Hyponatremia natural history, complications and prognosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Saeedeh Kowsarnia M.D.[2]

Overview

If left untreated, [#]% of patients with [disease name] may progress to develop [manifestation 1], [manifestation 2], and [manifestation 3].

OR

Common complications of [disease name] include [complication 1], [complication 2], and [complication 3].

OR

Prognosis is generally excellent/good/poor, and the 1/5/10-year mortality/survival rate of patients with [disease name] is approximately [#]%.

Natural History, Complications, and Prognosis

Natural History

Serum sodium concentration is the main determinant of serum osmolality. Maintaining constant serum sodium and osmolality is essential for keeping cell volume stable. This maintenance is very crucial for brain cells and volume. In acute hyponatremia, an osmotic gradient between brain cells and serum, causing water to enter brain cells and increasing brain volume, edema, intracranial pressure and risk of herniation .In chronic hyponatremia, brain cells have time to lose osmoles (amino acids, polyols) to re-equilibrate the osmolar gradient and cell volume .

Complications

Hyponatremic Encephalopathy :Early symptoms of hyponatremia from any cause may include apathy, weakness, muscular cramps, nausea, vomiting, and headache. More advanced clinical manifestations include impaired response to verbal and painful stimuli, hallucinations, urinary incontinence, and pulmonary edema. As edema worsens, clinical manifestations of hyponatremia are related to the degree of increased intracranial pressure and brain herniation. These manifestations may include decorticate posturing, hypothermia and hyperthermia, central diabetes insipidus, seizures, respiratory arrest, coma, permanent brain damage, and death .Pulmonary edema in hyponatremiac encephalopathy named

Stage	Clinical manifestation of hyponatremic encephalopathy
Early	Anorexia, headache, nausea, vomiting, muscule cramps, weakness, confusion, altered consciousness, agitation, gait disturbances
Advanced	Impaired response to verbal stimuli, impaired response to painful stimuli, bizarre (inappropriate) behavior, hallucinations (auditory or visual), asterixis, obtundation, incontinence (urinary or fecal), respiratory insufficiency
Severe	Decorticate and/or decerebrate posturing, bradycardia, hyper- or hypotension, altered temperature regulation (hypo- or hyperthermia), anisocornea, papilledema, dilated pupils, seizure activity (usually grand mal), cardiac arrhythmias, myocardial ischemia, pulmonary edema, respiratory arrest, coma, polyuria (secondary to central diabetes insipidus)

Brain herniation :In acute hyponatremia, if the brain adaptation to hyponatremia is impaired especially solute excretion of brain cells to achieve osmotic equilibrium, it causes brain cells swelling, increased intracranial pressure, cerebral edema, and eventual tentorial herniation .

Osmotic Demyelination syndrome (Central Pontine Demyelination) :Hyponatremia, serum sodium < 135 mEq/L, causes brain edema due to shift of water from extracellular in to the brain cells. In the next 24 to 48 hours, brain starts to compensate by excreting solutes and water. If serum sodium is corrected too rapidly, brain cells do not have time to replace the solutes which results in dehydration of the brain cells named osmotic demyelination syndrome .

Signs and symptoms of ODS
Change in mental status Dysphagia Reduced attention span Loss of memory Rapid development of quadriparesis Dysarthria Reduced speed of processing information Ataxia and Parkinson-like symptoms

Risk of developing Osmotic Demyelination Syndrome is increased with:

• Serum sodium concentration ≤105 mmol/L
• Hypokalemia
• Alcoholism
• Malnutrition
• Advanced liver disease

Prognosis

• Asymptomatic hyponatremia in:
  • Adults is associated with attention and gait deficit, falls and fractures, and increased mortality in patients with pneumonia, heart failure and liver disease .
  • Preterm neonates is associated with poor development and growth, cerebral palsy, sensorineural hearing loss, and intracranial hemorrhage, increased perinatal mortality in neonates who suffered perinatal asphyxia and increased sodium intake in later life .