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| THe CanIne SeIzuRe PaTIenT: FouR IMPoRTanT QueSTIonS Today's Veterinary Practice May/June 2014 32 tvpjournal.com events (Figures 1–3). However, EEG is not a readily avail- able clinical tool in veterinary medicine, and a first-time EEG recorded between seizures in an epileptic human or dog has about a 25% chance of identifying the event as a seizure. 7 Observation Identification of a seizure is most often achieved by compar- ing the observed event to what is considered a typical seizure. • Generalized tonic clonic seizures typically last 1 to 2 minutes, and characteristically feature loss of conscious- ness, muscle tone and movement (tonic/clonic), jaw chomping, and profuse salivation, followed by gradual return to consciousness and normal ambulation. • Partial or nonconvulsive seizures are more difficult to recognize, with the latter requiring an EEG recording during the event. 8 In human medicine, classifying events by description alone (without EEG) is accurate, but also allows overdiag- nosis of nonepileptic events as seizures. Therefore, obser- vation has high sensitivity, low specificity, and low positive predictive value. 9 Accordingly, clinicians should be aware that they may be treating nonepileptic events with an AED. 10 2 DOES THE SEIZURE HAVE AN UNDERLYING CAUSE? Identifying an underlying cause for the seizure yields better seizure control, quality of life, and accurate prognosis. The most recent seizure classification system— by cause—groups seizures into 3 causes: genetic, structural/ metabolic, and unknown. Genetic & Unknown Causes Diagnosis of idiopathic epilepsy (IE) is made when: • Genetic basis is suspected • Testing has failed to reveal a cause for the seizure. Structural/Metabolic Causes • Diagnosis of structural epilepsy is often made by mag- netic resonance imaging (MRI) and cerebrospinal fluid (CSF) analysis, with common causes, including brain tumor, infarct or hemorrhage, or encephalitis. • Technically, most metabolic causes of seizure are not a form of epilepsy because the brain itself is normal and reacting to an extracranial insult, which once eliminated, results in cessation of seizure. Because MRI and CSF analysis are expensive and not readily available, the primary care clinician is often faced with making a difficult decision about whether to refer a patient or simply prescribe an AED. Key factors in assessing a seizure patient include: Age As a guideline, dogs with IE typically have their first seizure between 6 months and 6 years of age. However, at seizure onset, about 20% of dogs older than 6 years, and 2% of dogs younger than 6 months, do not have an identifiable cause for seizure. 11 Breed There are, however, some exceptions to the age rule noted above. Seizure is a very common presenting complaint in Figure 1. A 3-year-old collie mix was presented for cluster seizure; this image shows the patient during a generalized tonic clonic seizure. Another seizure was recorded by EEG and on video (see page 35). Figure 2. EEG recorded under dexmedetomidine seda- tion in a double banana montage with electrocardiog- raphy; the patient was not demonstrating a clinical sei- zure at this point in the EEG. The red arrow indicates first appearance of generalized sharp waves most promi- nent in the frontal parietal area, which indicates the pres- ence of electrical activity consistent with a seizure, even though the patient was not actively seizuring at the time. Figure 3. EEG recorded while the patient is experi- encing an electrical and clinical generalized tonic clon- ic seizure, demonstrating more frequent and higher amplitude generalized sharp waves. TVP_2014-0506_Seizure Patient.indd 32 5/24/2014 10:44:52 AM