Hypoparathyroidism
A deficiency of parathyroid hormone (PTH) characterised by hypocalcaemia and hyperphosphataemia, with normal renal function.
Most commonly occurs following surgery with removal of abnormal parathyroid glands or removal of neck malignancies. Gland failure may be caused by direct damage to the glands or their blood supply.
· Genetic abnormalities are usually autosomal recessive and manifest at an early age. Associated with autoantibodies specific for parathyroid and adrenal tissue.
· Associated autoimmune syndromes include pernicious anaemia, ovarian failure, autoimmune thyroiditis, and diabetes mellitus.
· Late onset idiopathic hypoparathyroidism occurs
without circulating autoantibodies.
Functional hypoparathyroidism occurs in patients with chronic hypomagnesaemia which results in a failure of PTH release.
PTH is normally released in response to hypocalcaemia, to restore calcium levels. The consequences of reduced PTH are decreased calcium levels, increased phosphate levels, decreased 1,25(OH)2D3 and alkalosis (due to decreased bicarbonate excretion).
· In chronic cases of hypoparathyroidism, calcification of the basal ganglia causing extrapyramidal signs and calcification of cornea may occur.
· Cardiovascular problems with prolongation of the QT interval in ECGs associated with hypocalcaemia, hypotension and refractory congestive heart failure.
Hypocalcaemia and alkalosis cause increased neuromuscular excitability: paraesthesias of the fingertips and toes, tetany (spasms of muscles of extremities and face)
· Trousseau’s sign: Inflating a blood pressure cuff to above systolic BP for at least 2 minutes causes carpal spasm, which does not relax for a few seconds after deflation.
· Chvostek’s sign: Tapping the facial nerve anterior to the ear lobe causes twitching of the facial muscles.
· Convulsions occur more commonly in young people.
Low calcium with normal or high phosphate with no detectable PTH on immunoassay. Alkaline phosphatase is normal. U&Es should be normal, or a renal cause is suspected.
Replacement therapy with 1,25(OH)2D3 (calcitriol, vitamin D2) or 1(OH)D3. Serum and urinary calcium must be measured, as hypercalcaemia and hypercalciuria can occur. Vitamin D intoxication causes irreversible renal damage. Thiazide diuretics which increase renal tubular reabsorption of calcium may be useful in treating hypercalciuria.
Lifelong treatment and follow-up.
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