Hyperparathyroidism

Hyperparathyroidism is overactivity of the parathyroid glands resulting in excess production of parathyroid hormone (PTH). The parathyroid hormone regulates calcium and phosphate levels and helps to maintain these levels. Excessive PTH secretion may be due to problems in the glands themselves, in which case it is referred to as primary hyperparathryroidism and which leads to hypercalcemia (raised calcium levels). It may also occur in response to low calcium levels, as encountered in various situations such as vitamin D deficiency or chronic kidney disease; this is referred to as secondary hyperparathyroidism. In all cases, the raised PTH levels are harmful to bone, and treatment is often needed. Recent evidence suggests that Vitamin D deficiency/insufficiency plays a role in the development of hyperparathyroidism. Lithium is associated with an increased incidence of hyperparathyroidism.

Primary
Primary hyperparathyroidism results from a hyperfunction of the parathyroid glands themselves. There is oversecretion of PTH due to adenoma, hyperplasia or, rarely, carcinoma of the parathyroid glands.

Secondary
Secondary hyperparathyroidism is the reaction of the parathyroid glands to a hypocalcemia caused by something other than a parathyroid pathology, e.g. chronic renal failure.

Tertiary
Tertiary hyperparathyroidism result from hyperplasia of the parathyroid glands and a loss of response to serum calcium levels. This disorder is most often seen in patients with chronic renal failure and is an autonomous activity.

Quartary and Quintary
Quartary and quintary are rare conditions that may be observed after surgical removal of primary hyperparathyroidism, when it has led to renal damage that now again causes a form of secondary (quartary) hyperparathyroidism that may itself result in autonomy (quintary hyperparathyoidism). . Additionally, quartary hyperparathyroidism may ensue from hungry bone syndrome after parathyroidectomy.

Symptoms and signs
Some may present without symptoms. Of those patients who do present with symptoms, they are commonly associated with the effects of an increased level of calcium. Since calcium is involved in trans-synaptic communication in the nervous system, high blood calcium levels have a direct effect on the nervous system. Thus, most of the symptoms of parathyroid disease are "neurological" in origin. Common manifestations of hyperparathyroidism include weakness and fatigue, depression, bone pain, muscle soreness (myalgias), decreased appetite, feelings of nausea and vomiting, constipation, polyuria, polydipsia, cognitive impairment, kidney stones and osteoporosis. Surgical removal of a parathyroid tumor will eliminate the symptoms in most patients.

Osteomalacia
Osteomalacia associated with hyperparathyroidism is caused by the high parathyroid hormone secreted by overactive parathyroid gland(s). Excess parathyroid hormone (PTH) acts indirectly on osteoclasts as they lack a PTH receptor. Instead, PTH stimulates osteoblasts, which in turn increases their expression of RANKL. RANKL is then able to bind osteoclasts which stimulates their activation which ultimately leads to the removal of calcium from the bones. Thus, the high calcium in the blood comes partly from the bones as well as from increased renal reabsorption. Removing the offending parathyroid gland will restore normal bone density over several years.

Intact PTH
In primary hyperparathyroidism, parathyroid hormone (PTH) levels will be either elevated or "inappropriately normal" in the presence of elevated calcium. Typically PTH levels vary greatly over time in the affected patient and (as with Ca and Ca++ levels) must be retested several times to see the pattern. The currently accepted test for PTH is "Intact PTH" which is intended to detect only relatively intact and biologically active PTH molecules. Older tests often detected other, inactive fragments. Even "Intact PTH" may be inaccurate in patients with renal dysfunction.

Serum calcium or Ionized Calcium (Ca++)
In cases of primary hyperparathyroidism or tertiary hyperparathyroidism heightened PTH leads to increased serum calcium (hypercalcemia) due to:
 * 1) increased bone resorption, allowing flow of calcium from bone to blood
 * 2) reduced renal clearance of calcium
 * 3) increased intestinal calcium absorption

Elevated ionized (Ca++) calcium may be a more reliable indicator of hyperparathyroidism.

By contrast, in secondary hyperparathyroidism effectiveness of PTH is reduced.

