Take a practical approach to the management of seizures in dogs
Seizures are the most common neurological problem encountered in small animal practice. It has been estimated that up to 5 percent of dogs in the general population will seizure during their lifetime. The management of seizure disorders can be quite challenging; there are numerous causes and diverse manifestations of seizures, and response to treatment is often variable. However, by adopting a systematic approach to the evaluation of seizures, the practitioner can manage even the most difficult cases more effectively.
• Step 1: Confirm that the episodes are seizures. Seizures are episodic events and are frequently not observed by the practitioner. Because of this, it is necessary to obtain an accurate description of the episode from the owner to determine whether or not a seizure disorder is considered likely. Disorders that can be confused with seizures include syncope, narcolepsy/cataplexy, transient vestibular dysfunction and behavioral disorders. Narcolepsy/cataplexy, vestibular dysfunction and behavioral disorders typically are not associated with the alterations in consciousness seen with most seizures. Syncope does cause loss of consciousness, but the episodes manifest with muscle flaccidity rather than rigidity or movement that is typical of seizures, and animals are usually normal immediately after the syncopal event in contrast to the abnormalities frequently observed in a postictal period. If the episode proves difficult to characterize based on the description alone, it can be helpful to have the owner videotape an episode for review.
• Step 2: Characterize the seizure type. Generalized seizures typically involve alterations in consciousness with rhythmic involuntary motor activity of the limbs and face, and variable degrees of salivation, urination and defecation. In contrast, partial seizures manifest as isolated head turning, licking, jaw snapping, movement of a single limb or behavioral changes. It has long been accepted that primary generalized seizures are the most frequently recognized type of seizure in dogs. However, some recent studies suggest that partial onset seizures may be more common than previously believed. Partial seizures are caused by an underlying abnormality in a focal area of the brain. Accordingly, characterizing the seizure type will help in the development of a differential diagnosis list and the diagnostic plan.•Step 3: Obtain a thorough history. Historical information can be useful in formulating a differential diagnosis. Questions should be asked regarding the age at the onset of seizures, any events that seem to precipitate the seizures, any past history of trauma (which usually has to be severe enough to render the dog unconscious), potential exposure to toxins, vaccination history, any family history of seizures and any past illnesses.
•Step 4: Perform a complete physical and neurological examination. The majority of dogs that are evaluated for seizures are normal between episodes. Nonetheless, it is imperative to perform a complete examination to look for evidence of concurrent disease or subtle neurological signs that might be present. With respect to the latter, animals should be evaluated for any change in mentation or behavior, visual deficits, gait abnormalities or postural reaction deficits. In addition, a fundoscopic examination should be performed to evaluate for the presence of retinal lesions, as inflammatory conditions affecting the central nervous system frequently also involve the retina.
•Step 5: Formulate a list of differentials and a diagnostic plan. The causes of seizures can be divided into extracranial and intracranial categories. Extracranial causes include metabolic or toxic disturbances that secondarily effect brain function, such as hepatic disease, renal disease, electrolyte disturbances, hypoglycemia, polycythemia and toxicity due to exposure to various compounds including lead and other heavy metals, organophosphates, strychnine, metaldehyde and ethylene glycol. Intracranial causes refer to structural or functional abnormalities of the brain that incite seizures. This category includes anomalous disorders, such as hydrocephalus, neoplastic conditions, either primary brain tumors or metastatic disease, infectious agents, inflammatory (non-infectious) disease such as granulomatous meningoencephalomyelitis, trauma, vascular disease, and primary or idiopathic epilepsy. Primary epilepsy is caused by a functional defect of the brain, and no structural abnormalities can be found in these dogs to account for the seizures. The disorder is heritable in several breeds of dogs and has a typical age of onset between 1 year and 5 years.
Historical information and examination findings are useful in directing the clinician to likely causes for the seizures. It is helpful to rank differential diagnoses based on the age of onset of seizures. Typically, extracranial causes are explored first, and if none are identified, then intracranial causes are pursued.