FRI364 A Case Of Carcinoid Syndrome Symptoms Masked By Niacin Use

Disclosure: S. Yang: None. R. Sharag Eldin: None. D. Teves Qualler: None. Case Presentation: A 72 male presented with worsening of facial flushing and diarrhea for 10 years. The patient described episodic feeling of hotness in the face associated with red- purplish discoloration of his facial skin lasting for 2 to 3 minutes. He has had 5 to 6 episodes per day. The patient reported the use of Niacin in the past and it was believed that it was the cause of his flushing episodes despite its persistence for years after stopping it. The patient also suffered from long standing diarrhea which started around the same time of the flushing. Diarrhea has been watery or loose and he has 5 to 6 bowel movements a day. His symptoms were concerning for Carcinoid syndrome and a 24-hour urine collection for HIAA showed elevated HIAA to 108.7 mg/24 hour (<6 mg/24 hour). A CT scan of the abdomen revealed a 1.8 cm wall thickness in the cecum and a 3.6 cm spiculated mesenteric mass with central calcification with multiple hypervascular masses in the liver concerning for a metastatic neuroendocrine tumor. Core biopsy of one of the liver masses showed a well differentiated neuroendocrine tumor. He was also found to have tricuspid valve regurgitation as well as a Glycohemoglobin of 9%. The patient was treated medically with octreotide rather than surgery due to the significant disease burden. Interestingly, he was initially started on Lanreotide but developed foreign body granulomas at the injection sites. Discussion: Carcinoid-syndrome is a category of well-differentiated neuroendocrine neoplasms. The overproduction of serotonin is most used to assess the presence of carcinoid syndrome via its breakdown product 5- HIAA in the urine. Symptoms from niacin supplementation are variable and may include flushing and constipation. Patient’s flushing presented for years after discontinuing niacin supplementation. However, clinicians continued to attribute it to its use despite typical resolution of symptoms within 3 hours of discontinuing use. Niacin exposure may have been a mimicker of his underlying neuro endocrine neoplasia (NEN) as diarrhea is also an overlapping feature as seen in our patient’s presentation. DM as seen in our patient is not well documented in relation to carcinoid syndrome. One study (n=10) of the patients with functionally active NENs, 70% had borderline to diabetic-level blood glucose. Of the patients with carcinoid syndrome, there was no significant difference in fasting plasma glucose concentration or fasting plasma insulin concentration when compared to age-matched normal volunteers. Conclusion: Clinicians should have low level of suspicion in diagnosing carcinoid syndrome in the presence of typical symptoms of flushing and diarrhea. Due to the past use of niacin, our patient’s diagnosis was delayed despite the persistence of flushing years after stopping it. Presentation: Friday, June 16, 2023