High-Field MRI Unveils Hidden Causes of Epilepsy in Dogs with Normal Neurological Examinations

Epilepsy is a common neurological condition in dogs, characterized by recurrent seizures that can disrupt both the affected animal’s quality of life and its owners' sense of security. Despite being a frequent diagnosis, the underlying causes of epilepsy often remain elusive, especially when dogs present with normal neurological examinations between seizure episodes. A new study led by Stephanie Phillipps and Rita Goncalves sheds light on the use of high-field MRI to explore potential structural causes of epilepsy in these dogs. This research adds valuable insights into the diagnostic challenges faced by veterinarians and underscores the importance of advanced imaging techniques.

Study Design and Methodology

The study, which analyzed the medical records of 412 dogs, aimed to investigate high-field MRI findings in dogs with epilepsy, specifically those who had a normal inter-ictal neurological examination—meaning their neurological health appeared typical between seizures. These dogs had undergone high-field MRI scans at either 1.0T or 1.5T strength, while also having metabolic and toxic causes of epilepsy ruled out.

Inclusion in the study required at least two epileptic seizures that were spaced more than 24 hours apart, along with a normal neurological exam during the inter-ictal period. By excluding dogs with other potential causes of seizures, the study focused on identifying structural abnormalities that might contribute to epilepsy.

Key Findings: A Rare Structural Cause

The results revealed that structural abnormalities were relatively rare among the 412 dogs included in the study. Overall, 76 dogs (18.5%) showed some form of abnormality on MRI scans. However, most of these findings (78.9%) were deemed incidental and not likely related to the seizures. Only 16 dogs (3.9%) were diagnosed with a structural cause of their epilepsy. The most common cause identified was neoplasia (tumors), which was found in 13 dogs (81.3%). Other structural causes included anomalous brain structure in two dogs (12.5%) and meningoencephalitis of unknown origin (MUO) in one dog (6.3%).

Age and Status Epilepticus: Predictors of Structural Disease

The study also explored the relationship between the age of onset for the first epileptic seizure and the likelihood of structural lesions. Notably, the occurrence of structural causes increased with age. Among dogs younger than one year, no structural causes were found. However, as the dogs aged, the likelihood of a structural cause rose. For example, among dogs aged 1 to 6 years, 1.6% had a structural cause; this increased to 23.1% in dogs older than eight years.

Additionally, the study identified two significant risk factors for structural disease. The first was an older age at the time of the first epileptic seizure (with dogs diagnosed later in life more likely to have a structural cause). The second was a history of status epilepticus (a prolonged seizure episode), which increased the likelihood of finding a structural lesion.

Implications for Veterinary Practice

The findings from this study are significant for veterinary practitioners who treat epileptic dogs, especially those whose neurological exams appear normal between seizures. While structural causes of epilepsy are relatively rare in these cases, they are more likely to be found in older dogs or those with a history of status epilepticus. High-field MRI emerges as an important tool in diagnosing these rare but impactful conditions.

This research challenges the assumption that a normal neurological exam between seizures always rules out structural causes of epilepsy. It highlights the importance of considering advanced imaging when dealing with cases of epilepsy that do not respond to typical treatment or when other causes remain unexplained. As the study demonstrates, structural abnormalities, though uncommon, can have significant consequences for diagnosis and treatment planning.

In conclusion, while structural lesions are an uncommon cause of epilepsy in dogs with normal inter-ictal neurological exams, advanced imaging techniques such as high-field MRI can help uncover hidden issues. This study provides valuable information for veterinarians seeking to understand the full range of potential causes of seizures in dogs and emphasizes the need for careful diagnostic workups in cases of unexplained epilepsy. With further research, we may gain a deeper understanding of how to best address these challenging cases and improve outcomes for epileptic dogs.

Read full article here: https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1507861/full