Cognitive dysfunction in naturally occurring canine idiopathic epilepsy

Abstract

Globally, epilepsy is a common serious brain disorder. In addition to seizure activity, epilepsy is associated with cognitive impairments including static cognitive impairments present at onset, progressive seizure-induced impairments and co-morbid dementia. Epilepsy occurs naturally in domestic dogs but its impact on canine cognition has yet to be studied, despite canine cognitive dysfunction (CCD) recognised as a spontaneous model of dementia. Here we use data from a psychometrically validated tool, the canine cognitive dysfunction rating (CCDR) scale, to compare cognitive dysfunction in dogs diagnosed with idiopathic epilepsy (IE) with controls while accounting for age. An online cross-sectional study resulted in a sample of 4051 dogs, of which n = 286 had been diagnosed with IE. Four factors were significantly associated with a diagnosis of CCD (above the diagnostic cut-off of CCDR ≥50): (i) epilepsy diagnosis: dogs with epilepsy were at higher risk; (ii) age: older dogs were at higher risk; (iii) weight: lighter dogs (kg) were at higher risk; (iv) training history: dogs with more exposure to training activities were at lower risk. Impairments in memory were most common in dogs with IE, but progression of impairments was not observed compared to controls. A significant interaction between epilepsy and age was identified, with IE dogs exhibiting a higher risk of CCD at a young age, while control dogs followed the expected pattern of low-risk throughout middle age, with risk increasing exponentially in geriatric years. Within the IE sub-population, dogs with a history of cluster seizures and high seizure frequency had higher CCDR scores. The age of onset, nature and progression of cognitive impairment in the current IE dogs appear divergent from those classically seen in CCD. Longitudinal monitoring of cognitive function from seizure onset is required to further characterise these impairments.

Fig 1. Probability of being affected by canine cognitive dysfunction (CCD) by age in dogs with epilepsy (n = 286) and controls (n = 3765).

Results based on a generalised linear model with CCD as the binary outcome variable.

Fig 2. Probability of being affected by canine cognitive dysfunction (CCD) across weight (kg) in the control population.

N.B. Age is kept constant (8 years old) to examine the effect of weight in isolation.

Fig 3. Probability of being affected by canine cognitive dysfunction (CCD) by age in dogs with epilepsy (n = 286) and controls (n = 3765).

Data are based on a generalised linear model with CCD as the binary outcome variable.

Fig 4. Effect of idiopathic epilepsy on CCDR score across age (years) in dogs with idiopathic epilepsy (n = 286) and controls (n = 3765).