Endocrine Abstracts

Aim: To study those factors which influence the sensitivity and positive predictive value of combined MIBI scintigraphy and ultrasound scan in the localisation of parathyroid adenomas.

Method: A retrospective review of notes was done of 150 patients with hypercalcaemia referred to the Endocrine outpatients’ clinic, between the years 2002–2005.

Notes of 135 patients with biochemical evidence of primary hyperparathyroidism (PHT) were studied.

Results: The median age of the study group was 68 years and 76% were females. Forty percent of the patients were symptomatic at the time of diagnosis. The median adjusted calcium and PTH levels at the time of diagnosis were 2.79 mmol/l and 11.85 pmol/l, respectively. (Ref. ranges 2.20–2.65 mmol/l and 1.6–6.9 pmol/l, respectively). Sixty-one percent (83/135) of patients with biochemical PHT showed evidence of parathyroid lesion using combined MIBI scintigraphy and US scan. Concomitant thyroid nodular disease was present in 21%. Pre-scan calcium level but not PTH was significantly (P<0.005) higher in patients who showed parathyroid lesions on scans.

58/135 (43%) of patients with biochemical evidence of PHPT underwent surgery. Radiological diagnosis was the same as the histological diagnosis in 52/58. The sensitivity and PPV of combined scintigraphy and USS was 96.4 and 98.1%, respectively. The sensitivity in presence of thyroid nodular disease was 75% and in absence of thyroid disease was 100%.

Summary: MIBI scintigraphy and USS when used together are reliable to localise the parathyroid lesion pre-op with high sensitivity and PPV but results are influenced by the presence of nodular thyroid disease and low serum calcium concentration.

Conclusion: Negative scan results in the presence of nodular thyroid disease and/or low serum calcium levels must be treated with caution.