A RARE CASE OF NEPHROGENIC DIABETES INSIPIDUS IN AN ADULT MALE: A DIAGNOSTIC PROBLEM

Diabetes insipidus (DI) is a rare disorder of fluid balance found in 1 in 25,000 people or about 0.004% of the global population. It is characterized by the excretion of large amounts of hypotonic urine, with urinary characteristics like insipid, hypotonic, and diluted. Diabetes insipidus can be caused by deficiency of the arginine vasopressin hormone (AVP), also known as antidiuretic hormone (central diabetes insipidus) and resistance to AVP at the receptors in the kidneys (nephrogenic diabetes insipidus).

Nephrogenic DI is caused by a decreased sensitivity of the kidneys to the antidiuretic effects of physiological AVP. Nephrogenic DI can occur congenitally or acquired. The incidence of Nephrogenic DI in adults is still not precisely known. Since DI cases in adults are still not widely found, it is very important to conduct an adequate diagnosis when encountering a patient with polyuria. In this case report, we discuss the diagnostic and therapeutic approach for a patient with suspected Nephrogenic DI.

A 61-year-old gentleman was admitted due to worsening nausea and vomiting in the week preceding admission. The patient also complained of abdominal pain and constipation, but flatus could still occur spontaneously. The patient sometimes appeared confused, restless, and did not respond appropriately to questions during communication over the past 2 months. The patient also reported an increase in urination frequency for 9 months, but the patient stated there was no pain during urination, blood in the urine, or foamy urine.

The physical examination was unremarkable. At presentation, serum creatinine was 1.1 (no baseline was recorded previously) with serum sodium 114 mmol/L, serum osmolarity 236, potassium 2.5 mmol/L, and chloride 68 mmol/L. Evaluation of the patient's urine production is around 9000 ml over 24 hours. The serology results for hepatitis B, hepatitis C, and HIV were negative. Procalcitonin examination showed low results with a value of 0.05. HbA1c was also at 5.9%. A chest X-ray was performed, which showed a prominent heart accompanied by elongation of the aorta and no abnormalities in the lungs. The abdominal X-ray was normal. A previous colonoscopy revealed the presence of external hemorrhoids and a single flat polyp in the descending colon. The result of the abdominal ultrasound examination was normal. The result of the head CT scan was normal.

After electrolyte correction was performed on the patient, the patient's potassium (3.8 mmol/L) and sodium (135 mmol/L) level became normal with normal plasma osmolarity (290 mOsm/kg). However, it was observed that his urine output was gradually reduced to 7000 ml for 24 hours. After the potassium results were normal, a 24-hour urinary examination and urine osmolarity test were conducted.

Table 1 24-Hour Urinary Examination and Urine Osmolarity Test

These findings suggest there was nephrogenic diabetes insipidus in the patient. The water deprivation test could not be performed on the patient because the patient was uncooperative. Copeptin test was not available.

A therapeutic challenge was performed with the administration of Hydrochlorothiazide (HCT) therapy at a dose of 3 x 25 mg. After correction of hypokalemia and administering HCT to the patient, the patient's vital signs were found to be stable with urine output decreased to 1200 ml. For three days, an adjustment of the HCT dose was made. For the second day, the initial HCT dose of 3 x 25 was reduced to 2 x 25 mg. With the use of HCT at 2 x 25 mg and a maintenance infusion of 500 ml/ 24 hours normal saline, along with 2200 ml daily fluid intake, the urine output was 3500 ml. In the third day, the HCT dose was reduced to 3 x 12.5 with an infusion of 500 ml and a fluid intake restriction of 1500 ml. The patient's urine output was 2100 ml. He was discharged without complain and with normal amount of urine production.

Nephrogenic DI cases are not commonly found in adults, but the treatments are rather straightforward and yield favorable results. This case highlights the importance of accurate clinical judgement in diagnosing patient with polyuria. Although there were limitations due to inability to perform water deprivation tests and copeptin tests, there are still other methods to exclude the possibility of central DI by administering a challenge therapy for Nephrogenic DI. The successful challenge therapy, which involved hydrochlorothiazide, also emphasized that nephrogenic DI therapy is quite straightforward when the clinical suspicion is accurate. Awareness and appropriate clinical judgment can narrow down the differential diagnosis in patients, facilitating a prompt and precise initiation of medication, resulting in a better outcome for the patient.