Serum phosphate
In primary hyperparathyroidism, serum phosphate levels are abnormally low as a result of decreased renal tubular phosphate reabsorption. However, this is only present in about 50% of cases. This contrasts with secondary hyperparathyroidism, in which serum phosphate levels are generally elevated because of renal disease.

Alkaline phosphatase
Alkaline phosphatase levels are usually elevated in hyperparathyroidism. In primary hyperthyroidism, levels may remain within the normal range, however this is 'inappropriately normal' given the increased levels of plasma calcium.

Technetium sestamibi
A sestamibi scan is a procedure in nuclear medicine which is performed to identify hyperparathyroidism (or parathyroid adenoma). It is used by surgeons to locate ectopic parathyroid adenomas, most commonly found in the anterior mediastianum.

Primary

 * The most common cause of primary hyperparathyroidism is a benign parathyroid adenoma that loses its sensitivity to circulating calcium levels. Usually, only one of the four parathyroid glands is affected.
 * A less common cause is from multiple endocrine neoplasia (MEN), either type 1 (caused by a mutation in the gene MEN1) or type 2a (caused by a mutation in the gene RET). Other mutations that have been linked to parathyroid neoplasia include mutations in the genes HRPT2, and CASR.

Secondary
Secondary hyperparathyroidism is due to excessive secretion of parathyroid hormone (PTH) by the parathyroid glands in response to hypocalcemia (low blood calcium levels) and/or hyperphosphatemia (high blood phosphate levels), usually due to chronic renal failure. The bone disease in secondary parathyroidism along with renal failure is termed renal osteodystrophy.

Patients with bipolar disorder who are receiving long-term lithium treatment are at increased risk for hyperparathyroidism. Elevated calcium levels are found in 15% to 20% of patients who have been taking lithium long-term. However, only a few of these patients have significantly elevated levels of parathyroid hormone and clinical symptoms of hyperparathyroidism. Lithium-associated hyperparathyroidism is usually caused by a single parathyroid adenoma.

Tertiary
Tertiary hyperparathyroidism, quartary and quintary hyperparathyroidism are rare forms that are caused by long lasting disorders of the calcium feedback control system. In cases of long-standing secondary hyperparathyroidism, the hypertrophied parathyroid glands can become autonomously functioning and continue to secrete PTH independent of whether the original stimuli to secrete PTH are still present.

Diagnosis
The gold standard of diagnosis is the Parathyroid immunoassay. Once an elevated Parathyroid hormone has been confirmed, goal of diagnosis is to determine whether the hyperparathyroidism is primary or secondary in origin by obtaining a serum calcium level:

Tertiary hyperparathyroidism has a high PTH and a high serum calcium. It is differentiated from primary hyperparathyroidism by a history of chronic kidney failure and secondary hyperparathyroidism.

Treatment and monitoring
Endocrinologists diagnose diseases affecting glands and should be consulted for hyperparathyroidism. Treatment for the three different types of hyperparathyroidism vary. Generally treatment is first and foremost directed at hypercalcemia; if symptomatic, patients are sent for surgery to remove the parathyroid tumor (parathyroid adenoma) or parathyroid gland (see hypercalcemia). Most experts now believe that almost all patients with hyperparathyroidism should be evaluated for surgery. If hyperparathyroidism is caused by a tumor, it will almost always progress as the tumor grows.

Testing for hyperparathryroidism:
 * Calcium level
 * Bone density
 * Vitamin D
 * Phosphorus

Calcimimetics
A calcimimetic (cinacalcet) is a new type of drug to be considered as a potential therapy for some people with primary and secondary hyperparathyroidism on dialysis. It is recognised by the body as if it is calcium, in other words, it mimics the effect of calcium in your tissues. This tricks your body into thinking there is more calcium in the blood which reduces PTH release from parathyroid glands, leading to lower calcium and phosphorus levels in your blood. Calcimimetics control PTH release from parathyroid glands without increasing calcium and phosphorus levels. The most common side effects of calcimimetics are mild or moderate nausea and vomiting.

History
Hyperparathyroidism was first described and treated in the 1930s by Fuller Albright of Massachusetts General Hospital, working at the Mallinckrodt General Clinical Research Center. The oldest known case was found in a cadaver from an Early Neolithic cemetery in southwest Germany.