AN INTERESTING CASE OF POLYURIA

Polyuria has generally been defined as a state of urinary output exceeding 3 litres per day in adults. In the absence of glucose induced osmotic diuresis in uncontrolled diabetes mellitus, the three major causes of polyuria are as follows 1. Central Diabetes Insipidus 2. Nephrogenic Diabetes Insipidus 3. Primary Polydipsia which is primarily seen in adults and adolescents. A 42 year old female presented with complaints of increase in urinary frequency and increase in thirst sensation of 3 months duration. She had polyuria with urine output of 14 L per day. She was not on any medication. Her routine investigations including USG abdomen done to rule out structural kidney disease were within normal limits. She had normal plasma osmolarity and serum sodium levels with low urine specific gravity and low urine osmolarity indicating water diuresis .We proceeded with Water Deprivation Test to differentiate between Diabetes Insipidus and Primary Polydipsia, which showed that even after 2 hours of water deprivation and serum osmolarity rise to 301 mosmkg, the urine osmolarity was still low (60 mosm) which confirmed the diagnosis of Complete Diabetes Insipidus (DI). To differentiate between Central and Nephrogenic DI, 20 micrograms of Vasopressin was administered intranasally and after one hour, the urine osmolarity became more than 50 percent the pre test value, which indicated that the patient had complete central DI. MRI Brain showed normal anterior pituitary, pituitary stalk, no mass lesion with absence of bright spot in posterior pituitary region which normally indicates the presence of stored AVP granules. ANA and Mantoux were negative. Other anterior pituitary hormonal assays were within normal limits. Hence our final diagnosis was Complete Central Diabetes Insipidus of Idiopathic cause.