CONFIRMING DIAGNOSIS Diagnosis requires evidence of vasopressin deficiency, resulting in the kidneys’ inability to concentrate urine during a water deprivation test.
In this test, after baseline vital signs, weight, and urine and plasma osmolalities are obtained, the patient is deprived of fluids and observed to make sure he doesn’t drink anything surreptitiously. Hourly measurements then record the total volume of urine output, body weight, urine osmolality or specific gravity, and plasma osmolality. Throughout the test, blood pressure and pulse rate must be monitored for signs of orthostatic hypotension. Fluid deprivation continues until the patient loses 3% of his body weight (indicating severe dehydration). When urine osmolality stops increasing in three consecutive hourly specimens, patients receive 5 units of aqueous vasopressin subcutaneously (S.C.).
Hourly measurements of urine volume and specific gravity continue after S.C. injection of aqueous vasopressin. Patients with pituitary diabetes insipidus respond to exogenous vasopressin with decreased urine output and increased specific gravity. Patients with nephrogenic diabetes insipidus show no response to vasopressin.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Pituitary tumors:
Diagnosis
(Professional Guide to Diseases (Eighth Edition))
❑Skull X-rays with tomography show enlargement of the sella turcica or erosion of its floor; if GH secretion predominates, X-rays show enlarged paranasal sinuses and mandible, thickened cranial bones, and separated teeth.
❑ Carotid angiogram shows displacement of the anterior cerebral and internal carotid arteries if the tumor mass is enlarging; it also rules out intracerebral aneurysm.
❑ Computed tomography scan may confirm the existence of the adenoma and accurately depict its size.
❑ Cerebrospinal fluid (CSF) analysis may show increased protein levels.
❑ Endocrine function tests may contribute helpful information, but results are commonly ambiguous and inconclusive.
❑ Magnetic resonance imaging differentiates healthy, benign, and malignant tissues as well as arteries and veins.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Diabetes insipidus:
Diagnosis
(Handbook of Diseases)
Urinalysis reveals almost colorless urine of low osmolality (50 to 200 mOsm/kg, less than that of plasma) and low specific gravity (less than 1.005). However, a diagnosis requires the water deprivation test to provide evidence of vasopressin deficiency, resulting in the kidneys’inability to concentrate urine.
Water deprivation test
In this test, after baseline vital signs, weight, and urine and plasma osmolalities are obtained, the patient is deprived of fluids and observed to make sure he doesn’t drink anything surreptitiously. Hourly measurements then record the total volume of urine output, body weight, urine osmolality or specific gravity, and plasma osmolality. Throughout the test, blood pressure and pulse rate must be monitored for signs of orthostatic hypotension.
Fluid deprivation continues until the patient loses 3% of his body weight (indicating severe dehydration). When urine osmolality stops increasing in three consecutive hourly specimens, the patient receives 5 units of aqueous vasopressin subcutaneously (S.C.).
Hourly measurements of urine volume and specific gravity continue after S.C. injection of aqueous vasopressin. Patients with pituitary diabetes insipidus respond to exogenous vasopressin with decreased urine output and increased specific gravity. Patients with nephrogenic diabetes insipidus show no response to vasopressin.
» READ BOOK EXCERPT ONLINE »
Source: Handbook of Diseases, 2003
Pituitary tumors:
Diagnosis
(Handbook of Diseases)
❑ Magnetic resonance imaging (MRI), cranial computed tomography (CT) scanning, or skull X-rays with tomography show enlargement of the sella turcica or erosion of its floor; if growth hormone secretion predominates, X-ray films show enlarged paranasal sinuses and mandible, thickened cranial bones, and separated teeth. MRI and CT scan show the location and size of the adenoma.
❑ Carotid angiography shows displacement of the anterior cerebral and internal carotid arteries if the tumor mass is enlarging; it also rules out intracerebral aneurysm.
❑ Cerebrospinal fluid analysis may show increased protein levels.
❑ Endocrine function tests may contribute helpful information, but results are often ambiguous and inconclusive.
» READ BOOK EXCERPT ONLINE »
Source: Handbook of Diseases, 2003
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