7553 Thyroid Paraganglioma: A Complex Tale of the Familiar Thyroid Nodule

Abstract Disclosure: V. Moorthy: None. A. Kondapally: None. L.E. Kimball-Ravari: None. Background: Thyroid paragangliomas are rare and often misdiagnosed on fine-needle aspiration (FNA). Clinical Case & Discussion: A 58-year-old female presented with an asymptomatic “cold” thyroid nodule. Ultrasound demonstrated a 2 cm hypoechoic nodule in the isthmus. FNA yielded a follicular lesion of undetermined significance, and genomic sequencing estimated a 50% risk of malignancy prompting the patient to opt for total thyroidectomy. Histopathology and immunohistochemistry (IHC) confirmed the diagnosis of benign paraganglioma (PGL). SDH-B (succinate dehydrogenase subunit B) was notably absent on IHC. Past medical history is significant for hysterectomy for uterine fibroids and obesity, along with a confirmed family history of Hereditary Leiomyomatosis with Renal Cell Cancer (HLRCC). The patient and several family members tested positive for a pathogenic variant of fumarate hydratase (FH) gene implicated in HLRCC and undergo annual MRIs for cancer surveillance. The loss of SDH-B suggests underlying mutation. Germline SDH mutations occur in 20% of patients with pheochromocytoma and PGLs, predisposing to hereditary syndromes. PGLs are catecholamine-secreting neuroendocrine tumors with carotid body and jugular PGLs accounting for 80% of head and neck PGLs (HNPGLs). Thyroid PGLs originate from the inferior laryngeal paraganglia. They are very rare, often non-secretory, and commonly present as asymptomatic solitary nodules. For these reasons, FNA, while contraindicated, is frequently performed. If FNA is considered, pre-procedural alpha-adrenergic blockade is recommended, although catecholamine secretion triggered by FNA is uncommon. Thyroid PGLs are misdiagnosed on FNA as other thyroid neoplasms. Awareness of the more unique cytopathology of thyroid PGLs and a comprehensive IHC can aid in accurate diagnosis. Interestingly, SDH (complex 2) and FH are closely linked enzymes in the Krebs cycle. Emerging evidence correlates germline FH mutations and hereditary pheochromocytoma-paraganglioma. PGLs are less commonly associated with MEN 2A and 2B, NF type 1, VHL, and Carney-Stratakis syndrome and Carney triad. Therefore, additional testing for SDH, RET, VHL and MAX genes was recommended in this case. Total thyroidectomy or lobectomy with or without elective lymph node dissection remains the treatment of choice. Annual 24-hour urine and plasma metanephrine testing will help screen for potential recurrence. Use of GLP1 agonists for weight loss in this patient warrants further genetic and safety evaluation. Clinical Lesson/Conclusion: Often misdiagnosed on FNA, thyroid paragangliomas are rare, with multiple genetic predispositions. FNA is contraindicated and if considered, must be performed after alpha-blockade. Germline SDH mutations are implicated in PGLs and increasing evidence links FH mutations to hereditary PGLs. Presentation: 6/3/2024