The patient's technetium 99m-sestamibi scan showed normal uptake in the thyroid gland 20 minutes after administration of the radioisotope. Two hours after administration, once the radioisotope had "washed off" of the thyroid glands, uptake was noted in the left inferior parathyroid area, which is consistent with a parathyroid adenoma (see Figures 1 and 2).
His serum parathyroid hormone concentration was found to be markedly elevated at 450 pg/mL (450 ng/L; reference range, 10-60 pg/mL), confirming the diagnosis of primary hyperparathyroidism.
About 83% of people have four parathyroid glands: two superior glands and two inferior glands. Approximately 13% have more than four glands, whereas 3% have only three glands. The position of the superior glands is fairly constant; ectopic sites are usually seen with the inferior glands but not with the superior glands. The normal thyroid glands are encapsulated, soft, ovoid, yellowish-white organs that are surrounded by fat; each gland weighs approximately 40 mg and measures about 5 x 3 x 1 mm. The branches of the paired inferior thyroid arteries supply most of their blood. They receive blood from the paired superior thyroid arteries, the thyroidea ima artery, and branches of the laryngeal and tracheoesophageal arteries as well.[1,2]
The parathyroid glands secrete parathyroid hormone (PTH), which regulates serum calcium and phosphorus levels by raising serum calcium levels while lowering the serum phosphorus concentration. The regulation of PTH secretion occurs through a negative feedback loop; calcium-sensing receptors on the membranes of the parathyroid gland cells decrease PTH production as serum calcium concentrations rise. Hypocalcemia can prompt rapid secretion of the preformed PTH hormone. Extracellular calcium interacts with a calcium sensor to control PTH secretion; stimulation of the receptor by high calcium levels suppresses PTH secretion. The receptor is present in the parathyroid glands, the calcitonin secreting cells (C cells) of the thyroid, the brain, and the kidneys.[1,3]
Primary hyperparathyroidism is characterized by an excess of PTH secretion. Primary hyperparathyroidism affects approximately 1 person per 500-1000 population. It is two to four times more common in women than in men. It most commonly affects middle-aged adults and is rarely seen in children. Primary hyperparathyroidism is primarily caused by solitary adenomas (80% of cases) and, less commonly, chief cell hyperplasia (15%), multiple endocrine neoplasia (<5%), and parathyroid carcinoma (rare).
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