Endocrine Abstracts

Introduction: Parathyroid cysts constitute a rare cause of primary hyperparathyroidism (PHPT). PHPT may also rarely coexist with non-medullary thyroid carcinoma (NMTC).

Case presentation: A 70-year old woman was admitted to our department for type 2 diabetes mellitus (T2DM) management. She also reported nephritic colics due to kidney stone disease. There were no reports for fractures, symptoms of hypercalcemia or obstructive neck symptomatology. Laboratory investigation for nephrolithiasis showed elevated serum total calcium and parathyroid hormone (PTH) concentrations: 10.8 mg/dl (corrected calcium, normal range: 8.4–10.4) and 187 pg/ml (normal range: 10–53). Serum phosphorus, magnesium and 25-hydroxy-vitamin D levels were low: 2.34 mg/dl (normal range: 2.5–4.5), 1.7 mg/dl (normal range 1.9–2.5) and 9 ng/ml (sufficiency levels >30), respectively. Renal function was normal (estimated glomerular filtration rate (eGFR): 144.3 ml/min/1.73 m²), as were the 24-h urinary calcium concentrations 189 mg/24-h (normal range: 50–300). Dual-energy X-ray absorptiometry (DXA) in lumbar spine was indicative of osteopenia (T-score: −2.3). Renal ultrasound was negative for the presence of kidney stones. Primary (PHPT) combined with secondary hyperparathyroidism was diagnosed and the patient underwent a neck ultrasound and parathyroid scintigraphy (Sestamibi) scan, which were indicative of a cystic mass attached to the lower pole of the right thyroid lobe with an estimated maximum diameter of 6.5 cm. Multinodular goitre was also diagnosed with some of the nodules being suspicious for malignancy. The patient underwent an uneventful right parathyroidectomy and total thyroidectomy. Post-operative corrected calcium and PTH levels were 9.3 mg/dl and 17 pg/ml. Histopathological diagnosis was also positive of a unifocal papillary thyroid carcinoma (PTC) of follicular variant, 6 mm in diameter, without extrathyroidal extension. Due to the patient’s low risk of PTC recurrence, no radioiodine was administered. The patient remains normocalcemic (with normal PTH levels and vitamin D sufficiency) and no signs of PTC recurrence two years after.

Conclusions: Functioning parathyroid cysts constitute a rare cause of PHPT. Large parathyroid cysts may be asymptomatic. PTC may rarely coexist with PHPT but it is not known if this is just a diagnosis of coincidence or a result of common pathogenetic mechanisms.