THU514 Atypical Presentation Of Birt-Hogg-Dubé Syndrome With Poorly Differentiated Follicular Thyroid Cancer And Paraganglioma

Disclosure: K. Lertdetkajorn: None. J. Haw: None. J.E. Paysour: None. Background: Birt-Hogg-Dubé syndrome (BHDS) is a rare genetic disorder typically presenting with skin hamartomas, renal tumors, and lung cysts. BHD is caused by germline mutations of the folliculin (FLCN) gene. We present the case of a patient with follicular thyroid cancer and paraganglioma diagnosed with BHDS. Case: A 64-year-old female was noted to have progressive enlargement of a neck mass over six months following admission for a hypertensive emergency. CT neck demonstrated a heterogeneous mass centered within the left thyroid lobe measuring 10.4 x 8.6 x 7.6 cm with internal calcifications. TSH was normal. FNA of this mass was suspicious for follicular neoplasm, and she underwent a total thyroidectomy. The pathology reported poorly differentiated adenocarcinoma of the thyroid gland, follicular variant, pT3aN0M0 with positive margins, and lymph-vascular space invasion (LVI). FDG-PET/CT scan showed postsurgical changes of a total thyroidectomy with ill-defined FDG uptake along the left thyroid bed, 3 x 2.8 cm portacaval lymph node (SUV of 9.6) and focal soft tissue FDG avid rectal abnormality. MRI abdomen demonstrated a 4.0 x 4.1 x 3.2 cm soft tissue mass characterized by arterial hyperenhancement and washout in the portacaval region broadly interfacing with the IVC, main portal vein, and left renal vein. EGD was unremarkable, but an EUS demonstrated 3.7 x 3.5 hypoechoic, well-circumscribed, mild-vascular hypoechoic portocaval mass. FNA of this mass was consistent with paraganglioma. Laboratory results supported the diagnosis of paraganglioma with urine metanephrine 9661 mcg/24 h (224 - 832 mcg/24 h) and urine normetanephrine 9457 mcg/24 h (122 - 676 mcg/24 h). The patient was referred for genetic testing to investigate whether the co-existence of follicular thyroid cancer and paraganglioma was secondary to a genetic disorder. The germline genetic testing revealed the pathogenic variant, c.1436dup (p.Thr481Hisfs*5), identified in the FLCN gene with no detections of VHL or SDH complex variants, confirming the diagnosis of BHDS. The patient later underwent a colonoscopy and was found to have stage I colon cancer. Some early reports have shown an association between BHDS and colon tumors. The patient decided not to have any surgery at this time. She continues to follow up in the clinic and takes levothyroxine for suppressive goals. Octreotide LAR, along with blood pressure medications including phenoxybenzamine, was started to treat her paraganglioma. Conclusion: Patients with BHDS may present with atypical clinical manifestations. Genetic testing will aid in diagnosing a germline mutation in the FLCN gene. The association between thyroid cancer and BHDS has been reported previously; however, paraganglioma as a spectrum of BHDS has not been published. Further reported cases and research may provide additional data to investigate the relationship between BHDS and paraganglioma. Presentation: Thursday, June 15, 2023