Primary hyperparathyroidism - Disorders of the parathyroids

Primary hyperparathyroidism

Definition

Primary oversecretion of parathyroid hormone (PTH) by the parathyroid glands.

Incidence/prevalence

Common amongst middleaged and elderly. In patients over the age of 40, incidence may be as high as 1 in 1000 to 1 in 2000.

Age

Increases with age.

Sex

2–4F : 1M

Aetiology

Neoplasia of the parathyroid gland(s). There are thought to be genetic and environmental predisposing factors including a family history of Multiple Endocrine Neoplasia and neck irradiation.

Single benign adenoma 75%

Multiple adenomata or hyperplasia 24% Parathyroid carcinoma 1%

Pathophysiology

Autonomous hypersecretion from one or more glands result in hyperparathyroidism, with hypercalcaemia, hypophosphataemia and osteoporosis.

Clinical features

Presentation ranges from asymptomatic (diagnosed incidentally on a calcium measurement) to severe and life-threatening hypercalcaemia. Patients commonly remain asymptomatic for many years, then develop insidious weakness, fatigue, anorexia, thirst, constipation and confusion.

Bones: Increased calcium resorption, classically causes bone cysts (osteitis fibrosa cystica) which may present with diffuse pain or rarely fractures.

Stones: Urinary stones and nephrocalcinosis (calcification of the kidney), due to hypercalciuria. Hypertension is common, possibly due to renal damage.

Groans: Abdominal symptoms such as nausea, vomiting, pain and constipation.

Moans: Psychosis, confusion and drowsiness.

Complications

Fractures, complications of urinary stones, seizures, coma, sudden death due to cardiac arrest. Dehydration occurs secondary to hypercalcaemia, which can cause a nephrogenic diabetes insipidus.

Investigations

Serum calcium, PTH and albumin levels (for corrected calcium) should be measured. If hypercalcaemia is found, and PTH is detectable the likely diagnosis is primary or tertiary hyperparathyroidism. In other causes of hypercalcaemia, PTH is suppressed to be-low detectable values.

Ultrasound of the neck may be able to differentiate between parathyroid adenoma or hyperplasia. The tumour(s) may be located by technetium-thallium subtraction scanning or selective venous catheterisation to assay PTH and find the source.

Management

Surgery is the only curative option. The parathyroids are exposed by a transverse neck incision. Each lobe of the thyroid is mobilised and the parathyroids identified. Abnormal glands are removed and frozen sections examined. If all four glands are enlarged, all but a portion of one gland is removed.

If symptomatic, treatment should be directed at correcting the hypercalcaemia with fluids. If Ca >3.5 mmol/L, the patient is vomiting, pyrexial or there are severe symptoms or signs such as confusion, intravenous saline together with iv furosemide are used. Potassium and magnesium often fall and need supplements. Bisphosphonates may also be used, although they can take some time to act.

If surgery is not possible, oral phosphates or bispho-sphonates reduce bone resorption and osteoclast activity.