Overview
Definition:
Hyponatremic seizures are defined as epileptic seizures occurring in the setting of serum sodium levels below the normal range (typically < 135 mEq/L)
They are a critical manifestation of severe symptomatic hyponatremia, particularly in infants and children, and represent a neurological emergency requiring prompt and careful management to prevent permanent brain damage or death.
Epidemiology:
Hyponatremia is the most common electrolyte disorder encountered in pediatric hospital admissions, with seizures occurring in approximately 5-10% of symptomatic hyponatremic patients
Infants and young children are at higher risk due to their immature renal function, higher water turnover, and increased susceptibility to cerebral edema from rapid osmotic shifts.
Clinical Significance:
Hyponatremic seizures are a medical emergency due to the risk of severe neurological injury, including cerebral edema, herniation, and permanent cognitive deficits
Accurate and timely diagnosis is crucial, as misdiagnosis can lead to inappropriate treatments that worsen the condition
Understanding the pathophysiology and appropriate management, especially the nuances of hypertonic saline administration, is vital for all pediatric residents preparing for DNB and NEET SS exams.
Clinical Presentation
Symptoms:
Seizure activity, which may be generalized tonic-clonic, focal, or subtle
Lethargy and decreased level of consciousness
Vomiting, sometimes projectile
Irritability and poor feeding in infants
Headache and confusion in older children
Symptoms of underlying cause of hyponatremia, such as dehydration, polydipsia, or endocrine disorders.
Signs:
Neurological examination may reveal altered mental status, focal neurological deficits, or signs of increased intracranial pressure like papilledema
Signs of dehydration if that is the cause
In some cases, children may appear relatively well despite severe hyponatremia.
Diagnostic Criteria:
Diagnosis is confirmed by the presence of a seizure in a patient with documented hyponatremia (serum sodium < 135 mEq/L)
The severity of hyponatremia and the rapidity of its onset are key factors in determining the risk and severity of neurological manifestations
Serial monitoring of serum sodium levels is essential.
Diagnostic Approach
History Taking:
Detailed history of fluid intake and output
Recent illnesses (vomiting, diarrhea, fever)
Medications, especially diuretics or antipsychotics
History of polydipsia or polyuria
Family history of hyponatremia or seizures
Onset and character of seizure activity
Any associated symptoms like nausea, headache, or abdominal pain.
Physical Examination:
Complete neurological examination to assess level of consciousness, focal deficits, and signs of increased intracranial pressure
Assess hydration status (skin turgor, mucous membranes, capillary refill)
Evaluate for any underlying causes such as endocrine abnormalities or central nervous system pathology.
Investigations:
Essential: Serum electrolytes (sodium, potassium, chloride, bicarbonate), blood urea nitrogen (BUN), creatinine, serum osmolality
Urine electrolytes and osmolality to assess renal concentrating ability and distinguish between SIADH, diuretic-induced hyponatremia, or other causes
Glucose and calcium levels
Liver function tests
Thyroid function tests
Consider cortisol levels if adrenal insufficiency is suspected
Brain imaging (CT or MRI) may be indicated to rule out structural lesions or assess for cerebral edema, especially if the diagnosis is uncertain or there are focal neurological findings
Electroencephalogram (EEG) to characterize seizure activity.
Differential Diagnosis:
Other causes of seizures: metabolic derangements (hypoglycemia, hypocalcemia, hypomagnesemia), febrile seizures, epilepsy, infections (meningitis, encephalitis), intracranial hemorrhage, structural brain lesions, intoxication
Pseudohyponatremia (due to hypertriglyceridemia or hyperproteinemia).
Management
Initial Management:
Immediate management focuses on seizure control and gradual correction of severe hyponatremia to prevent osmotic demyelination syndrome (ODS)
If seizures are active, administer benzodiazepines (e.g., lorazepam 0.1 mg/kg IV)
If the hyponatremia is severe (serum sodium < 120 mEq/L) and causing seizures, cautious initial administration of 3% hypertonic saline is indicated
The goal is to raise serum sodium by 4-6 mEq/L in the first few hours to stop seizure activity.
