Idiopathic epilepsy

21 Idiopathic epilepsy




INITIAL PRESENTATION


Seizures.



INTRODUCTION


The definition of idiopathic epilepsy is the ocurrence of seizures for which an underlying cause has not been found. It is a diagnosis made by exclusion of other aetiologies.


A presumptive diagnosis is made after:


• at least two seizures have been observed

• the physical and neurological examinations are normal during the inter-ictal period

• no behavioural abnormalities are observed while the animal is at home

• normal lab tests (haematology, biochemistry, urine) and diagnostic imaging (CT, MRI) .


SIGNALMENT


A 4-year, 10-month-old male golden retriever.



CASE HISTORY


A generalized tonic-clonic seizure occurred while the dog was walking on the beach. This was followed by a normal inter-ictal period and then another seizure, similar in nature, 2 weeks later. Phenobarbitone had been commenced. No exercise intolerance was reported. The dog was described as being otherwise normal.



CLINICAL EXAMINATION


The dog was alert ambulatory, with a normal gait, postural reactions and proprioception. The right menace response was absent but facial muscle function was normal.


The right pupil was slightly larger than the left. When light was shone into the right eye, neither pupil constricted. When light was shone in the left eye the right and left pupils constricted. The right optic disc was darker than the left suggesting a lack of myelin. The other CNN were normal as were the spinal reflexes.



NEUROANATOMICAL LOCALIZATION


The absent menace response and PLR in the right eye indicated a CN II lesion. Seizures are a sign of cerebral disease. The dark optic disc suggesting demyelination of the optic disc suggested a long-term lesion, and so the two lesions may have been unrelated.



DIFFERENTIAL DIAGNOSIS



• Optic nerve atrophy

• Idiopathic epilepsy

• Lesion of the optic chiasm compressing the thalamus would be expected to alter mentation and vision.


CASE WORK-UP



• MRI of the head was normal

• CSF was normal

• Ophthalmology consultation diagnosed right optic nerve atrophy.


DIAGNOSIS


Two separate lesions. The cause of the seizures was not found. Idiopathic epilepsy.


Seizures occur in 1–3% of dogs, with idiopathic epilepsy accounting for about 20–80% of those seizures, depending on the reference. It has a proven inheritance in a number of canine breeds but can also affect crossbreds. Do not breed from affected animals. Idiopathic epilepsy also occurs in cats. The incidence of idiopathic epilepsy in cats varies greatly. One source states that 60% of seizuring cats had idiopathic epilepsy.


There is no established range for the age of onset of idiopathic epilepsy in cats; it may be from 3 months to 16 years. In a study of 12 cats, the age range at onset of seizures was 0.25–12 years with a median age of 2 years. The age of onset in dogs is between 1 and 5 years of age.



PROGNOSIS


A total of 15% of affected dogs show a spontaneous remission (freedom from seizures for more than 3 years without anticonvulsants) or remission with treatment (seizure free for more than 3 years while on anticonvulsants).


Approximately 25% of idiopathic epileptic dogs are refractory to treatment. Examine all aspects of the case for errors (incorrect diagnosis, or inadequate use of drugs); 20–40% are refractory to initial monotherapy with anticonvulsants.


Idiopathic epilepsy is not thought to shorten the lifespan of affected dogs; however another source states that 19% of dogs die of causes directly related to their seizure disorder.





Seizure pattern



• The type, number and frequency of occurrence varies from animal to animal regardless of the aetiology.

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Idiopathic epilepsy

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