Changes in Urinary Aquaporin 2 and Serum Sodium After Catheterization in Elderly Patients with Syndrome of Inappropriate Antidiuretic Hormone and Urinary Retention: A Preliminary Hospital-based Study in Yangon, Myanmar.

BACKGROUND

The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the most common electrolyte disorder among elderly patients. Chronic urinary retention has also been implicated in the development of SIADH. The mechanism by which urinary retention leads to SIADH remains unclear. Increased responsiveness of the collecting ducts to arginine vasopressin has been observed in elderly patients with urinary retention. This study aims to evaluate whether SIADH in elderly patients with urinary retention is associated with increased urinary aquaporin 2 (U-AQP2) levels and whether the insertion of an indwelling catheter with fluid restriction, without the administration of 3% saline, can lower the U-AQP2 level, leading to the resolution of SIADH.

METHOD

This hospital-based clinical intervention study was conducted from January 2022 to January 2023. Eighteen elderly patients who met the selection criteria for euvolaemic SIADH (identified by Bartter and Schwartz criteria) associated with urinary retention, after excluding other causes, were selected. Serum sodium (Nas), serum osmolality (Osms), U-AQP2 levels, urinary osmolality (Osmu) and 24-hour urine volume on days 1 and 4 post-catheterization were assessed and compared. Clinical responses, including neurological signs and symptoms (Glasgow Coma Scale [GCS]), were also recorded.

RESULTS

All 18 cases had comorbidities and were in a range of severe hyponatraemia, defined as Nas<125 mmol/L. Nas levels significantly increased (p<0.05) on days 2 and 4 after the drainage of residual urine, with mean (± standard deviation) changes of 8.39 (± 5.7) and 15.67 (± 5.6) mmol/L, respectively, from a baseline of 110.7 mmol/L. Osms significantly increased (p<0.05) from 240.01 (± 15.68) mOsm/kg on day 1 to 272.74 (± 13.41) mOsm/kg on day 4 post-catheterization. The mean urinary aquaporin:creatinine ratio significantly decreased (p<0.05) from 3,348.01 (± 2,127.82) fmol/mg Cr on day 1 to 1,135.27 (± 1,194.42) fmol/mg Cr on day 4. The mean Osmu significantly decreased (p=0.00) from 450.67 (± 187.3) mOsm/kg on day 1 to 229.33 (± 123.56) mOsm/kg on day 4. The mean urine volume significantly increased (p<0.05) from 1,610.00 (± 530.15) mL on day 1 to 2,725.56 (± 898.29) mL on day 4. All patients showed neurological improvement, with the mean GCS increasing from 11 to 14, without complications of osmotic demyelination syndrome.

CONCLUSION

U-AQP2 levels are elevated in elderly patients with SIADH with urinary retention. After catheterization, these levels decrease, leading to the spontaneous resolution of hyponatraemia without complications.