488 Sporadic Parathyroid Carcinoma with Diverse Histomorphology and Atypical Neurologic Presentation: A Rare Case Report

Introduction/Objective Parathyroid carcinoma (PC) is the rarest endocrine malignancy, with no standardized staging system. It accounts for a small fraction of primary hyperparathyroidism cases and is often difficult to distinguish from atypical parathyroid neoplasms. We report a unique case of PC with an unusual initial presentation and multiple histologic patterns. Methods/Case Report A 67-year-old African-American woman presented with seizure-like activity, tonic contractions, and right gaze preference. Imaging revealed a necrotic lesion near the left thyroid lobe and prominent level IV lymphadenopathy. Laboratory findings showed severe hypercalcemia (>18.0 mg/dL) and markedly elevated parathyroid hormone level (>2500 pg/mL). Sestamibi scan was negative. Surgical resection included left hemithyroidectomy and selective cervical lymphadenectomy (levels III–V). Intraoperative pathology confirmed PC. Histology revealed skeletal muscle invasion, necrosis, nuclear pleomorphism, fibrous bands, and two predominant histologic chief cell patterns: a necrotic solid epithelioid component and a spindled/sarcomatoid area invading muscle. All 32 resected lymph nodes were negative. Immunostaining was positive for parathyroid hormone and chromogranin, negative for TTF-1. The patient remains disease-free 27 months post-diagnosis. Results NA Conclusion This case highlights the diagnostic complexity of PC, the potential for neurologic presentations, and the importance of caution when dissecting lymph nodes, even if radiologically prominent. Clinicians should consider PC even with atypical imaging and presentation.