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A diagnostic dilemma

When a child has an increased thirst or produces large quantities of dilute urine there are key questions to be asked during history taking in the emergency department.

When a child has an increased thirst or produces large quantities of dilute urine there are key questions to be asked during history taking in the emergency department.

Polyuria dilemma
It is important ED nurses remain aware of diagnoses in polyuria and polydipsia. Picture: Alamy

When a child presents with polyuria and polydipsia, diabetes mellitus – due to insulin deficiency – is often considered first. Conditions such as diabetes insipidus (DI) and habitual polydipsia (HP) may present similarly but with normal blood glucose levels.

It is, therefore, important that emergency department (ED) nurses and other professionals remain aware of these diagnoses. If they do not there is a risk of inappropriately discharging children believing increased thirst is due to environmental factors.

Hormone deficiency

DI is caused by a deficiency of anti-diuretic hormone (ADH) production from the posterior pituitary gland (cranial DI), or an inadequate renal response to normal levels of ADH (nephrogenic DI). It can be associated with abnormalities such as septo-optic dysplasia or craniopharyngioma, or acquired following severe head trauma, certain brain tumours, tuberculosis or meningitis (Davies and Collin, 2015; Dabrowski et al 2016).

ADH regulates reabsorption of water into the cardiovascular system, reduced levels manifest as polyuria and polydipsia and the ability to concentrate urine is decreased (Davies and Collin, 2015). If left untreated, DI can lead to brain damage, impaired mental function, intellectual disability, hyperactivity, short attention span, and/or restlessness.  

Diagnosing DI

Children with DI have an excessive and often insatiable thirst and prefer cold water. If they can’t find a drink, they may drink water from inappropriate sources such as toilets, sinks or drain pipes (Dabrowski et al 2016). These children tend to wake up for drinks and may have multiple episodes of small patches of nocturnal enuresis.

DI should also be considered as a differential diagnosis in older children with secondary enuresis. Treatment of DI is managed by specialists, and pharmacological agents such as desmopressin and thiazide diuretics are used.

Monitoring and management

Another condition which can mimic DI is HP where children drink large volumes of fluids such as juice and squash without a physiological stimulus. It is relatively common in young children and may reflect poor parental understanding of fluid volumes needed for children of various ages. These children can tolerate thirst, wait for drinks to be provided and do not usually wake up at night for drinks.

There is generally one big episode of enuresis early in the night. The management of HP is based on fluid restriction and monitoring.

At initial triage, once the blood glucose is found to be normal, it is essential to obtain an accurate history of the presenting symptoms.

It is important to ask:

  • Does the child access drinks from inappropriate places?
  • Does the child wake up for drinks in the night?
  • How many times does the child wet the bed?
  • Is there previous history of severe head injury, brain tumours or meningitis?
  • Does the child continue to pass urine when drinks are withheld? (seen in DI but not in HP.)

 

Specialist referral is necessary to diagnose and differentiate between the two conditions. A detailed history will help specialists to consider these diagnoses. Sodium levels should be done in the ED as HP is associated with hyponatraemia, while DI is more likely to exhibit high normal sodium levels or hypernatraemia. Diagnostic tests done by specialists include urine and blood investigations, water deprivation test and MRI for pituitary abnormalities.

Children with DI often present to the ED during inter-current illnesses. The child may not be able to drink enough to maintain water balance and can develop severe hypernatraemia. It is important that ED nurses triage these children as urgent and request a medical assessment immediately.  


References

Dabrowski E, Kadakia R, Zimmerman D (2016) Diabetes insipidus in infants and children. Best Practice and Research. Clinical Endocrinology and Metabolism. 30, 2, 317-328.

Davies K, Collin J (2015) Understanding clinical investigations in children’s endocrinology. Nursing Children and Young People. 27, 8, 26-37.


About the authors

Harriet Le Gresley is a fifth year medical student at Peninsula College of Medicine and Dentistry, Plymouth University.

Sarah Palmer is a paediatric sister in an emergency department at Yeovil District Hospital in Somerset.

Siba Prosad Paul is consultant paediatrician at Torbay Hospital, Torquay in Devon.

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