Abstract
Functional parathyroid cysts are a rare cause of primary hyperparathyroidism and are often mistaken for thyroid cysts. Systemic lupus erythematosus (SLE) is also a very rare cause of hypercalcemia. We report the case of a 62-year-old woman, who was diagnosed with SLE 30 years ago, presenting with clinical and biochemical features of primary hyperparathyroidism. Laboratory investigation revealed increased serum calcium and parathyroid hormone (PTH) levels; neck ultrasonography (USG) revealed 40×34×26 mm cystic mass in the left lobe of thyroid gland. PTH level in the cysts was >2500 pg/ml, determined by USG-guided fine-needle aspiration (FNA). In this case, no evidence for potential pathogenic association between parathyroid cyst and SLE was uncovered. However, the recognition of this association is very important because the therapeutical strategy is completely different. Operative management is usually straightforward and alleviates symptoms and any biochemical abnormalities caused by the cyst. LEARNING POINTS: Functional parathyroid cysts are the rare cause of primary hyperparathyroidism and are often mistaken for thyroid cysts.SLE is also a very rare cause of hypercalcemia.Ultrasound-guided FNA of cystic fluid with assay for PTH level is an accurate method of differentiating parathyroid cyst from thyroid cyst.Appropriate management of functional parathyroid cysts is surgical excision.