A two year-old boy was admitted to the Emergency Department
after having a witnessed tonic clonic seizure lasting for less than 5 minutes
at home. The child is normally fit and well with no previous history of febrile
or afebrile seizure or family history of epilepsy. Prior to the seizure, there
were no respiratory or coryzal symptoms. No definitive history eliciting head
trauma was mentioned. However, the parent noticed that he had been drinking excessively
(estimated 2e3 litres) throughout the course of the day.
On examination, the child was post-ictal, drowsy and
lethargic. There was no rash. The rest of his examination was unremarkable. His
blood results showed a sodium level of 125 mmol/litres with normal renal function.
He was fluid restricted and observed overnight. His sodium levels normalized to
135 mmol/litres with good recovery. He was referred to the Endocrinology team for
follow up.
1. The child had a hyponatraemic seizure. Which ONE of the following conditions does NOT cause low serum sodium levels?
a. Syndrome of Inappropriate Antidiuretic Hormone
Secretion (SIADH).
b. Diabetes Insipidus
c. Diarrhoea
d. Hypertriglyceridaemia
e. Cirrhosis
2. Which ONE of the following statements in regards to hyponatraemia is false?
a. In hospitalized children, hypotonic fluid use for maintenance hydration is potential risk factor.
b. Acute hyponatraemia can cause brain cell swelling and cerebral oedema.
c. The emergency treatment of hyponatraemia is fluid restriction and 0.9% sodium chloride solution.
d. The recommended rate of correcting low sodium levels should not be faster than 10 mmol/litres a day.
e. In the treatment of SIADH, Intravenous furosemide may be needed.
3. Select ONE true answer about SIADH
a. Urine osmolality is usually low
b. Urine sodium can be high
c. Serum osmolality is high
d. Occurs commonly with nephrotic syndrome
e. SIADH does not cause hyponatraemia
Answers :
(1. b, 2. c, 3. b).
Hyponatraemia is a serum sodium level less than 135 mmol/litres. The causes of hyponatraemia can be classified according to the patient’s volume status:
1) Hypovolaemic hyponatraemia (seen in diarrhoea secondary to gastroenteritis or cerebral salt wasting
syndrome).
2) Hypervolaemic hyponatraemia (seen in congestive heart failure, cirrhosis or nephrotic syndrome).
3) Normovolaemic hyponatraemia (seen in SIADH or water intoxication).
Pseudohyponatraemia is a laboratory artefact that presents
when the plasma contains very high concentrations of protein (Multiple myeloma)
or lipid (hypertriglycerideamia).
The treatment of hyponatraemia is based on the specific aetiology. However, it is important to avoid overly rapid correction that might lead to central pontine myelinolysis or osmotic demyelination syndrome. The current recommendation, according to the British National Formulary (BNF),
is to correct sodium levels by a rate not faster than 10 mmol/litres in 24 hours. However, acute hyponatraemia with severe neurological symptoms, requires urgent correction of sodium levels in order to reduce the incidence of cerebral oedema. Intravenous hypertonic saline (4e6
ml/kg of 3% sodium chloride) is the recommended treatment. Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is characterized by hyponatraemia, inappropriately concentrated urine, high urine osmolality, low plasma osmolality and normal-to-high urine sodium. It
is an uncommon condition in children. It can be caused by CNS disorders (trauma, infection, tumour, haemorrhage), pneumonia, hypothalamic-pituitary surgery and excessive administration of Vasopressin in the treatment of Diabetes Insipidus. Drugs, such as Carbamazepine and some tricyclic
antidepressants can increase vasopressin secretion or mimic vasopressin action. The recommended treatment is fluid restriction, usually to two-thirds of oral intake or less and diuresis to remove excessive free water.
The treatment of hyponatraemia is based on the specific aetiology. However, it is important to avoid overly rapid correction that might lead to central pontine myelinolysis or osmotic demyelination syndrome. The current recommendation, according to the British National Formulary (BNF),
is to correct sodium levels by a rate not faster than 10 mmol/litres in 24 hours. However, acute hyponatraemia with severe neurological symptoms, requires urgent correction of sodium levels in order to reduce the incidence of cerebral oedema. Intravenous hypertonic saline (4e6
ml/kg of 3% sodium chloride) is the recommended treatment. Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is characterized by hyponatraemia, inappropriately concentrated urine, high urine osmolality, low plasma osmolality and normal-to-high urine sodium. It
is an uncommon condition in children. It can be caused by CNS disorders (trauma, infection, tumour, haemorrhage), pneumonia, hypothalamic-pituitary surgery and excessive administration of Vasopressin in the treatment of Diabetes Insipidus. Drugs, such as Carbamazepine and some tricyclic
antidepressants can increase vasopressin secretion or mimic vasopressin action. The recommended treatment is fluid restriction, usually to two-thirds of oral intake or less and diuresis to remove excessive free water.
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