Parathyroid disorders can be classified by those that make the parathyroid glands more active (hyperparathyroidism) and those that make them less active (hypoparathyroidism).

Hyperparathyroidism is a condition in which the parathyroid glands produce excessive amounts of parathyroid hormone (PTH). PTH regulates the amount of calcium in the body. Excess PTH signals to the body that there is a calcium deficiency, triggering more calcium to be absorbed from food and extra calcium to be leached from the bones. In addition, PTH triggers the kidneys to release phosphorus into the urine and reduces its presence in the blood.

Complications of hyperparathyroidism can include kidney stones, osteoporosis, fractures, high blood pressure, pseudogout (a form of arthritis involving deposits of calcium crystals in joints), tendon ruptures, pancreatitis and stomach ulcers.

Hyperparathyroidism can be classified as “primary” or “secondary.” Primary hyperparathyroidism is more common and is due to enlarged, overactive parathyroid glands. Secondary hyperparathyroidism can result from chronic kidney failure (end-stage renal disease) or other medical conditions that cause the parathyroid glands to become overactive. Roughly 100,000 Americans develop some form of hyperparathyroidism each year, according to the National Institutes of Diabetes and Digestive and Kidney Diseases (NIDDK).

Hypoparathyroidism is a rare condition in which the parathyroid glands produce too little PTH. This causes hypocalcemia, an insufficient level of calcium in the blood. In addition, the amount of phosphorus in the blood increases.

Hypoparathyroidism is usually classified as being hereditary or acquired. Patients with hereditary hypoparathyroidism may have been born with absent or dysfunctional parathyroid glands. This defect is usually detected early in life when symptoms of hypoparathyroidism appear. Acquired hypoparathyroidism may occur after injury or surgery to the neck area. There are also certain diseases that can result in hypoparathyroidism.

Hypoparathyroidism can impair function of the muscles and nerves. However, most of the complications associated with hypoparathyroidism are reversible with treatment. Children who are born with hypoparathyroidism may experience stunted growth or mental retardation, which may not be reversible.

Pseudohypoparathyroidism is an inherited condition that causes symptoms similar to hypoparathyroidism. Patients with pseudohypoparathyroidism have fully functioning parathyroid glands that produce PTH. However, the body becomes resistant to PTH and cannot use it efficiently, resulting in symptoms of hypoparathyroidism.