Endocrine Abstracts

81-year-old male was admitted with malaise and hyponatremia of 118 mmol/l within 24 hours of undergoing transurethral resection of the prostate (TURP), performed to alleviate lower urinary tract obstructive symptoms associated with normal PSA prostate cancer. Initially, TURP syndrome secondary to absorption of hypotonic irrigation fluid causing acute water intoxication was thought to be responsible. However, clinical evaluation demonstrated a SIAD picture; euvolemic state, serum osmolality of 255 mOsm/kg, urine osmolality of 915 mOsm/kg, and urine sodium of 87 mmol/l. The patient was discharged with instructions for fluid restriction and outpatient monitoring but worsening hyponatremia led to readmission. CT CAP was largely unremarkable except for a calcified, enlarged prostate and enlarged iliac lymph node and brain imaging was normal. Despite attempts with fluid restriction and demeclocycline, sodium levels showed minimal improvement. A further review of prior urological investigations revealed malignancy and prostate biopsy findings consistent with high-grade neuroendocrine carcinoma (95%). Serum chromogranin A was markedly elevated (384 pmol/l), supporting the diagnosis of active NET (Neuro endocrine tumour). A bone scan showed metastatic skeletal lesions. Given the aggressive nature of the tumour, palliative chemotherapy with carboplatin and etoposide was initiated, along with androgen deprivation therapy (ADT). Unfortunately, the patient’s condition deteriorated, and a repeat CT scan revealed widespread organ metastases. Following a multidisciplinary discussion and palliative team review, the patient was sadly transitioned to End of life care This case highlights a rare association between SIAD and NEPC. SIAD is an extremely rare paraneoplastic manifestation in prostate cancer, with the reported cases involving aggressive adenocarcinoma or neuroendocrine pathology. Clinicians should consider this explanation beyond the classic association with small cell lung cancer, in cases of unexplained and persistent hyponatremia and SIAD.