|
A 19-year-old girl, previously healthy, was admitted
because of increased frequency of urination and polydipsia.
She had been well until one month earlier when she had to wake
up at least twice every night to urinate. The symptoms became
more frequent with time and the frequency of urination during
the daytime also increased. Her urine seemed colorless and
clear. Thirsty sensation bothered her and she found herself
never without a beverage in her hand or nearby. On account of
the above symptoms, she was taken to our clinic by her mother
for further evaluation.
She denied having had head trauma, surgery, eating disorder
or use of other medication in the past. She did not drink
coffe or alchohol. There was no history of exposure to
contrast medium. There were no other members of the family who
had similar symptoms.
On examination, her consciousness was clear, height was 158
cm and her weight was 48 kg. The body temperature was 36.4°C,
pulse rate 89 beats per minute, the respirations 20 per
minutes and the blood pressure was 100/68 mmHg. The
conjunctivae were pink, sclerae were anicteric and the pupils
were isocoric with prompt light reflex. The neck was supple
without a goiter, palpable masses, engorged jugular veins or
lymphadenopathy. Chest, heart, abdomen and back were normal.
The extremities were freely movable without edema.
Neurological examinations were unremarkable.
A blood chemistry profile revealed a plasma sodium value of
143 mEq/L, plasma osmolarity of 308 mOsm/L, and fasting plasma
glucose of 86 mg/dl. Analysis of a urine specimen showed an
osmolarity of 89 mOsm/L; the urine specimen was negative for
the presence of glucose and whilte blood cells or casts. The
remaining renal function and other general laboratory survey
were normal.
After admission, recorded daily water intake and urine
amount was approximately 5 liters and 9 liters, respectively.
Water deprivation test was performed. After five hours of
fasting, her body weight decreased by 3%, and the test was
terminated. Plasma osmolariy increased to 315 mOsm/L and the
urine osmolarity was unchanged. Subsequently, intramuscular
injection of 2mg
desmopressin was given. One hour later, the plasma osmolarity
decreased to 290 mOsm/L and urine osmolarity increased to 425
mOsm/L (Table). Further magnetic resonance imaging (MRI) of
the brain disclosed no significant findings. Diagnosis of
central complete diabetes insipidus was made. Anterior
pituitary hormone levels were checked and showed no
abnormalities. The patient was put on desmopressin 10mg
every 8 hours administered via nasal inhalation daily. Her
polyuria and polydipsia improved after treatment while she
received regular follow-up at our hospital.
<Laboratory
data>
1.Results of baseline biochemistry
| Lab test |
BUN |
Cr |
Na |
K |
ALT |
T-bil |
Reference
value |
<24
mg/dL |
<1.3
mg/dL |
135-145
mmol/L |
3.5-5.3
mmol/L |
<37
U/L |
0.2-1.0
mg/dL |
| Test result |
32.5 |
0.7 |
143 |
3.5 |
29 |
0.3 |
2.Results of the anterior
pituitary hormone levels
| Lab test |
hsTSH |
FT4 |
ACTH |
Cortisol |
FSH |
LH |
Estradiol |
hGH |
Prolactin |
| Reference value |
0.4- 4 μIU/mL |
0.60-1.75 ng/dL |
10-65 pg/mL |
5-25 μg/dL |
3.5-10.5 mIU/mL |
1.5-8.3 mIU/mL |
13.6-36.8 pg/mL |
0.06-5 ng/mL |
1.4-24.2 ng/mL |
| Test result |
0.67 |
1.5 |
12 |
22 |
8.6 |
7.4 |
22.5 |
0.08 |
16.8 | ** Abbreviations: hsTSH,
high sensitivity thyroid-stimulating hormone; FT4, free
thyroxine; ACTH, corticotrophin; FSH, follicle-stimulating
hormone; LH, luteinizing hormone; hGH, growth
hormone.
