Neurology · Seizure Disorders
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Seizures typically occur when serum Na⁺ < 120 mEq/L or with a rapid drop in sodium, classically from SIADH, psychogenic polydipsia, or MDMA use.
Hypertonic (3%) saline as a 100-150 mL IV bolus over 10 minutes is the absolute first-line therapy and can be repeated until seizures stop.
A stat serum sodium is the definitive test; a point-of-care VBG/ABG with electrolytes gives the fastest result.
Standard antiepileptics (benzodiazepines) are often ineffective without correcting the sodium.
The acute goal is to raise serum sodium by 4-6 mEq/L to reverse cerebral edema.
Do not exceed an 8 mEq/L rise in 24 hours once symptoms resolve, to prevent osmotic demyelination syndrome.
Pathophysiology is free water shifting intracellularly causing astrocyte swelling and cerebral edema, which untreated progresses to brainstem herniation.
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A 22-year-old woman is brought to the emergency department after a generalized tonic-clonic seizure at a music festival. Friends report she drank large amounts of water and took ecstasy. She is now obtunded with another seizure in progress. A stat basic metabolic panel returns a serum sodium of 116 mEq/L. Two doses of IV lorazepam have failed to stop the seizure activity.
Which of the following is the most appropriate next step in management?
Administer a 100-150 mL IV bolus of 3% hypertonic saline.
Severe hyponatremic seizures are refractory to benzodiazepines until sodium is corrected. A bolus of 3% hypertonic saline rapidly raises serum sodium by 4-6 mEq/L to reverse cerebral edema, while keeping the total 24-hour rise under 8 mEq/L to avoid osmotic demyelination.
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Etiology / Epidemiology
Typically occurs when serum Na⁺ < 120 mEq/L or with a rapid drop in sodium levels, classically triggered by SIADH, psychogenic polydipsia, or MDMA use.
Clinical Manifestations
Presents as altered mental status rapidly progressing to generalized tonic-clonic activity and status epilepticus, indicating impending brain herniation.
Diagnosis
Diagnosed via stat basic metabolic panel (BMP) or point-of-care blood gas showing severe hyponatremia.
Treatment
Hypertonic (3%) saline is the absolute first-line therapy, administered as a 100-150 mL IV bolus.
Prognosis
Untreated episodes lead to fatal cerebral edema, while overcorrection risks osmotic demyelination syndrome.
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Epidemiology & Etiology
Most common in patients with acute hyponatremia developing in < 48 hours. Classic board triggers include acute water intoxication (psychogenic polydipsia, marathon runners), MDMA (ecstasy) intoxication, and severe SIADH (e.g., small cell lung cancer). Postoperative patients receiving hypotonic fluids are also at high risk for this neurologic emergency.
Pertinent Anatomy
The rigid cranial vault cannot accommodate significant brain tissue expansion. The primary structures affected are the cerebral hemispheres, leading to generalized seizures, and the brainstem, which is vulnerable to uncal herniation.
Pathophysiology
A sudden drop in extracellular osmolality creates an osmotic gradient that drives free water into the intracellular space. This leads to astrocyte swelling and acute cerebral edema. The resulting increased intracranial pressure (ICP) decreases cerebral perfusion and triggers neuronal hyperexcitability, culminating in seizure activity. If uncorrected, this progresses to brainstem herniation and respiratory arrest.
Clinical Manifestations
Early signs include headache, nausea, and delirium. As Na⁺ falls < 120 mEq/L, patients develop generalized tonic-clonic seizures. This is a life-threatening emergency that may rapidly progress to coma, decerebrate posturing, and respiratory failure.
Diagnosis
A stat serum sodium level is the definitive diagnostic test, typically revealing Na⁺ < 120 mEq/L. Point-of-care venous blood gas (VBG) or arterial blood gas (ABG) with electrolytes provides the fastest result. While a head CT is often performed to rule out intracranial hemorrhage, it should never delay hypertonic saline administration if severe hyponatremia is known.
Treatment
The immediate intervention is a 100-150 mL IV bolus of 3% hypertonic saline over 10 minutes, which can be repeated until seizures stop. Standard antiepileptic drugs (e.g., benzodiazepines) are often ineffective without sodium correction. The goal is an acute rise in serum sodium by 4-6 mEq/L to reverse cerebral edema. Do not exceed an increase of 8 mEq/L in 24 hours once symptoms resolve to prevent severe neurologic complications.
Prognosis
Rapid resolution of seizures occurs with appropriate hypertonic saline administration. However, overzealous correction of chronic hyponatremia causes osmotic demyelination syndrome (central pontine myelinolysis), presenting days later as locked-in syndrome. Untreated acute hyponatremic seizures carry a high mortality rate due to cerebral herniation.
Differential Diagnosis
1. Hypoglycemic seizure: Diagnosed with a stat point-of-care glucose showing < 50 mg/dL.
2. Status epilepticus (primary): Typically responds to first-line IV lorazepam and lacks severe electrolyte derangements.
3. Eclampsia: Occurs in pregnant or postpartum women and requires IV magnesium sulfate.
4. Intracranial hemorrhage: Presents with sudden-onset focal neurologic deficits or thunderclap headache and is confirmed via non-contrast head CT.