Benign condition characterized by a proliferation of parathyroid cells, often in a nodule within the parathyroid gland. Parathyroid adenomas are often responsible for hyperparathyroidism, which leads to abnormal production of parathyroid hormone, resulting in hypercalcemia. When symptomatic, patients may present with constipation, nausea, muscle weakness, lethargy, memory impairment, and depressed mood.