Reactive Seizures in Cats: Recognising Metabolic, Toxic and Systemic Causes

A cat can have a seizure even when the primary problem lies outside the brain. Hypoglycaemia, electrolyte disturbances, hepatic dysfunction, intoxication and other systemic abnormalities can produce reactive seizures, making the initial laboratory assessment an important part of seizure investigation. 

Reactive seizures are caused by extracranial factors, such as toxin exposure or metabolic disease^[1]. Unlike structural epilepsy, the seizure itself is not caused by an intracranial lesion. 

Start with Metabolic Screening 

Haematology and serum biochemistry should be performed to investigate possible metabolic causes. These tests can help identify hepatic or renal encephalopathy, hypertriglyceridemia, polycythaemia vera and severe anaemia^[2]. 

Glucose and electrolyte assessment is particularly important because several abnormalities can be associated with seizures, including: 

• Hypoglycaemia or hyperglycaemia 
• Hypocalcaemia or hypomagnesaemia 
• Hyponatraemia or hypernatraemia 
• Hypokalaemia 

Laboratory abnormalities should be interpreted alongside the cat's clinical findings rather than treated as isolated explanations for the seizure. 

Investigate Possible Hepatic Encephalopathy 

When hepatic disease is suspected, pre- and postprandial serum bile acid testing can support investigation for a portosystemic shunt or other forms of hepatic impairment. 

Ammonia testing is also recommended when hepatic disease is a concern. However, interpretation requires caution because transient postictal increases in ammonia concentrations have been reported in epileptic cats without liver disease. In such cases, repeating the measurement 3 days after the seizure may provide more useful information^[3]. 

This distinction is clinically important when an increased ammonia concentration could otherwise be interpreted as evidence of primary hepatic disease. 

Consider Endocrine and Nutritional Causes^[2] 

Thyroid hormone testing should be performed to rule out hyperthyroidism. 

Thiamine deficiency is another recognised cause of seizures in cats. The dietary history can therefore provide an important diagnostic clue. Thiamine deficiency may be associated with poorly processed or heat-treated diets, sulphite-preserved foods such as certain pet meats, or diets containing thiaminase, including raw fish. These factors can interfere with thiamine availability or absorption. 

Serum vitamin B12 testing may also be appropriate in selected cases when hypocobalaminaemia needs to be investigated. 

Urine metabolic screening has a more specific role. It may help identify some lysosomal diseases or inborn errors of metabolism, including methylmalonic aciduria, but should generally be reserved for cases in which there is a high index of suspicion. 

Keep Toxins High on the List^[2] 

Intoxication is the most common cause of reactive seizures in cats, and exposure may be presumed or confirmed. Importantly, routine blood testing may remain unremarkable despite toxic exposure. 

This means a normal laboratory profile does not necessarily exclude a reactive seizure caused by intoxication. A detailed history should therefore accompany laboratory investigation, particularly when there is any possibility of toxin exposure. 

The differential list provided for feline seizures includes ethylene glycol, lead, organophosphates and pyrethroids among toxic causes. 

When Should the Investigation Move Beyond Metabolic Causes? 

The purpose of metabolic screening is not simply to collect laboratory values. It helps determine whether an extracranial explanation can account for the seizure. 

If an appropriate evaluation identifies a systemic, metabolic or toxic cause, investigation can be directed accordingly. Conversely, when reactive causes have been ruled out, the diagnostic pathway should move towards investigating possible intracranial disease with advanced imaging. 

Clinical Bottom Line 

Reactive seizures require a systematic search for extracranial triggers. Metabolic screening, targeted hepatic and endocrine testing, dietary assessment, and careful consideration of intoxication should form the initial diagnostic approach. A normal blood profile does not exclude intoxication, while abnormalities such as increased ammonia require appropriate clinical interpretation. Once reactive causes have been adequately considered or excluded, investigation can proceed towards possible intracranial disease.

References:

1. Hazenfratz M, Taylor SM. Recurrent seizures in cats: Diagnostic approach–when is it idiopathic epilepsy?. Journal of feline medicine and surgery. 2018 Sep;20(9):811-23. https://journals.sagepub.com/doi/pdf/10.1177/1098612X18791873
2. Sivolapenko D, Lowrie M. Epileptic seizures in cats: practical approaches to diagnosis. Journal of Feline Medicine and Surgery. 2026 Feb;28(2):1098612X251407905. https://journals.sagepub.com/doi/pdf/10.1177/1098612X251407905
3. Nilsson CH, Svensson MB, Säve SJ, Van Meervenne SA. Transient hyperammonaemia following epileptic seizures in cats. Journal of feline medicine and surgery. 2021 Jun;23(6):534-9. https://journals.sagepub.com/doi/pdf/10.1177/1098612X20962747