< Chief
complaint >
Polyuria for three years
< Case
presentation >
This 21-year-old previously health girl presented
with polyuria for three years, which made her to urinate
every hour. The urine was clear and light-colored. She also
felt thirsty frequently, and had water intake of up to 10
liters per day. Nocturia and ensuing disturbed sleeping
developed, which resulted in easy-anxiety and daytime
somnolence. She denied history of head trauma, surgery, eating
disorder or medication use before. She had no family history
of polyuria, either.
< Physical
examination >
Physical examination revealed a 55 kg, 155 cm-tall woman with
blood pressure 120/70 mmHg. She appeared anxious and thirsty.
Her respirations and temperature were normal and her pulse
rate was 80 beats per minute. The pupils were isocoric (3/3
mm) with prompt light reflex. Neither facial deformity nor
oropharyngeal lesion was found. The neck was supple without
goiter or lymphadenopathy. Chest, abdominal and extremity
examinations were normal. Neurological examinations including
visual field, motion of eye balls and hearing function were
normal.
< Course and treatment
> Biochemical
studies and complete blood count were within the normal range.
Daily water intake and urine volume were approximately 13
liters, respectively. Urinalysis revealed a specific gravity
of 1.002. Urine and plasma osmolality were 73 and 282 mosm/kg,
respectively. Baseline serum hormone levels were as follows:
high sensitivity thyroid-stimulating hormone (hsTSH) 2.5
μIU/mL (normal, 0.1-4.5), free thyroxine (FT4) 0.95 ng/dL (normal, 0.6-1.75),
corticotropin (ACTH) 20 pg/mL (normal, 10-65), cortisol 19
μg/dL (normal, AM 5-25), prolactin 7.8 ng/mL (normal,
1.4-24.2), growth hormone (hGH) 0.09 ng/mL (normal, 0.06-5.0),
follicle-stimulating hormone (FSH) 9.69 IU/L (normal, 3.4-10),
luteinizing hormone (LH) 7.67 IU/L (normal, 1.6-8.3) and
estradiol 120 pg/mL (normal in follicular phase, 73.4-367).
Both microsomal antibodies (MA) and thyroglobulin antibodies
(TA) were negative. Electrocardiogram was normal.
Roentgenologic examinations, including chest films and skull
films with stereoscopic views of the sella turcica were
unremarkable. Magnetic resonance imaging (MRI) demonstrated
normal-sized pituitary gland with mildly prominent pituitary
stalk and absence of the high signal of the posterior
pituitary lobe(Fig 1
& Fig
2
).
Dehydration test containing hourly measurements of urine
volume, urine specific gravity, urine and plasma osmolality
was carried out. The test was terminated after four hours when
the weight decreased by 3%. She then received an intramuscular
injection of 2 μg desmopressin acetate. The
dehydration-desmopressin tests revealed no increase in urine
concentration during dehydration but prompt response to
vasopressin (table 1). The patient was treated with oral
desmopressin twice daily. Her daily urine volume decreased to
two liters. She regularly followed up at our hospital.
<
Laboratory data >
Table 1. Dehydration-vasopressin tests
(Dehydration since 8am; stop water
deprivation with desmopressin acetate (DDAVP) 2 μg IM
given at noon)
Time
|
BW (kg) |
UA (ml/h) |
Sp. Gr
|
Uosm (mosm/kg) |
Posm (mosm/kg) |
P[Na+] (meq/L) |
BP (mmHg) |
8am |
55 |
300 |
1.002 |
73 |
282 |
144 |
136/80 |
9am |
55 |
600 |
1.002 |
72 |
282 |
|
124/78 |
10am |
54 |
510 |
1.002 |
80 |
287 |
144 |
144/92 |
11am |
53.5 |
540 |
1.002 |
90 |
292 |
|
142/86 |
0pm |
53 |
400 |
1.003 |
128 |
295 |
147 |
140/80 |
1pm |
54 |
100 |
1.012 |
440 |
284 |
|
144/96 |
2pm |
55 |
60 |
1.013 |
470 |
282 |
141 |
143/86 |
3pm |
55 |
90 |
1.012 |
430 |
279 |
|
138/84 |
4pm |
55 |
35 |
1.012 |
398 |
279 |
138 |
136/86 |
BW =
body weight; UA= urine amount; Sp. Gr. = specific gravity of
urine; Uosm:= urine osmolality; Posm = plasma osmolality;
P[Na+] = plasma
sodium concentration; BP = systolic blood pressure / diastolic
blood pressure
< Discussion
>
每天尿量大於3公升稱為多尿(polyuria)。多尿的原因很多,包括尿崩症(diabetes
insipidus),原發性多飲症(primary polydipsia)和滲透性利尿(osmotic
diuresis)。滲透性利尿患者之尿液滲透壓接近血漿滲透壓;而尿崩症和原發性多飲症患者的尿液滲透壓就會遠低於血漿滲透壓。尿液的比重小於1.005
(滲透壓小於200
mosm/kg)時,通常可以排除滲透性多尿。尿崩症患者血中鈉離子濃度和滲透壓經常是正常或增加的,而原發性多飲症病人的血漿和尿液則是較稀釋的。接受限水試驗(dehydration
test)時,完全性尿崩症(complete
DI)的病人仍會有大量的尿液,而且尿液的比重仍然小於1.005;但是,在原發性多飲症的病人身上可以看到尿液滲透壓隨著時間持續上升至超過血液的滲透壓。因此我們的病人診斷為尿崩症而非原發性多飲症。
尿崩症分為中樞性尿崩症(central
)及腎性尿崩症(nephrogenic),前者是因為缺乏血管加壓素(vasopressin),而後者是腎臟對血管加壓素有抗性。藉由限水及血管加壓素試驗(dehydration-vasopressin
tests)可以確定診斷。我們的病患注射desmopressin後,尿液的滲透壓增加超過50%,因此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,包括浸潤(包括結節病和組織細胞增生症
X,sarcoidosis and histiocytosis X)、發炎(lymphocytic
hypophysitis)、自體免疫或血管性疾病、中樞神經系統腫瘤(如生殖細胞瘤,germinoma)、頭部手術或意外造成的傷害,及其他非常少見的病因,如因為遺傳基因缺損造成血管加壓素合成異常。然而,約30%到50%是不明原因(idiopathic)的。
核磁共振影像檢查(T1-weighted)會發現腦下腺後葉缺乏高訊號,這是中樞性尿崩症一個非專一性的特點。雖然不具專一性,但是如果同時出現漏斗或腦下腺柄變厚,則表示有局部發炎、浸潤或自體免疫疾病或生殖細胞瘤。生殖細胞瘤通常會使得腦下腺前葉變大且柄變厚;然而,如果是發炎反應或自體免疫疾病反而會使得腦下腺前葉變小而柄變厚。但是浸潤或慢性發炎疾病常常會同時影響身體其他器官而伴隨著其他系統的症狀。雖然不能完全排除自體免疫疾病造成我們的病人出現尿崩症,但是目前的診斷仍為不明原因中樞性尿崩症。
有些不明原因之中樞性尿崩症也會伴隨有腦下腺前葉荷爾蒙缺乏,所以這些病患應該同時檢查腦下腺前葉功能。治療通常是給予血管加壓素(desmopressin),有口服或鼻噴劑可以選擇。治療時應隨時注意體重、血壓及電解質是否平衡。
< References
>
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