Hyperparathyroidism is a condition in which excess parathyroid hormone is produced, disrupting the normal balance of calcium, phosphate and vitamin D in the body. The excess parathyroid hormone (Pth) may be primary, secondary to other conditions, or autonomous (from an independent source).
Risk factors and associated conditions
In most cases, a specific cause cannot be identified.
Hyperparathryoidism affects women twice as often as it does men, the incidence rising with age. Vitamin D deficiency, malabsorption states, a positive family history and some rare genetic disorders also increase the risk of developing hyperparathyroidism.
Previous radiation to the neck has been implicated in some patients.
Long-term use of medications, such as lithium and thiazide diuretics can cause a mild increase in Pth levels, which may persist even when the drug is stopped.
PTh, essential for life, is normally produced by the parathryroid glands. These are four, pea-sized glands, one located in each “corner” or pole, of the thyroid gland. The action of Pth is to maintain normal blood calcium levels and to help in the manufacture of active vitamin D. Active vitamin D also plays a role in calcium regulation.
Pth is known to act mainly on the bones and kidneys, where it exerts most of its effects. Other tissues are also influenced by Pth, notably breast, heart, skin, blood vessels and pancreas. The main effect of Pth is to raise blood calcium levels by releasing stored calcium from bone. When these are depleted, bone is broken down and resorbed to release the calcium and phosphates used in its original manufacture. Re-absorption of calcium from the intestine is also increased. The kidney is also directly stimulated to reabsorb calcium and phosphate from urine, minimising potential losses. The production of vitamin D is stimulated, which interacts with Pth in the overall management of calcium and phosphates.
Calcium is essential for muscle contraction, blood clotting, nerve function and the regulation of hormone secretions. Effective control is thus needed for many basic functions. Phosphorus (usually in phosphate form) is also essential, and closely linked to calcium movements, bone metabolism, and sources of energy for the whole body.
Symptoms and signs
Excess Pth results in raised calcium and phosphate levels, which causes both general, non-specific symptoms, and some which are directly related to the organs affected by changes in these levels.
General symptoms usually arise slowly and include vague body aches, fatigue and weakness.
Specific symptoms and signs related to high calcium levels include:
- Abdominal pain - often linked to peptic ulcers/pancreatitis - high calcium levels cause increased stomach acid production,
- Nausea, vomiting,
- Loss of appetite,
- Hypertension and heart failure,
- Increased thirst and urination,
- Kidney stones in 15-20 percent due to high urinary calcium,
- Specific muscular weakness,
- Thinning of bones - may lead to fractures, and
- Mental confusion and memory loss.
To confirm clinical findings, and locate the abnormal gland/s, test needed are
- Blood Pth levels,
- 24-hour urine collection - for renal function and calcium excretion,
- Bone mineral density scan - to assess bone strength and risk of fractures,
- X-rays or ultrasound - to check for kidney-stones, and
- Radio-scans to locate the overactive parathryroid gland/s.
Underlying causes for Secondary hyparathryoidism must be identified and treated: this usually resolves the hormone problem. Chronic kidney disease is often the cause, with inadequate vitamin D production. Vitamin D is easily given as a supplement, but becomes less effective after a time. Cinacalcet may be tried (under strict supervision) for these patients, provided they are not on regular dialysis.
For Primary cases, surgery remains the most effective option. If tests identify one or more abnormal glands, only these are removed. If no single overactive gland is found, then three of the four glands are removed, leaving one intact to provide at least some natural hormone to regulate calcium and phosphate. Apart from those for any operation, there are some specific risks involved in this surgery (such as damage to the vocal cords’ nerve supply, and removing too much parathyroid, causing a deficiency state, which will need immediate treatment).
(Dr AG Hall)