Syndrome of inappropriate antidiuretic hormone secretion and Leser–Trélat syndrome as uncommon paraneoplastic manifestations of renal malignancy – a geriatric experience: a case report

BACKGROUND: Leser–Trélat syndrome, which manifests as eruptive multiple seborrheic keratoses, is a rare paraneoplastic sign. Hyponatremia in the elderly population is an often overlooked but potentially sinister biochemical abnormality. Cancer-related causes of hyponatremia include syndrome of inappropriate antidiuretic hormone secretion, cerebral or renal salt wasting, and adrenal dysfunction. We report a case of an elderly man who presented with both syndrome of inappropriate antidiuretic hormone secretion and Leser–Trélat syndrome, and was eventually found to have renal malignancy. CASE PRESENTATION: A 74-year-old indigenous Malaysian man with underlying chronic kidney disease presented with recurrent admissions for hyponatremia with parameters indicative of syndrome of inappropriate antidiuretic hormone secretion, constitutional symptoms, and diffuse skin lesions suggestive of multiple seborrheic keratoses. A radiological workup revealed metastatic renal cell carcinoma with evidence of metastasis to the brain, adrenal glands, bone, and lungs. CONCLUSIONS: To the best of our knowledge, renal malignancy presenting as syndrome of inappropriate antidiuretic hormone secretion and Leser–Trélat concurrently is rare. The causes of hyponatremia in the elderly, approach to investigation, and value as a poor prognostic marker in malignancy are highlighted. We also discuss Leser–Trélat syndrome, its pathophysiology, and its possible implications on clinical practice.