Primary hyperparathyroidism: fifth parathyroid intrathymic adenoma in a young patient.

The clinical case described in this paper deals with a young female patient affected by primary hyperparathyroidism caused by an ectopic parathyroid adenoma of a supernumerary intrathymic parathyroid. The patient had hypercalcemia, in association with increased levels of parathormone, but was otherwise asymptomatic. Genetics tests for mutation of the MEN1, HRPT2, and CaSR genes were negative. She therefore underwent laboratory and instrumental tests but localization results in the neck were negative--only an intrathymic nodule was visualized. The complete surgical ablation of the thymus was conducted, which highlighted a nodule that, at histological examination, was shown to be an adenoma of a fifth parathyroid gland. The existence of a fifth, hyperfunctioning, intrathoracic parathyroid appears to be a rare cause of primary juvenile sporadic hyperparathyroidism. This peculiar clinical case could be of interest in similar cases evaluated by other surgeons.