Carcinoid syndrome revealed by chronic diarrhea and isolated severe tricuspid regurgitation

Carcinoid syndrome is an uncommon manifestation of metastatic neuroendocrine tumor (NET) and may present without classic flushing or bronchospasm. We describe a woman in her 50s with hypertension treated with hydrochlorothiazide who presented with confusion, severe hyponatremia with a serum sodium concentration of 114 mmol/L (reference range, 135-145 mmol/L), chronic watery diarrhea, bilateral leg edema, and 40-lb weight loss. Computed tomography (CT) revealed a calcified mesenteric mass and multiple hepatic lesions. Serum chromogranin A was 1434 ng/mL (SI: 1434 µg/L) (reference range, <100 ng/mL [SI: <100 µg/L]), and 24-hour urinary 5-hydroxyindoleacetic acid (5-HIAA) was 108 mg/24 hours (SI: 565 µmol/24 hours) (reference range, <6 mg/24 hours [SI: <31 µmol/24 hours])-well above the threshold associated with carcinoid heart disease (CHD). Transthoracic echocardiography demonstrated severe tricuspid regurgitation with retracted leaflets, consistent with CHD. Liver biopsy confirmed a well-differentiated grade 2 NET. Urine sodium <20 mmol/L and urine osmolality 188 mOsm/kg indicated volume depletion from gastrointestinal losses, aggravated by hydrochlorothiazide. Hydrochlorothiazide was discontinued; isotonic saline, octreotide, and furosemide improved hyponatremia, diarrhea, and edema. Chronic diarrhea with isolated right-sided valvulopathy should prompt evaluation for carcinoid syndrome even when electrolyte derangement dominates.