Hyperparathyroidism occurs when there is an excess of parathyroid hormone (PTH) being secreted from the parathyroid glands in the neck. It is a prevalent condition seen in both primary and secondary care as primary hyperparathyroidism is the most common cause of hypercalcaemia.
The parathyroid glands sit in the neck, on the posterior surface of the lateral lobes of the thyroid. Most adults have four, which are commonly described in two pairs (the superior and inferior parathyroid glands), although their positions in the neck can be highly variable.
Normally, the role of the parathyroid glands is to regulate serum calcium and phosphate levels via the secretion of PTH. The chief cells of the parathyroid glands are responsible for the synthesis and secretion of PTH, as well as the sensing of changes in serum calcium levels via the calcium-sensing receptor.
In response to hypocalcaemia, secretion of PTH is increased. PTH then raises serum calcium levels by acting on various organs throughout the body:
The subsequent rise in serum calcium then reduces PTH secretion, an example of a negative feedback loop.
In hyperparathyroidism, the homeostatic mechanism of PTH secretion becomes decompensated, resulting in an inappropriately high secretion of PTH. There are several causes for this, leading to three different sub-types of hyperparathyroidism.
Primary hyperparathyroidism is the most common of the three types and is driven by a pathology of the glands. One or more of the parathyroid glands is over-secreting PTH despite normal serum calcium, which over time leads to hypercalcaemia. Its aetiology can be adenoma (85%), hyperplasia (14%, may be associated with other conditions such as multiple endocrine neoplasias), or carcinoma (<1%).
Secondary hyperparathyroidism is due to a disorder in calcium-phosphate-bone metabolism. In response to low serum calcium levels as a result of another condition, commonly chronic kidney disease or vitamin D deficiency, the parathyroid glands secrete PTH. This may or may not normalise serum calcium levels, depending on the underlying condition.
Tertiary hyperparathyroidism may occur following a prolonged period of secondary hyperparathyroidism. In response to chronic PTH secretion, the glands may become hyperplastic and begin to secrete PTH autonomously. This can lead to hypercalcaemia as in primary hyperparathyroidism, especially if the underlying condition impairing calcium metabolism is treated.
Table 1. A summary of the differences between the types of hyperparathyroidism
Most primary hyperparathyroidism is sporadic. Risk factors include being a post-menopausal woman, having previous radiation exposure to the neck, and taking lithium.
Primary hyperparathyroidism may be associated with inherited disorders such as MEN. Secondary and tertiary hyperparathyroidism are associated with conditions affecting calcium metabolism, such as chronic kidney disease.
Primary hyperparathyroidism is usually asymptomatic and picked up incidentally on blood tests. However, when symptoms appear they are usually non-specific and related to the hypercalcaemia, regardless of the cause. Common symptoms include fatigue, polyuria, polydipsia, constipation, abdominal pain, vomiting, confusion, depression, and bone pain. Renal stones may also be observed, suggesting chronic hypercalcaemia.
Abdominal and bony tenderness may be found upon examination, but clinical signs of hypercalcaemia are typically absent.
The differential diagnoses for primary hyperparathyroidism are the other causes of hypercalcaemia. Malignancy is especially important to consider as it is the second most common cause of hypercalcaemia. The serum PTH is useful for distinguishing between primary hyperparathyroidism and malignancy, and for classifying other causes of hypercalcaemia into PTH-dependent and PTH-independent categories (see Table 2).
Hyperparathyroidism can be divided into two categories, depending on whether the parathyroid hormone (PTH) is raised or low-normal. These are known as PTH-dependent (↑ or high-normal PTH) and PTH-independent (↓ or low-normal PTH).
PTH-dependent causes of hyperparathyroidism include:
PTH-independent causes of hyperparathyroidism include:
Relevant laboratory investigations include:
Corrected calcium is also referred to as albumin-adjusted serum calcium. This is used because only 50% of serum calcium is in the free ionised form, which is biologically active. 40% is bound to proteins such as albumin while 10% is bound to anions. Thus, serum calcium without correction can be spuriously abnormal in those with albumin abnormalities. NICE recommend that direct ionised calcium testing should not be used to diagnose hyperparathyroidism.
Other relevant specialist laboratory investigations may include a 24-hour urinary calcium excretion test or calcium: creatinine clearance ratio to exclude familial hypocalciuric hypercalcaemia (FHH).
Relevant imaging investigations include:
Acute, severe hypercalcaemia of any cause requires urgent management in secondary care including the administration of intravenous fluids. An intravenous bisphosphonate such as pamidronate may also be indicated.
Mild primary hyperparathyroidism may not require any management other than monitoring symptoms and complications. This includes annual tests for corrected calcium and creatinine or eGFR, as well as assessing cardiovascular and fracture risk.
Medical management includes bisphosphonates, which do not affect serum calcium but do preserve bone density and reduce fracture risk; and cinacalcet (a calcium-sensing receptor agonist), which reduces PTH secretion and serum calcium.
Hyperparathyroidism occurs when there is an excess of parathyroid hormone (PTH) being secreted from the parathyroid glands in the neck.
Primary hyperparathyroidism is the most common cause of hypercalcaemia and often presents with mild, non-specific symptoms and may be detected incidentally. It is important to exclude other causes of hypercalcaemia, such as malignancy. In the first instance, a serum PTH with paired corrected calcium is the investigation of choice.
Primary hyperparathyroidism may be treated conservatively, with surgical management or with medications such as cinacalcet. It is used in patients with primary hyperparathyroidism in whom surgery would not be appropriate, has been declined or has been unsuccessful.
Secondary hyperparathyroidism should be managed by treating the underlying cause. Cinacalcet may be used for patients in whom this fails or who are on dialysis. Phosphate binders and calcium/vitamin D supplements may also be used, for example in chronic kidney disease.
Tertiary hyperparathyroidism may also be treated with surgical intervention (partial parathyroidectomy). Sometimes residual parathyroid tissue is reimplanted elsewhere in the body (e.g the forearm), where it is more accessible if future problems arise.
Curative therapy requires surgery (e.g. parathyroidectomy) and a referral can be considered for patients with confirmed primary hyperparathyroidism. NICE guidelines recommend referring for surgical management if:
Complications of surgery include hypocalcaemia, hoarseness and cough due to damage to the recurrent laryngeal nerve, bleeding, infection, or failure of surgery.
Complications of primary hyperparathyroidism include osteoporosis, renal impairment and calculi, pseudogout, pancreatitis and cardiovascular disease.
Hyperparathyroidism is a condition where the parathyroid gland is overactive. It causes an excessive amount of parathyroid hormone, which can lead to damage to bones, kidney stones, and other potential complications. Symptoms may include fatigue, tenderness in the neck or rib area, excessive thirst, and increased urination.
The primary cause of hyperparathyroidism is usually a benign (non-cancerous) tumor in one of the parathyroid glands. Other causes may include familial hypocalciuric hypercalcemia, multiple endocrine neoplasia (MEN), and vitamin D deficiency.
The diagnosis of hyperparathyroidism is based on physical examination, laboratory tests, imaging studies, and biopsy.
Management of hyperparathyroidism depends on the severity of the condition and the complications present. Medical treatments include medications to reduce parathyroid hormone, vitamin D supplements, and calcium supplements. Surgery is another option to remove the enlarged parathyroid gland.
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