Primary hyperparathyroidism from parathyroid microadenoma: specific features and implications for a surgical strategy in the era of minimally invasive parathyroidectomy.

Background: The aim of this study was to identify the specific preoperative characteristics of patients with parathyroid microadenoma and to report their outcomes after surgical treatment.

Study Design: Parathyroid microadenomas (weight < 100 mg) were identified in 62 (6%) of the 1,012 patients operated on for a parathyroid adenoma between 1995 and 2004. Presentation and outcomes after surgery were compared with those of 124 patients operated on consecutively for parathyroid adenoma (>100 mg) during the last year of the study. All patients underwent bilateral surgical exploration of the neck. Success was defined as resection of a pathologic gland combined with normocalcemia at 6 months after operation. Logistic regression was used to test the relationship between groups and potential predictive factors of microadenoma.

Results: There were 57 women (92%) and the median age was 57 years (range 29 to 77 years). Median preoperative calcemia and parathyroid hormone (PTH) serum levels were 2.64 mmol/L (range 2.31 to 3 mmol/L) and 79 pg/mL (range 30 to 189 pg/mL), respectively. There was no difference in the clinical presentation between patients with microadenoma and adenoma. Preoperative calcium (p < 0.001) and PTH serum levels (p = 0.014) were significantly higher in patients with adenoma. Calcium and PTH serum levels lower than 2.6 mmol/L and 60 pg/mL, respectively, predicted the presence of microadenoma with respective specificities of 0.89 and 0.87. Success rates were similar in the microadenoma and adenoma groups (92% vs 98%; p = 0.11).

Conclusions: Mild preoperative elevations of calcium or PTH serum levels should warn about the risk of microadenoma. In this setting, intraoperative difficulties should be expected in identifying the pathologic gland, and bilateral neck exploration should be the preferred surgical approach.