Few clinical presentations create as much diagnostic confusion in practice as a collapsing patient. Was it a seizure? Was it syncope? Or was it something else entirely?
Misclassification matters. Treating syncope as epilepsy or ignoring status epilepticus as a “fainting episode” can delay life-saving intervention. This article breaks down the key differences, diagnostic approach, and treatment principles every veterinarian must master.
Syncope or Seizure: Why the Distinction Is Difficult
At first glance, syncope and seizures may look identical to owners:
- Sudden collapse
- Loss of consciousness
- Possible paddling or rigidity
- Rapid recovery
But despite similar appearances, their pathophysiology, causes, and treatments are fundamentally different.
A systematic approach is essential.
What Is Syncope?
Syncope is a transient loss of consciousness caused by inadequate delivery of oxygen or glucose to the brain.
Most cases are:
- Cardiovascular in origin
- Neurogenic or metabolic less commonly
The key feature of syncope is global cerebral hypoperfusion, not abnormal electrical activity.
Common Causes of Syncope
Cardiovascular Causes
- Arrhythmias
- Congenital or acquired heart disease
- Thromboembolic disease
- Acute blood loss
- Severe hypotension
Neurologic Causes
- Brain neoplasia
- Thromboembolic disease
- Trauma
Metabolic Causes
- Hypoglycemia
- Insulin-secreting tumors
- Insulin overdose
- Glycogen storage diseases
- Starvation (especially toy breeds)
- Digitalis intoxication
- Iatrogenic drug effects
What Is a Seizure?
A seizure is a clinical manifestation of abnormal, excessive neuronal excitation in the brain.
Unlike syncope, seizures are caused by electrical dysfunction, not perfusion failure.
Seizures may be:
- Idiopathic (epilepsy)
- Structural (tumors, inflammation, trauma)
- Metabolic or toxic
Initial Clinical Approach: Syncope or Seizure?
The first rule is this:
Treat what kills first.
Regardless of cause, immediately assess and stabilize:
- Airway
- Breathing
- Circulation
- Temperature
Life-threatening problems such as severe hemorrhage, hypoglycemia, hypotension, or hyperthermia must be addressed before chasing a definitive diagnosis.
Once stabilized, you can begin sorting out the cause.
Diagnostic Work-Up: Start Simple
Always begin with a minimum database:
- CBC
- Serum biochemistry
- Blood glucose
- Urinalysis
These tests alone can identify many causes of both syncope and seizures.
Additional diagnostics may include:
- Electrocardiogram (ECG)
- Thoracic radiographs
- Advanced imaging (CT/MRI)
- Cerebrospinal fluid analysis
Diagnostics should be guided by clinical suspicion, not habit.
When the Client Cannot Afford a Full Work-Up
This is real life.
When finances are limited:
- Prioritize treatable and immediately life-threatening conditions
- Avoid expensive diagnostics that do not change short-term management
- Do not default to MRI if follow-up treatment is not feasible
Good medicine is not about ordering everything. It is about ordering wisely.
How Do You Treat Syncope?
There is no single drug for syncope.
Treatment focuses on:
- Identifying and correcting the underlying cause
- Supporting cardiovascular stability
- Managing metabolic derangements
Many animals will not experience another episode once the trigger is removed.
How Is a Seizing Patient Treated?
A patient in status epilepticus is a medical emergency.
First-Line Emergency Therapy
Diazepam:
0.5–1 mg/kg IV
May be repeated up to 3 doses
If diazepam fails:
Second-Line Therapy
Phenobarbital:
2–4 mg/kg IM or IV
OR constant-rate infusion at 3–16 mg/hour
Refractory Seizures
Pentobarbital:
3–15 mg/kg IV to effect
What Else Must You Monitor in Seizing Patients?
Seizures are not just neurologic events. They are systemic emergencies.
Monitor and manage:
- Hyperthermia (active cooling may be required)
- Cerebral edema after prolonged seizures
Treatment may include:
- Mannitol
- Anti-inflammatory therapy (e.g., corticosteroids)
Long-Term Seizure Control
First-Line Maintenance Drug
Phenobarbital
Starting dose: 2 mg/kg twice daily
Loading dose: 6–10 mg/kg if rapid control is needed
If higher doses are required:
Add potassium bromide at 30 mg/kg/day
Reduce phenobarbital dose if possible
Other drugs such as primidone or phenytoin are not recommended in small animals except as a last resort.
Side Effects You Must Explain to Clients
Phenobarbital
Sedation
Polyphagia
Transient effects usually resolve in 5–7 days
Long-term risk: hepatic toxicity
Potassium Bromide
Gastrointestinal upset
CNS depression at high doses
Advantage: eliminated by kidneys, useful in liver disease patients
Final Thoughts
Syncope and seizures may look the same, but they are not the same disease.
One is a perfusion problem.
The other is an electrical problem.
Confusing the two leads to wrong treatment, delayed care, and avoidable deaths.
The best clinicians do not guess.
They stabilize first, think clearly, and act decisively.
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