Oxyphil Cell Parathyroid Adenomas Causing Primary Hyperparathyroidism: a Clinico-Pathological Correlation.

Oxyphil cell parathyroid adenomas (OPA) are considered to be an uncommon cause of primary hyperparathyroidism (PHPT), and were historically thought to be clinically silent. It has been our clinical impression that these adenomas present more often than previously thought and may manifest a more severe form of primary hyperparathyroidism than classical adenoma. The aim of this study was to describe the incidence and clinical presentation of OPA. An observational case-control study was undertaken. The study group comprised patients undergoing parathyroidectomy for PHPT where the final pathology confirmed OPA. The controls were made up of an age- and sex-matched group of patients having parathyroidectomy in the same time period where the final pathology confirmed a classical or non-oxyphil adenoma. OPA were defined as parathyroid tumours containing >75% oxyphilic cells. The OPA cases were obtained by reviewing all histopathology slides over an 11-year period (2002-12) where the reports contained the words 'oxyphil' or 'oxyphilic' parathyroid adenomas. These were then reviewed by two independent pathologists to confirm a diagnosis of OPA. The primary outcome measures were preoperative serum calcium and parathyroid hormone (PTH) levels. Secondary outcome measures were symptoms at presentation, accuracy of preoperative localization studies, parathyroid gland weight following surgery, and type of surgery undertaken. In the period 2002-2012, 2739 patients underwent surgery for PHPT. Following pathological review, 91 cases were confirmed as being OPA and formed the study group. A control group (n = 91) from the same period was selected following matching on the basis of age at presentation and sex. OPA were associated with higher preoperative serum calcium (10.84 versus 10.48 mg/dL, p < 0.001) and parathyroid hormone (139 versus 64 ng/L, p < 0.001). At presentation, a lower proportion of OPA cases had asymptomatic disease (15 versus 29%, p = 0.03). There was a trend toward a higher rate of renal calculi at presentation in the OPA group (9 versus 3%, p = 0.07). Preoperative ultrasound was less accurate in localization of OPA when compared with classical adenoma. The rate of minimally invasive surgery was 67% for OPA and 78% for the control group (p = 0.06). All patients were cured of hypercalcaemia at 6-month follow up. There was no significant difference in the weight of removed parathyroid tissue between the groups (868 mg for OPA versus 789 mg for the control group, p = 0.6). OPA are frequently symptomatic and are associated with higher preoperative serum calcium and parathyroid hormone levels than classical types of parathyroid adenomas. OPA are less likely to be localised on preoperative ultrasound examination.