Clinical and Electroencephalographic Findings of Inflammatory and Infectious Diseases of the Central Nervous System in Dogs: a Retrospective Study

In the present study medical records of 97 dogs with inflammatory/infectious diseases of the central nervous system (CNS), including 26 dogs with a history of seizures, were retrospectively examined. The aims of the study were to analyse the incidence rate of seizures, to search for criteria to recognize specific inflammatory diseases and to determine how far electroencephalography may be useful in the early confirmation of encephalitis and encephalitis-associated seizures. The incidence rate of seizures in this dog population was 26.8%, and dogs with protozoal encephalitis had the highest rate. Signalment, history, extraneural and neurological signs including localization contributed only a little to a specific diagnosis. Surprisingly focal clinical signs were observed in two-thirds of the dogs. Either focal or multifocal clinical signs were related mainly to the forebrain in dogs with a history of seizures and to the brainstem in dogs without seizures. Cerebrospinal fluid (CSF) analyses were useful to separate encephalitis from other CNS diseases and to distinguish certain conditions from others in approximately half the cases. Electroencephalography (EEG) revealed two distinct patterns in 25 examined dogs with histopathologically confirmed disease entities, which were characterized by high voltage, slow activity (HVSA) with superimposed low voltage, fast activity (LVFA). These changes were consistent and no significant differences (P > 0.05) between dogs with and without seizures, nor between different disease entities, were noted. However, all the dogs with seizures had in addition a uniform paroxysmal EEG activity with a high voltage (mean = 106.3 microV), fast activity (mean = 8.5 Hz) pattern. Moreover in several dogs from the present study this pattern had a focal distribution despite the fact that clinically seizures appear generalized. Therefore it was concluded that EEG may be a very helpful diagnostic tool to confirm an early diagnosis of encephalitis and to separate potential seizure cases from those without seizures.