Primary hyperparathyroidism is hyperfunction of the parathyroid glands resulting in overproduction of parathyroid hormone (PTH), which causes elevated blood calcium levels (see hypercalcemia). Primary hyperparathyroidism is caused by parathyroid adenoma, parathyroid hyperplasia, and parathyroid carcinoma (in rare cases).

High-risk populations include postmenopausal women and patients who have had chronic and serious calcium or vitamin D deficiency, have a rare genetic disease, have undergone radiation therapy, or have taken lithium.

The disorder is most prevalent in individuals between 50 and 60 years of age. Females are more frequently affected.

Patients are usually asymptomatic. Symptomatic patients have variable presentations. In mild cases, common symptoms include fatigue, lethargy, depression, muscle weakness, and muscle pain. In severe cases, symptoms include anorexia, nausea, vomiting, constipation, confusion, memory impairment, frequent urination, and bone thinning and fractures. Sustained hyperparathyroidism can lead to osteitis fibrosa cystica, forming cystlike tumors in the bones.

Complications are dependent on the long-term effects of insufficient calcium in a patient's bones and excessive calcium circulating in the bloodstream. Common complications include osteoporosis, kidney stones, cardiovascular disease, and hypoparathyroidism of the neonate in pregnant individuals with untreated hyperparathyroidism.

Treatment is dependent on the course of the disease and will vary depending on individual cases. Patients who are asymptomatic may not require any treatment and should be closely monitored by their physicians. Medications such as bisphosphonates may help with bone health, and estrogen therapy may benefit postmenopausal women. Patients with primary hyperparathyroidism due to familial hypocalciuric hypercalcemia may need parathyroidectomies.