Abstract
Primary polydipsia (PP) is a rare but significant clinical entity in pediatric patients. Here, we present the case of a 16-month-old female referred to our center due to recurrent episodes of electrolyte imbalances. Initially admitted for management of a viral illness, she experienced unexplained electrolyte disturbances, prompting subsequent admissions marked by similar disruptions. Despite stabilization and discharge, her condition persisted. Pre-referral laboratory findings revealed significant electrolyte abnormalities alongside polyuria symptoms. Investigations unveiled a history of frequent heavy wet diapers and increased thirst. Further tests including a water deprivation test excluded diabetes insipidus. Following the restriction of water intake and careful monitoring, her condition markedly improved. This case emphasizes the importance of thorough evaluation in persistent electrolyte imbalances in toddlers, highlighting the role of polyuria as a contributing factor and the efficacy of targeted interventions in managing such cases.
Introduction
Primary polydipsia (PP) is a disorder of urine concentration due to excessive water consumption. This leads to an increased output of a dilute and hypotonic urine.1 If not managed properly, PP would lead to imbalances in serum electrolytes, particularly hyponatremia.1 PP can be classified according to cause, such as psychogenic polydipsia and dipsogenic polydipsia.2 Psychogenic polydipsia is usually associated with psychiatric diseases such as schizophrenia, whereas dipsogenic polydipsia may stem from habitual overconsumption of water or, more seriously, from an impairment in the hypothalamic thirst center.1,2 The prevalence of PP among toddlers is not clearly established. In this context, we present a case involving a 16-month-old female, who exhibited symptoms of excessive urination and electrolyte imbalances. Following investigations, the diagnosis of PP was confirmed.
Case Presentation
A 16-month-old female was referred to our center for evaluation of persistent electrolyte imbalances. Initially, she was admitted following the incidental discovery of abnormal electrolyte levels during management for a viral illness. According to the referral center, the patient exhibited laboratory findings consistent with unexplained hypokalemia with serum values of 2.9 mEq/L and hyponatremia (130 mEq/L). She was managed in the hospital, and her electrolyte levels were stabilized before discharge. Follow-up after 3 days showed another incident of hyponatremia (128 mEq/L); however, potassium levels were normal (3.8 mEq/L). At the referral center, arterial blood gas (ABG) sampling showed a pH of 7.42, bicarbonate level of 14.9 mmol/L, and a normal anion gap of 12. She was admitted once again to the hospital and given appropriate management for hyponatremia. Subsequently, she was referred to our pediatric nephrology department for investigation of unexplained electrolyte disturbances.
The patient was born at 38 weeks of gestation following an uncomplicated pregnancy and delivery, with a birth weight of 3.3 kg (−0.93 SD), a length of 49 cm (−1.16 SD), and a head circumference of 34 cm (−1.41 SD). Past medical history and family history were unremarkable.
She presented to our center with a weight of 6.4 kg (−5.4 SD), length of 68 cm (−3.35 SD), and a head circumference of 41 cm (−4.02 SD). Growth parameters were not followed up with routine well-child visits. Developmental milestones were normal in terms of fine motor skills, language, and cognition. Gross motor skills were slightly delayed, with the child beginning to walk independently at the age of 14 months. On examination, the child looked well and was vitally stable. Systemic examination did not reveal any abnormalities. She was tolerating oral feeding throughout her hospital stay. At referral, she was receiving oral potassium (1200 mg twice daily), oral bicarbonate (5 mL twice daily), and oral NaCl 0.9% (5 mL twice daily). This management was stopped upon arrival at our center, as there was no evidence of unstable electrolyte imbalance.
Upon taking further history from the child’s mother, she elaborated that her child drinks several bottles of water per day. The child often seems distressed throughout the day but calms down when given a bottle of water. She was breastfed until 3 months of age, when her mother started giving regular milk formulas. She started eating solid food at the age of 6 months; however, she often refused milk and food, preferring water instead. Upon further investigation at our center, the patient’s mother reported a significant history of frequent, heavy wet diapers (more than 8 times per day). Baseline laboratory tests at the time of admission are interpreted in Table 1.
Laboratory Findings Before and After the Water Deprivation Test.
A 24-hour urine collection returned a urine volume of 2350 mL (15 mL/kg/h), consistent with polyuria. Further tests revealed a low serum osmolality and a low-normal urine osmolality. Urine analysis showed dilute urine, and urine culture results were negative. A renal ultrasound showed mild dilation in the lower calyces of the left kidney; otherwise, both kidneys were normal in size, shape, and echogenicity. An abdominal and chest computed tomography (CT) scan were unremarkable.
A water deprivation test was conducted for 3 hours to exclude diabetes insipidus (DI), and the results are outlined in Table 1. Following the water deprivation test, urine osmolality significantly increased. Serum sodium, potassium, chloride, calcium, and phosphate were within the normal range. Kidney function tests were also normal. Arterial pH measured 7.4, bicarbonate 21.4 mmol/L, and a normal anion gap.
Following the notable improvement of her laboratory results after the water deprivation test, the patient’s water intake was restricted to 1 L per day. Owing to failure to thrive, caloric intake was increased using specially formulated nutritional supplements giving 2 servings per day, each serving has a volume of 220 mL, containing 240 kcal, with 1 mL of Medium- Chain Triglycerid (MCT) oil added to each 100 mL. We also ensured that the child was eating solid food regularly. Her weight before discharge was measured to be 7.23 kg, indicating adequate weight gain in conjunction with the increased caloric intake. The cause of failure to thrive was attributed to malnutrition due to the child’s refusal to eat, preferring to drink water.
On her last day of admission, urine volume showed a collection of 900 mL (5.8 mL/kg), indicating a resolution of her polyuria. With the findings interpreted by the water deprivation test, DI was excluded, and psychogenic polydipsia was confirmed as the cause of the child’s electrolyte imbalances and polyuria. As the water deprivation test conclusively diagnosed PP, a brain magnetic resonance imaging (MRI) was not performed. At discharge, her laboratory values showed normal serum electrolytes, normal serum and urine osmolality, and normal urine analysis as interpreted in Table 1.
The patient returned 1 week after discharge for a follow-up examination. Laboratory tests showed normal sodium (143 mEq/L) and normal potassium levels (4.1 mEq/L). She was compliant with her increased caloric intake and water restriction. Symptoms of polyuria had resolved, and the number of wet diapers per day had decreased to 4 to 5. Examination of developmental milestones remained normal. Follow-up on growth parameters showed an increase in her weight from 7.23 kg at discharge to 7.6 kg, indicating continued adequate weight gain. She was recommended to follow up on her nutritional status with her pediatrician and to record growth parameters to ensure that she is growing adequately.
Discussion
The case report discusses PP—a disorder of water homeostasis that is characterized by excessive fluid intake. It results in an increased production of a dilute urine that exceeds 3 L/d in adults and 2 L/m2/d in children, fitting the definition of polyuria.3 Although PP is frequently observed in adolescents and adults, its occurrence in toddlers is less documented. Our report presents a case of a toddler exhibiting unexplained electrolyte imbalances upon laboratory examination, ultimately diagnosed with PP.
The physiology of water homeostasis is regulated by the hormone arginine vasopressin (AVP) (also known as antidiuretic hormone [ADH]).4 The AVP is released from the posterior pituitary gland when the serum osmolality exceeds a certain threshold, typically above 280 mOsm/kg.4 It functions by binding to vasopressin-2 receptors on the renal collecting tubules, promoting water reabsorption. In cases of PP, excessive water consumption results in a decrease in serum osmolality, inhibiting AVP release and leading to the production of large volumes of hypotonic urine.4 Thirst serves as a crucial mechanism for maintaining water balance, as the thirst centers are stimulated by increased serum osmolality, prompting water intake.4 Thirst is usually satiable by consuming enough water to return serum osmolality to its normal range. However, individuals with PP consume water excessively to an unquenchable extent. The pathophysiology of this phenomenon is poorly understood and remains unclear.2
The PP is classified into dipsogenic polydipsia and psychogenic polydipsia. The latter is mainly associated with psychiatric conditions such as schizophrenia.1 Research suggests that individuals with schizophrenia may have central defects impacting thirst centers and dysregulation of AVP secretion.2 Other psychiatric conditions associated with psychogenic polydipsia include anxiety disorders, depression, dependency disorders, and anorexia nervosa.2 Dipsogenic polydipsia, on the contrary, can stem from somatic factors, potentially resulting from damage to the thirst centers. Common causes include cerebral lesions, vascular issues, granulomatous diseases, and infectious diseases.2 Lifestyle also plays a role in predisposing individuals to dipsogenic polydipsia, often termed habitual polydipsia. This condition is observed in healthy individuals who habitually consume excessive amounts of water, such as performance athletes.2
Diagnosing PP in infants and toddlers is rare and presents a challenge due to the often inconclusive primary symptoms, which rarely suggest a water imbalance disorder. Electrolyte disturbances are typically incidental, as clinical signs of hyponatremia usually manifest when serum sodium concentration drops to 120 mEq/L.5 Unlike in adults, where PP cases often stem from psychogenic behavior, such behavior cannot be anticipated in infants and toddlers. However, reports indicate that PP can occur in children experiencing home disturbances and neglect.6 Some cases have even been described as a form of child abuse, involving forceful water ingestion.6
In our case, the child was referred from primary care due to an incidental discovery of unexplained electrolyte disturbances (hyponatremia and hypokalemia). After addressing the electrolyte imbalances, the patient was transferred to pediatric nephrology for further evaluation. A comprehensive history and physical examination revealed that the child was experiencing polyuria, necessitating diaper changes more than 8 times a day, with predominantly wet diapers. Inquiry into the child’s fluid intake was inconclusive regarding the exact amount, but the mother mentioned that they frequently offered water to soothe the child when distressed, which later became a habit leading to excessive water consumption. Several studies have described excessive water drinking in infants and children in a form of attachment to the bottle, where parents often offer it as a first response to distress. When given the bottle, the child quickly calms down, but the caretaker interprets this as a sign of thirst, perpetuating the cycle.5,7
When suspecting PP, it is crucial to exclude other potential diagnoses listed in the differential of polyuria. Central and nephrogenic DIs are particularly important conditions to investigate when considering a water imbalance disorder.5 Another significant condition to consider is diabetes mellitus (DM).5
To eliminate other potential suspicions, a thorough medical history should be obtained from the patient, alongside laboratory investigations including serum and urine electrolyte levels, serum and urine osmolality, 24-hour urine volume measurement, and imaging studies such as brain CT or MRI.1
The initial step involves assessing urine osmolality. If the osmolality measures <800 mOsm/kg, the next focus shifts to serum sodium levels.1 A serum sodium level below 135 mEq/L strongly suggests PP. However, if serum sodium levels range between 135 and 147 mEq/L, a water deprivation test is recommended.1 In the case at hand, the child exhibited low urine osmolality (56 mOsm/kg) and a serum sodium level of 135 mEq/L, prompting the continuation of investigations with a 3-hour water deprivation test. During this test, the child’s water intake was restricted, and cardiac monitoring was initiated. Subsequently, following deprivation, there was a notable increase in urine osmolality to 234 mOsm/kg and serum sodium to 143 mEq/L. As part of management, water restriction to 1 L was maintained throughout the hospital stay.
Typically, urine osmolality rises to >800 mOsm/kg after a water deprivation test, but this often requires a longer duration (usually overnight or >8 hours).1 However, in this instance, a significant elevation in urine osmolality (from 56 to 234 mOsm/kg) was observed over a 3-hour water deprivation period, markedly heightening suspicion of PP over DI. Another crucial aspect evaluated during a water deprivation test is the resolution of polyuria. Initially, the child exhibited polyuria, as evidenced by a 24-hour urine collection yielding a volume of 2350 mL (15 mL/kg/h), which exceeds the typical urine output for a toddler (approximately 4 mL/kg/h).8 However, following water deprivation and subsequent fluid restriction, the urine output decreased to 900 mL (5.8 mL/kg/h) by the last day of admission. The reduction in polyuria typically helps differentiate between PP and DI, in conjunction with urine osmolality readings.6
An essential aspect of managing PP in children involves addressing the electrolyte imbalances and preventing the risk of water intoxication. Although water intoxication is rare in children due to their effective fluid regulation mechanisms, it remains crucial to monitor and manage any electrolyte imbalances, particularly hyponatremia.6 The sole management of PP is to prevent its occurrence, often by addressing the habit of excessive water consumption. Early intervention is key, as it is more effective in curbing excessive drinking habits, which can be challenging to address, especially when children have become attached to their water bottles.5 Decreasing water intake should be approached gradually to minimize any distress or irritability in children adjusting to the change.5
Conclusion
It is crucial to recognize PP as a potential diagnosis in toddlers experiencing polyuria, and polydipsia, along with unexplained electrolyte disturbances. The prevalence of PP in this age group may be higher than reported due to the reluctance of pediatricians to associate compulsive drinking behavior with nonpsychotic children. It is essential to exclude other potential causes before suspecting PP. Employing several investigative methods and tests such as a water deprivation helps differentiate PP from DI. Following the diagnosis of PP, it is crucial to maintain fluid balance and prevent the complications of water intoxication.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Ethics approval
Our institution does not require ethical approval for reporting individual cases or case series.
Informed consent
Written informed consent was obtained from a legally authorized representative(s) for anonymized patient information to be published in this article.
