The child with polyuria and
polydipsia
Detlef Bockenhauer
Objectives
• To provide an overview of
polyuria/polydipsia by giving case
scenarios
• Aetiology
• Assessment
• management
?
Case 1: History
• A 6-month old boy is referred because of failure-tothrive and vomiting
• No other significant past or family history, born at
37 weeks gestation, normal pregnancy
Case 1: examination
• Unremarkable examination: weight: 5.54 kg
(<0.4th 5ile), height: 62.5 cm (>0.4th), OCF:
42.5 cm (<9th %ile)
• BP: 94 mmHg systolic
• Normal renal US
biochemistries Plasma
Urine
unit
Sodium
157
<5
mmol/l
creatinine
0.03
1.1
mmol/l
osmolality
319
83
mosmol/kg
Diagnosis?
• Diabetes insipidus (central or
nephrogenic)
Further investigations
• Admission for iv DDAVP test
• Max urine osm: 83 mosm/kg
Diagnosis?
• Nephrogenic diabetes insipidus
NDI: management
• Dietetic advice: restricting solute load to 15
mosm/kg/d but providing appropriate calories and
RDA for protein
• Each gram protein is metabolised to appr. 4 mmol of
urea
• Each gram of salt constitutes appr. 18 mosm (9
each for sodium and chloride)
• Lipids and carbohydrates do not generate solute
load (hence maxijul fortified milk)
NDI: medications
• Indometacin: enhances (?) proximal tubular
sodium uptake. NOT by chemical nephrectomy
• Thiazide: enhances proximal tubular sodium
uptake
• As PT is permeable for water, enhanced sodium
uptake results in enhanced water reabsoprtion,
thus less water is transported to CD, where it
cannot be reabsorbed.
• Medications can often be discontinued with
increasing age
Case 2: History
• A 3-year old boy is referred because of longstanding polyuria/polydipsia (since age 10 months)
• He drinks about 2.5 to 3 litres of fluid per day
• He gets up once or twice at night to drink
• Local assessment: normal growth and
biochemistries
• Water deprivation test (age 18 m): unable
(screams constantly for water)
• After DDAVP: generalised convulsion with Na of
125 mmol/l. Max urine osm: 482 msom/kg
• No significant past or family history
Case 2: examination
• Unremarkable examination: weight, height,
OCF: all around 9th %ile
• BP: 100/52 mmHg
• Normal renal US
biochemistries Plasma
Urine
unit
Sodium
141
15
mmol/l
creatinine
0.03
2.5
mmol/l
osmolality
288
55
mosmol/kg
Diagnosis?
• (partial) Diabetes insipidus (central or
nephrogenic) based on max Uosm of 482
• Habitual polydipsia
Further investigations
• Admission for water deprivation /iv DDAVP
test
• Max urine osm: 630 mosm/kg (normal
plasma Na throughout), 639 mosm/kg after
DDAVP
Diagnosis?
• ?(partial) Diabetes insipidus (central or
nephrogenic)
• Habitual polydipsia
Case 2: discussion
• not documented normal urine concentrating capacity
(>800 mosm/kg) ?washout
• Urine osmolality on spot samples always well below
(<100 mosm/kg) documented concentrating capacity
(>600 mosm/kg)
• Assuming an osmol load of 20 mosm/kg, urine
output with urine of 600 mosm/kg in a 20 kg child
would be 0.67 litres/day
• Polyuria thus likely secondary to polydipsia
• Hyponatraemic seizure during DDAVP highly
suspicious of habitual polydipsia
Case 3
• An 8-month old boy with excess polyuria and
polydipsia from newborn period (1200 ml/d)
• Normal growth, normal feeding
• DDAVP test at age 11-month (1 mcg IM
injection):
Urine Osmolality baseline 101
maximum 254
biochemistries Plasma
Urine
unit
Sodium
141
15
mmol/l
creatinine
0.03
2.5
mmol/l
osmolality
288
55
mosmol/kg
Diagnosis?
• Nephrogenic diabetes insipidus
• Treated with Indometacin and thiazide
• “Presentation is unusually mild”
Family history of polyuria & polydipsia
I1
II1
III1
II8
II4
III10
III13
Mother,III13:
Grandmother,II8:
Maternal uncle,III1:
Maternal uncle,III10:
Maternal g’aunt II1:
Maternal g’aunt II4:
Maternal g’grandfather I1:
Nephron Physiol 114(1), p1-p10
insulin dependent diabetes mellitus
“cranial” DI
nephrogenic DI
nephrogenic DI
nephrogenic DI
nephrogenic DI
history of severe polyuria
Case 3 continued
• Aged 5y, remained very well
• Treated with Indometacin and
bendroflumethiazide
• Excellent growth Ht 75th, Wt 25th centiles
• Normal plasma biochemistry
• Never admitted
IV1: repeat DDAVP test: 2mcg IM
Blood
Baseline
20mins
2h
3h
4h
5h
Na
142
141
Osm
291
289
Urine
Na
14
38
62
76
61
43
Osm
117
232
370
416
570
280
Mutation analysis
tested
x
x


  
All tested carry a mutation in AVPR2 : V88M
Diagnosis?
• Partial NDI
• Now treated with desmopressin at night
Case 4: Bartter
• A 4-months old ex-26 wk premie is
referred because of persistent polyuria (up
to 12 ml/kg/h) and intermittent
hypernatraemia
History
• Parents are first cousins, mother 24 y
old primigravida
• History of maternal polyhydramnion and
s/p 2 amnioreductions
biochemistries Plasma
Urine
unit
Sodium
157
45
mmol/l
creatinine
0.047
0.9
mmol/l
osmolality
318
197
mosmol/kg
Diagnosis?
Bartter Syndrome
Treatment of Bartter Syndrome
• COX-inhibitors
• Salt and potassium supplementation
Surprise!
Indomethacin (1 mg/kg/d) was started
Chemistries the next day as follows:
Na
K
Cl
HCO3
Osmolality:
150
4.8
119
21
311
mmol/l
mmol/l
mmol/l
mmol/l
mosm/kg
Urine Na:
Urine osmolality:
<5
76
mmol/l
mosm/kg
A case of Diabetes Insipidus?
DDAVP 0.05 mcg im was given.
Chemistries 4 hours later:
Na
Osmolality
Urine Na
140
290
7
Urine osmolality 63
mmol/l
mosm/kg
mmol/l
mosm/kg
Bartter?
Off Indomethacin - Bartter
Na
159
K
2.9
HCO3
24
Urine Na
Urine osmolality
82
253
or
DI?
Back on Indomethacin - DI
Na
142
K
4.8
HCO3
20
Osmolality
299
Urine Na
5
Urine osmolality
76
Discussion case 4
• Bartter syndrome classically associated
with isosthenuria
• About 20% of cases (Bartter 1 and 2) have
hyposthenuria (NDI)
• Mechanism unclear (hypercalciuria?)
• Treatment quandary: to give or not to give
salt
Polyuria: causes
Non-renal
• Excess water intake
• Increased solute load (DKA, mannitol)
Renal
• Impaired water reabsorption in CD (NDI)
• Impaired concentration gradient (Bartter,
NPHP, TIN)
conclusions
• Polyuria can be water (NDI, polydipsia) or solute
driven (Bartter, DKA, Mannitol etc.)
• Urine osmolality can help in assessment:
(Uosm<Posm in water diuresis;
Uosm≥Posm in solute diuresis)
• Clear distinction not always possible (e.g.
secondary NDI in Bartter)
• Maximal Uosm can be impaired in Habitual
polydipsia (“medullary washout”)
• Careful observation mandatory during DDAVP
test