it may seem like hours. The foremost important tips the dog owner should be advised is to remain calm and to remove objects that the dog might knock into and to place a towel or mat under the dog’s head if it is banging against a hard floor.
There is little danger of the dog swallowing his tongue. Of greater concern is a dog aspirating vomit if it throws up during an attack, so owners should quickly move a dog away from anything it could inhale. The owner should be advised to sit with dog and soothe it during the period of recovery. It may sometimes take a dog several minutes or longer to recover from a seizure, and comforting presence of the dog owner really matters.
References
- Holland, T. (1988). Successful long term treatment of a dog with psychomotor seizures using carbamazepine. Aust. Vet J. 65: 389-392
- Jaggy, and Bernardini, M. (1998). Idiopathic epilepsy in 125 dogs: A long term study. Clinical and electroencephalographic findings. J. Small Anim Practice 39: 23-29
- Jaggy, , Faissler, D., Gaillard, C., Srenk, P. and Graber, H. (1998). Journal of Small Anim. Practice 39: 275-280
- Lian, Y. and Stringer, J. L. (2004) Inhibition of aconitase in astrocytes increases the sensitivity to chemical convulsants. Epilepsy Res. 60: 41-52
- Panegyres, K. and Hughes, J. (1997). The anticonvulsant properties of antisense c-fos oligodeoxynucleotides in kainic acid-induced seizures. J. Neurol. Sci. 153: 12-19
- Podell, (1995). Phenobarbital: the good, the bad and the ugly, In Proceeding of 13th Annu Forum of ACVIM, 435-438
- Schwartz-Porsche, and Jurgens, U. (1993). Effectiveness of bromide in therapy resistant epilepsy of dogs. Tierarztl Pras 19: 395-401
- Trepanier, A., Schoick, A. V., Schwark, W.S. and Carrillo, J. (1998). JAVMA 213: 1449- 53
- Varshney, J. and Ali, S. L. (2000). Clinico-epidemiological and therapeutic studies in canine seizure. Indian J. Vet Med. 20: 72-75
- https://www.pashudhanpraharee.com/epilepsy-in-dogs-diagnosis-treatment/
- https://vetspecialists.co.uk/fact-sheets-post/treatment-for-epilepsy-in-dogs-fact-sheet/#:~:text=The%20first%20line%20treatment%20in,Diazepam%20(Valium)%20or%20Gabapentin.
