Two conditions, both starting with »s«. But that is not their only similarity. Although their causes are different, they can look very similar and therefore can be confused. To differentiate between them is important for diagnosis and treatment, and a careful description of animal’s behaviour before, during and following the collapse can be very helpful.
Syncope or fainting is transient loss of consciousness, associated with loss of postural tone, caused by reduced cerebral blood flow and insufficient oxygen or glucose delivery to the brain. It usually has fast onset, short duration and spontaneous recovery and can follow effort or excitement. It can be caused by number of cardiac (arrhythmias, ventricular outflow obstruction, impaired cardiac output or filling …) and noncardiac (pulmonary hypertension or thromboembolism, hypoglycaemia, anaemia, sudden haemorrhage, electrolyte imbalance, narcolepsy …) abnormalities.
In patient we can see rear limb weakness or sudden collapse, lateral recumbency, stiffening of the forelimbs, opisthotonos, micturition and vocalization. What we usually don’t see with a syncope is tonic-clonic motion, facial fits, defecation, aura, postictal dementia and neurologic deficit. Animal returns to completely normal state after the collapse.
A seizure is a period of symptoms due to abnormal electrical activity in the brain. Abnormalities causing it can originate intracranially (congenital anomalies, neoplasia, inflammation, trauma …) or extracranially (toxic, metabolic, endocrine disorders, liver disease …), or the seizure can be idiopathic. Clinical signs of seizures can be separated into four parts: the prodrome, aura, ictal period and postictal period.
The prodrome is the time before seizure, when the owners may observe unusual behaviour (hiding, whining, attention seeking …). It can be barely recognizable or very obvious. The aura are symptoms, just moments before the seizure onset. Animal can be showing stereotypical activity (pacing, licking), autonomic patterns (salivation, vomiting, urination) or abnormal behaviour (barking, attention seeking). The ictal period is the time of actual seizure which usually lasts seconds to minutes. Seizures are mostly generalized tonic-clonic; the animal falls into lateral recumbency, exhibits rhythmic contractions and relaxation of muscles, which is seen as paddling of the limbs, jerking movements and jaw chomping. Salivation, involuntary urination and defecation can be seen, and the animal is usually unconscious. Less commonly we can see focal partial motor seizures (focal twitching, local tonic-clonic contraction of the facial or limb muscles). The postictal period follows seizure and can last up to several hours – animals may behave abnormally, be disoriented, somnolent, showing altered thirst or appetite and have neurological deficits. Seizures are the only condition that should have an associated postictal period.
Nelson R. W., Couto C. G.: Small Animal Internal Medicine, 4th Ed