3.Water deprivation
test
| Time |
Urine amount (ml) |
BW (kg) |
Urine specific gravity |
Urine osm (mosm/kg) |
Plasma osm (mosm/kg) |
Plasma Na(mEg/L) |
| 0 am |
390 |
48 |
1.002 |
85 |
306 |
142 |
| 1 am |
580 |
48 |
1.002 |
83 |
307 |
142 |
| 2 am |
495 |
47.6 |
1.002 |
86 |
307 |
143 |
| 3 am |
598 |
47.1 |
1.003 |
82 |
310 |
144 |
| 4 am |
610 |
46.9 |
1.003 |
79 |
313 |
144 |
| 5 am |
636 |
46.5 |
1.003 |
88 |
315 |
144 |
| 6 am |
90 |
46.8 |
1.013 |
425 |
290 |
141 |
| 7 am |
80 |
46.9 |
1.012 |
462 |
288 |
139 |
<Discussion>
腦下垂體會分泌抗利尿激素(anti-diuretic
hormone, ADH)以促進腎臟重吸收水份，若因腦下垂體本身分泌不足(中樞性尿崩，central diabetes
insipidus)，或腎臟對血管加壓素有抗性導致抗利尿激素無法發揮作用(腎性尿崩症，nephrogenic
diabetes insipidus)，都會造成尿崩症(diabetes insipidus,
DI)；病情嚴重時會造成脫水。臨床症狀有多尿，最初常被注意的症狀多為夜尿頻率太多而影響睡眠。另外因排尿過多、體液減少、脫水亦會造成口渴，尤其喜好冷水或冰水等。
每天的尿量大於2.5公升便稱為多尿（polyuria）。多尿的原因除了尿崩症，還有原發性多飲症（primary
polydipsia）、及滲透性利尿（osmotic
diuresis）。滲透性利尿患者常見於血糖高的糖尿病患者、最近接受放射線檢查施打顯影劑的患者等。另外服用利尿劑或含咖啡、酒等物質亦會造成多尿甚至有些藥物也會致使腎性尿崩症。一般對於多尿的患者，
除了病史的詢問外, 實驗室的檢查可以提供臨床判斷的參考。最重要是尿液的比重、滲透壓及血液的滲透壓。若尿液的比重小於1.005
或滲透壓小於200 mosm/kg時，即可排除滲透性多尿。進一步確定是否有尿崩症可以靠限水測試(water
deprivation
test)。接受限水試驗時，若尿液滲透壓可因應體液減少而正常反應，隨時間持續上升至超過血液的滲透壓，則可能是原發性多飲症或部分中樞性性尿崩症(central
partial
DI)。但限水後若尿液無法濃縮且尿液的比重仍然小於1.005，便是尿崩症(包括完全性中樞性尿崩症[central
complete DI]及腎性尿崩症)；我們的病人在限水後仍無法濃縮尿，故診斷為尿崩症而非原發性多飲症。尿崩症確診後,
再進一步鑑別中樞性及腎性尿崩症可藉限水-血管加壓素試驗(dehydration-vasopressin
tests)。在注射desmopressin後，若尿液的滲透壓增加超過50%，便可以診斷為中樞性尿崩症而非腎性尿崩症。造成中樞性尿崩症的原因不少，包括自體免疫或血管性疾病、腫瘤、發炎浸潤、頭部手術或傷害等等。找不到原因的則歸為不明原因。至於影像學檢查，核磁共振（T1-weighted）會發現腦下腺後葉缺乏高訊號，但不具專一性。另外，不明原因之中樞性尿崩症常會伴隨有腦下腺前葉荷爾蒙缺乏，故需同時檢查腦下腺前葉功能。治療通常是給予血管加壓素(desmopressin)。
<參考文獻>
- Ball SG, Barber T, Baylis PH: Tests of
posterior pituitary function. J Endocrinol Invest 2003;26(7
Suppl):15-24.
- Maghnie M: Diabetes insipidus. Horm
Res 2003;59(Suppl 1):42-54.
- Ghirardello S, Garre ML, Rossi A: The
diagnosis of children with central diabetes insipidus. J
Pediatr Endocrinol Metab 2007;20:359-75.
- Maghnie M, Cosi G, Genovese E,et al:
Central diabetes insipidus in children and young adults. N
Engl J Med 2000;343(14):998-1007.
|
Case Discussion
繼續教育考題