Factors associated with negative ^99mTc-MIBI scanning in patients with primary hyperparathyroidism

The objective was to evaluate the clinical and biological factors associated with negative ^99mTc-MIBI scanning in patients with primary hyperparathyroidism (PHPT).

A retrospective observational study was designed in 195 patients (mean age: 59.2 ± 13.0 years; 77% woman) with PHPT (calcium: 11,3 ± 1,1 mg/dl and PTH: 218 ± 295 pg/ml) studied in endocrinology setting between 2013 and 2020. An univariate and multivariate analysis was made to evaluate the clinical and biological factors associated with negative ^99mTc-MIBI scanning.

50 patients (26%) with negative ^99mTc-MIBI scanning had lower PTH levels (146 ± 98 vs. 244 ± 334; p < 0,001), adenomas with smaller sonographic dimensions (maximum diameter: 1,2 ± 0,4 vs. 1,7 ± 0,9 cm; p = 0,001 and volume: 0,36 ± 0,43 vs. 1,7 ± 4,1 cm³; p < 0,001), localized more frequently in upper parathyroid glands (37% vs 14%; p = 0,005) and associated more frequently to thyroid nodules (72% vs 57%; p = 0,045) than patients with positive scanning. 116 patients were operated and parathyroid adenomas were smaller (maximum diameter: 1,3 ± 0,5 vs. 1,9 ± 1,1 cm; p = 0,008 and volume: 0,30 ± 0,20 vs. 1,2 ± 1,1 cm³; p < 0,001), less heavy (567 ± 282 vs. 1470 ± 1374 mgr.; p = 0,030) and were localized more frequently in upper situation (65% vs 16%; p < 0,001) than patients with positive scanning. In the multivariate analysis an independent association between negative ^99mTc-MIBI scanning and size of removed adenoma ≤1 cm (OR: 5,77; IC 95: 1,46-22,71) and upper adenoma localization were observed (OR: 8,05; IC 95%: 2,22-29,16).

One in four patients studied for PHPT had a negative ^99mTc-MIBI scanning and were independent associated with size of adenoma ≤1 cm and upper adenoma localization.