MON-033 Neuroendocrine Carcinoma Presenting As Misdiagnosed Chronic Orthostatic Hypotension

Abstract Disclosure: N. Patel: None. A. Reddy: None. K. Ali: None. A.N. Mukhtar: None. P. Reddy: None. Gallbladder Neuroendocrine tumors (NETs) account for 0.5% of all diagnosed NETs. NETs that metastasize to the liver can lead to carcinoid syndrome as the liver is unable to inactivate the released vasoactive substances. Classically, carcinoid syndrome presents as diarrhea, bronchospasm, flushing, or right sided heart disease. Less than 1% of patients with NETs will develop carcinoid syndrome. We highlight a case of gallbladder neuroendocrine carcinoma leading to carcinoid syndrome and presenting as chronic refractory orthostatic hypotension that responded to Octreotide. A 37-year-old female with a past medical history including type 1 diabetes mellitus, chronic refractory orthostatic hypotension on midodrine and fludrocortisone, and a chronic grade 4 decubitus sacral ulcer presented to the hospital with weakness and abdominal pain. Admission vitals included a heart rate of 72 beats per minute and blood pressure of 85/55mmHg with positive orthostatic vitals despite being compliant with home medications. Magnetic resonance cholangiopancreatography showed a 7 centimeter complex lesion within the gallbladder fossa with tissue infiltration along the margin of the liver, microlesions in bilateral hepatic lobes, and lymphadenopathy. Liver biopsy showed carcinoma with neuroendocrine features given positive chromogranin A, synaptophysin, and Ki-67 of 80%. Vasoactive intestinal polypeptide and gastrin levels were within normal limits, with elevated 24-hour 5-Hydroxyindoleacetic acid at 20 milligrams over 24 hours. She was started on Octreotide 50 micrograms three times a day with significant improvement in orthostatic hypotension. She was ultimately diagnosed with a gallbladder neuroendocrine carcinoma with metastasis to the liver, leading to carcinoid syndrome. She was deemed a poor candidate for chemotherapy given advanced disease and large gluteal ulcers, and proceeded with palliative measures. High amounts of circulatory serotonin cause orthostatic hypotension by binding to widespread 5- hydroxytryptamine (5-HT) receptors, leading to vascular vasodilation of the skeletal muscles. When bound to 5-HT3 receptors on the vagus nerve, an inhibitory reflex within the inferoposterior wall of the left ventricle, known as the Bezold-Jarisch reflex, activates the parasympathetic nervous system presenting as bradycardia and hypotension. This is primarily during periods of decreased preload to the heart, such as standing. Octreotide, a somatostatin analog, binds to somatostatin receptors (SSTRs); particularly SSTR 2 and SSTR 5, which are expressed by the cells in NETs. Once bound, it inhibits the release of serotonin by blocking voltage-dependent calcium channels, activating inhibitory G proteins, and directly preventing the release of serotonin; all of which help improve orthostatic hypotension and carcinoid syndrome symptoms. Presentation: Monday, July 14, 2025