Syndrome of inappropriate antidiuretic hormone release as the initial presentation of adenocarcinoma of the colon

Syndrome of inappropriate antidiuretic hormone release (SIADH) is a condition defined by the unsuppressed release of antidiuretic hormone (ADH) from the pituitary gland or nonpituitary sources or its continued action on vasopressin receptors. Of the many causes of SIADH, an important one includes tumours that secrete ADH. We describe a rare case of a patient with colonic adenocarcinoma presenting initially as SIADH. A 60-year-old man presented with confusion and vomiting. Over the previous month he had fatigue and loss of weight. Baseline investigations showed a low serum sodium level of 108mmol/l. He was euvolaemic on examination and fulfilled the criteria for SIADH. Further evaluation and imaging tests revealed that the patient had adenocarcinoma of the colon. It is remarkable that our patient did not present with any of the cardinal symptoms/signs suggestive of colorectal carcinoma including haematochezia, change in bowel habits or iron-deficiency anaemia. Initial therapy with hypertonic saline, fluid restriction and salt diet for management of SIADH was unsuccessful. Tolvaptan was added to the treatment regimen and the patient improved dramatically. Oncology consultation was initiated, and chemotherapy for the carcinoma was planned.