Medical Management:
For hyponatremic seizures, the mainstay is the cautious intravenous administration of 3% hypertonic saline
The initial dose and rate of correction are critical and depend on the severity and chronicity of hyponatremia
**Dosing for Hyponatremic Seizures with 3% Saline:**
* **Initial Bolus:** For acute, symptomatic hyponatremia with seizures, administer 3% saline at 5-10 mL/kg over 10-20 minutes
This can be repeated once or twice if seizures persist, aiming for a total of 30-60 mL/kg over the first few hours
* **Target Correction Rate:** The total rise in serum sodium should ideally not exceed 4-6 mEq/L in the first 24 hours, and not more than 8-10 mEq/L in the first 48 hours
* **Continuous Infusion:** After the initial bolus, a continuous infusion of 3% saline may be used to achieve the target correction rate
The rate is calculated based on the desired increase in sodium
A common approach for a 5 mEq/L rise in 24 hours might involve an infusion rate of approximately 0.5-1 mL/kg/hr of 3% saline, adjusted based on frequent sodium monitoring
* **Monitoring:** Serum sodium levels must be monitored very frequently, typically every 1-2 hours initially, then every 4-6 hours, and then daily as the patient stabilizes
This is paramount to prevent overcorrection and ODS
* **Underlying Cause Management:** Address the root cause of hyponatremia (e.g., fluid restriction for SIADH, addressing vomiting/diarrhea, managing endocrine disorders)
Avoid hypotonic fluids.
Surgical Management:
Surgical management is generally not indicated for hyponatremic seizures
Its role would be limited to addressing any underlying structural intracranial pathology that might be contributing to seizures or increased intracranial pressure, which would be identified on imaging.
Supportive Care:
Continuous cardiac and neurological monitoring
Maintain adequate airway and breathing
Monitor fluid balance and urine output closely
Nutritional support as tolerated
Close collaboration with neurology and critical care teams
Patient and family education regarding the condition and management plan.
Complications
Early Complications:
Osmotic demyelination syndrome (ODS), characterized by neurological deficits such as dysarthria, dysphagia, weakness, spasticity, and coma, particularly if sodium correction is too rapid
Seizure recurrence or status epilepticus
Worsening cerebral edema or herniation if hyponatremia is severe and not managed appropriately.
Late Complications:
Permanent neurological deficits, including cognitive impairment, motor deficits, and behavioral problems, if brain injury has occurred due to severe hyponatremia or its rapid correction.
Prevention Strategies:
Strict adherence to recommended sodium correction rates (avoiding rapid correction)
Frequent and accurate monitoring of serum sodium levels
Thorough assessment of the chronicity of hyponatremia before initiating treatment
Careful consideration of the underlying etiology of hyponatremia
Prompt identification and management of any contributing factors.
Prognosis
Factors Affecting Prognosis:
Severity and duration of hyponatremia
Rapidity of onset
Age of the patient
Presence of underlying neurological disease
Adequacy and timeliness of management
Development of osmotic demyelination syndrome.
Outcomes:
With prompt and appropriate management, most children can recover from hyponatremic seizures without lasting neurological sequelae
However, severe or prolonged hyponatremia, or rapid correction leading to ODS, can result in permanent disability.
Follow Up:
Long-term neurological and developmental follow-up is recommended for children who have experienced severe hyponatremic seizures, especially if there were complications
This includes monitoring for cognitive function, motor skills, and behavior.
Key Points
Exam Focus:
Hyponatremic seizures are a medical emergency
The primary treatment is cautious IV administration of 3% hypertonic saline
The rate of sodium correction is critical to prevent ODS
Monitor sodium levels very frequently
Aim for a rise of 4-6 mEq/L in the first 24 hours.
Clinical Pearls:
Always consider hyponatremia in a child presenting with seizures, especially if they are lethargic or have other non-specific symptoms
Differentiate between acute and chronic hyponatremia, as this dictates the urgency and rate of correction
Never correct hyponatremia too quickly
it's better to correct too slowly than too rapidly
The "rule of 6s" (6 mEq/L in 6 hours if acute/severe, 8-10 mEq/L in 24-48 hours for chronic) is a useful guide but requires frequent monitoring.
Common Mistakes:
Overcorrection of sodium leading to ODS
Inadequate monitoring of serum sodium levels
Using hypotonic fluids in hyponatremic patients
Delaying treatment in symptomatic hyponatremia
Misinterpreting urine electrolytes, leading to incorrect diagnosis of SIADH vs
other causes.