SYMPTOM
Seizures
Episodes of involuntary muscle activity, altered consciousness, or collapse lasting seconds to minutes.
Idiopathic Epilepsy
In many dogs and some cats, seizures occur without an identifiable structural or metabolic cause, a condition termed idiopathic epilepsy. This is thought to reflect an inherent predisposition to seizure activity within the brain's electrical circuitry, with certain breeds showing higher prevalence than others. Idiopathic epilepsy typically presents in younger to middle-aged animals and produces recurrent seizures that may follow recognisable patterns in terms of frequency, timing, and character. The diagnosis is generally reached by excluding other identifiable causes of seizure activity.
Structural Brain Disease
Conditions that physically affect brain tissue — including tumours, inflammatory diseases such as encephalitis, vascular events, congenital malformations, and traumatic injuries — can disrupt normal neuronal function and produce seizure activity. The location, size, and nature of the structural lesion influence the character of the seizures and any accompanying neurological signs. Animals with structural brain disease may show additional neurological abnormalities between seizures, such as changes in behaviour, vision deficits, circling, or head pressing, that reflect the effects of the lesion on surrounding brain tissue.
Metabolic and Systemic
The brain is exquisitely sensitive to changes in its chemical environment, and metabolic disturbances can lower the seizure threshold sufficiently to produce clinical seizure activity. Hypoglycaemia, hepatic encephalopathy from liver disease, severe electrolyte imbalances, uraemia from kidney failure, and certain endocrine disorders can all affect brain function to the point of triggering seizures. These metabolically driven seizures may occur in association with identifiable systemic illness and may resolve or recur in concert with fluctuations in the underlying metabolic parameter.
Toxic
Numerous substances can produce seizure activity through direct neurotoxic effects or by disrupting normal neurotransmitter function. Common toxins that may cause seizures include certain pesticides, rodenticides, plants, medications (both prescribed and accidental ingestions), and recreational drugs. Toxic seizures often have a relatively acute onset following exposure and may be accompanied by other toxicity signs that vary depending on the substance involved. The temporal relationship between potential exposure and seizure onset can be an important diagnostic clue.
Infectious
Infectious agents that reach the central nervous system — including viruses, bacteria, fungi, and protozoa — can produce inflammation within the brain (encephalitis) that may manifest as seizure activity. The specific infectious agents vary by geographic region and the animal's exposure history. Infectious causes of seizures may produce additional signs of systemic illness such as fever, lethargy, and appetite loss, alongside neurological signs, and the seizures may develop in the context of a broader illness rather than appearing in an otherwise healthy-appearing animal.
Reactive
Some seizures occur as a physiological response to a transient insult rather than reflecting chronic brain disease. These reactive seizures may be triggered by acute metabolic crises, fever, certain medications, or abrupt withdrawal from substances that affect the nervous system. They may occur as isolated events that do not recur once the triggering factor is resolved, or they may indicate a temporary lowering of the seizure threshold that returns to normal once the underlying cause is addressed.
Why timing matters
Early observation
A first seizure is a significant event that warrants careful documentation regardless of its duration or apparent severity. The animal's age at first seizure can provide useful context — onset between roughly one and five years of age in dogs may suggest idiopathic epilepsy, while onset in very young animals or in older animals may raise different considerations. The circumstances surrounding the first seizure, the animal's behaviour before and after, the duration and character of the event, and any potential exposure to toxins or recent illness all contribute valuable information. Some animals experience a single seizure that never recurs, while for others the first seizure marks the beginning of a recurring pattern.
Later presentation
As seizure activity recurs, the pattern of recurrence becomes an important part of the clinical picture. The frequency of episodes, whether they are increasing or stable, the consistency of seizure character, and the inter-ictal period (the time and behaviour between seizures) all provide information. Some animals develop a recognisable pattern — seizures at consistent intervals, clusters at predictable times, or events triggered by identifiable stimuli. Changes in seizure frequency, duration, or character over time may reflect progression of an underlying condition or may influence management decisions.
The long-term trajectory of seizure disorders varies considerably. Idiopathic epilepsy may remain relatively stable or may show a gradually increasing frequency over years. Structural brain diseases may produce a more consistently progressive course with changing seizure patterns. Metabolic causes may produce seizures that fluctuate with the underlying condition. Maintaining a detailed seizure diary — recording dates, times, durations, pre-seizure behaviour, post-seizure recovery, and any potential triggers — creates an invaluable longitudinal record that can reveal patterns and track the condition's trajectory over months and years.
Conditions commonly associated
Epilepsy in Dogs
Feline Infectious Peritonitis (FIP)
Seizures may occur in the non-effusive (dry) form of FIP when granulomatous inflammation involves the brain, reflecting immune-mediated vasculitis and inflammatory lesion formation within the central nervous system.
Systemic Hypertension in Cats
Severe hypertension can cause neurological complications including seizures when blood pressure damages brain tissue.
Epilepsy in Cats
Epilepsy in cats can cause seizures ranging from subtle facial twitching to full tonic-clonic convulsions. Feline seizures often appear differently than in dogs and may include unusual behavioural changes.
Portosystemic Shunt
Severe accumulation of toxins, particularly ammonia, in portosystemic shunt cases can trigger seizure activity.
When to explore further
Any first-time seizure warrants documentation and consideration, as the initial event establishes a baseline and the circumstances surrounding it may provide important diagnostic information. The animal's age, breed, health history, and the specific character of the seizure all contribute to understanding what the event may represent.
Seizures that increase in frequency, duration, or intensity over time may suggest a progressive underlying process. A change in an established seizure pattern — such as more frequent episodes, longer recovery periods, or the development of new seizure types — can be particularly significant and warrants updated assessment.
Cluster seizures, where multiple seizure events occur within a 24-hour period, represent a different clinical situation from isolated events separated by weeks or months. The clustering pattern may influence management approaches and the urgency with which the situation is assessed.
Seizures that are accompanied by neurological abnormalities between episodes — such as behaviour changes, vision deficits, circling, head tilting, or altered consciousness — may suggest structural brain disease rather than idiopathic epilepsy. The presence of inter-ictal neurological signs can be an important distinguishing factor.
A seizure occurring in an older animal that has not previously had seizure activity may carry different implications compared with new-onset seizures in a young adult. The age of onset influences the range of likely underlying causes and may guide the investigative approach.
Creating a detailed seizure diary is one of the most valuable actions an owner can take. Recording the date, time, duration of each event, the animal's behaviour before and after, and any potential triggers builds a dataset that becomes increasingly informative over time. Video recording of seizure events is exceptionally useful, as it captures details about the character of the seizure — which limbs are involved, whether consciousness appears preserved, the specific movements observed — that can be difficult to describe accurately from memory, particularly given the emotional distress of witnessing a seizure. Ensuring the animal's environment is safe during and after seizures, by moving sharp objects and preventing falls from heights, helps reduce the risk of injury during events.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS