Polyuria, Polydipsia and Possible Diabetes Insipidus?

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Patient Presentation
A 20-month-old male who had just moved to the area came to clinic with a history of several months of polyuria and polydipsia. He demanded to drink all the time and would gulp 4+ ounces at a time and didn’t care what type of fluid it was. He would seek out other fluid such as drinking from water hoses and pet water bowls if he was denied fluid. His mother described 20-25 diapers/day that would be soaked with urine. At night the mother would set up several bottles of fluid for the boy and would need to change his diaper several times which disrupted their sleep. He was otherwise well and had normal growth and development when his medical records were reviewed.

The past medical history showed a full term infant with no trauma, significant illnesses, hospitalizations or surgery. The family history was negative for any early childhood illnesses or deaths. The mother denied any central nervous system, endocrine or kidney problems. Most people in the family died of heart disease or stroke. The review of systems was negative including any fevers, weight or growth problems, sleep, or elimination.

The pertinent physical exam showed normal growth in a happy playful child who drank 4 ounces of fluid and had 2 wet diapers during the visit. There were no obvious midline defects including no hypertelorism, high arched palate etc. Heart revealed no abnormal sounds or rhythms. Abdominal and genitourinary systems were normal.

The diagnosis of ongoing probable polyuria and polydipsia was made. The laboratory evaluation included a normal basic metabolic panel, glucose and hemoglobin A1c, calcium and thyroid tests. The urinalysis showed a specific gravity of 1.060, pH of 7 and was otherwise normal. Urine osmolality was 162 mOsm/L and spot urine sodium was 24 mEq/L. Given the fluid seeking behaviors, normal physical examination and laboratory findings, the diagnosis of diabetes insipidus versus a primary polydipsia was strongly considered. During a telephone consultation, the endocrinologist agreed with the general pediatrician and the patient was scheduled to be seen with a water deprivation test at that time.

Discussion
The body is smart. It has mechanisms for maintaining balances within the body in a closely controlled manner but allows for a variety of states. This is very true for fluid balance in the body which is highly controlled between almost all of the major body organ systems. When fluid is low, the sensor sends signals for us to drink, and conserves fluid until we can. When the fluid is high, the kidneys excrete the excess and sends signals not to drink. Usually it works very well. While there are many pathological states that can cause polyuria and/or polydipsia, the most common reason is excessive fluid intake because of habit or behavioral causes.

Polyuria is an excessive production of urine. Normal urination varies by age and decreases as the kidneys mature. Polyuria needs to be distinguished from frequent toileting, nocturia and enuresis, and just plain urinary frequency. Anatomic abnormalities such as meatal stenosis, posterior urethral valves, or labial adhesions may also appear to cause frequent urination. Additionally, some normal fluids such as caffeine can have a short term diuretic effect.

Normal urine volume is:

  • Birth – 150 ml/kg/day
  • 2 years – 100-110 ml/kg/day
  • 2 years 40-50 ml/kg/day

Causes of polyuria include:

  • Fluid excess
    • Polydipsia
    • Intravenous fluid overadministration
  • Diabetes mellitus and hyperglycemia
  • Diabetes insipidus
  • Diuretics
  • Electrolyte abnormalities
    • Hypercalcemia
  • Nocturnal polyuria
    • Enuresis

Confirmation of polyuria can usually be accomplished by a 24-hour urine collection. For diapered children, weights of diapers before and after use can give the volume.

Polydipsia is excessive thirst which causes consumption of larger than normal volumes of fluid.
Polydipsia needs to be distinguished from habitual drinking or fluid preferences.
Normal fluid intake is usually calculated by the child’s weight:

  • 0-10 kg = 100 ml/kg
  • 10-20 kg = 1000 ml + 50 ml/kg
  • > 20 kg = 1500 ml + 20 ml/kg

Note that the amount of fluid intake is also dependent on environmental temperature and physical activity.
Fluid intake will necessarily exceed fluid out because of incessant losses.

Causes of polydipsia include:

  • Inadequate intake or dehydrated state
  • Diabetes mellitus and hyperglycemia
  • Diabetes insipidus
  • Excessive exercise
  • Excessive water drinking as it causes increased fluid output

With true polydipsia, patients will have an insatiable thirst and will seek fluid wherever they can if denied access to usual sources. These would include drinking from pet bowls, toilet bowls, mop heads, water hoses, etc. These behaviors can cause risks of water intoxication and also safety risks for drinking inappropriate fluids such as bleach, coolants, etc. Confirmation of polydipsia usually can be accomplished by a diary of fluid intake and type of fluid.

A differential diagnosis of presentation of polyuria and/or polydipsia includes:

  • Excessive water drinking
  • Central nervous system
    • Head trauma
    • Neurosurgery
  • Electrolyte abnormalities
    • Hypercalcemia
    • Hypokalemia
  • Endocrine
    • Diabetes mellitus
    • Diabetes insipidus
    • Adrenal insufficiency
    • Congenital adrenal insufficiency
    • Cushing’s
    • Renal tubular acidosis, Type 4
  • Genetic/congenital
    • Familial
    • Kabuki syndrome
    • Septo-optic dysplasia
  • Iatrogenic
    • Intravenous fluid overadministration
    • Diuretic medication
    • Other drugs
  • Infection
    • Urinary tract infection
    • Meningitis/encephalitis causing central diabetes insipidus
  • Renal
    • Polycystic kidney disease
    • Sickle cell nephropathy
    • Renal tubular acidosis (Bartter or Gitelman syndromes)
    • Renal failure
  • Tumor/infiltrative
    • Catecholamine secreting tumor
    • Craniopharngioma
    • Germinoma
    • Histiocytosis
    • Pituitary adenoma
    • Sarcoidosis
  • Other
    • Malnutrition

Baseline evaluation for polyuria/polydipsia often includes:

  • Urinalysis
  • Urine sodium and osmolality
  • Urine glucose
  • Basic metabolic panel
  • Calcium
  • Glucose
  • Other possibilities include cortisol, thyroid function tests

Learning Point
Diabetes insipidus (DI) is a syndrome where there is chronic excretion of excessive amounts of dilute urine. Diagnosis is made using measurements of 24-hour urine volume, osmolality, and glucose and sodium values. Additional testing including water deprivation testing and desmopressin testing may be necessary. Vasopressin, copeptin levels and magnetic resonance imaging of the head may also be employed. Specialized testing should be performed by appropriate specialists because of the potential risks involved with these tests in addition to necessary lab conditions and cost. In DI, the urine volume is high, urine osmolality is low, urine glucose is negative, urine specific gravity and sodium will vary depending on conditions. It is also important to remember that the vasopressin levels or insensitivity to them may be partial and not absolute. Therefore some of the presenting symptoms or laboratory values can vary.

There are 4 types of DI

  • Central or pituitary DI
    • Caused by inadequate vasopression production or secretion by the pituitary gland
    • Causes include
      • Genetic/congenital – autosomal dominant, recess or X-linked recessive, holoproencephaly
      • Acquired – problems that destroy or invade the pituitary such as trauma, neoplasms, infections, CNS vascular problems
    • Treatment is desmopressin, vasopressin
  • Nephrogenic DI
    • Caused by renal insensitivity to vasopressin
    • Causes include
      • Genetic – autosomal dominant, recessive or X-linked recessive
      • Acquired – problems that change the renal function such as drugs, electrolyte abnormalities (hypercalcemia, hypokalemia), neoplasms, renal vascular problems
    • Treatment is diuretics and/or indomethacin
  • Primary polydipsia
    • Abnormal thirst (dipsogenic) or abnormal cognition (psychogenic) causes an increased secretion of vasopression
    • Treatment is environmental changes, education and potentially psychotherapy
  • Gestational DI
    • Increased degradation by the placenta of vasopression during pregnancy
    • Usually begins in 3-4 month of gestation and resolves within 4-6 weeks after delivery
    • Treatment if needed is desmopressin

Questions for Further Discussion
1. How does diabetes mellitus present?
2. What causes urinary frequency?
3. What causes syndrome of inappropriate antidiuretic hormone? A review can be found here

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Diabetes Insipidus

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Robertson GL. Diabetes insipidus: Differential diagnosis and management. Best Practice & Research Clinical Endocrinology & Metabolism. 2016;30(2):205-218. doi:10.1016/j.beem.2016.02.007

Mahon M, Amaechi G, Slattery F, Sheridan AL, Roche EF. Fifteen-minute consultation: Polydipsia, polyuria or both. Arch Dis Child Educ Pract Ed. 2019;104(3):141-145. doi:10.1136/archdischild-2018-315486

Kavanagh C, Uy NS. Nephrogenic Diabetes Insipidus. Pediatric Clinics of North America. 2019;66(1):227-234. doi:10.1016/j.pcl.2018.09.006

Patti G, Ibba A, Morana G, et al. Central diabetes insipidus in children: Diagnosis and management. Best Pract Res Clin Endocrinol Metab. 2020;34(5):101440. doi:10.1016/j.beem.2020.101440

Author
Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa

Published