Hypoparathyroidism
Parathyroid tetany, due to hypocalcaemia, is a
rare complication of subtotal thyroidectomy (less than 1 per cent) but a more
common complication of total thyroidectomy. At these operations, some of the
parathyroid glands may be removed or have their blood supply temporarily embarrassed.
It may also occur after surgery to the parathyroids themselves. Symptoms usually
appear on the second or third postoperative day, and are temporary. Milder forms
of hypoparathyroidism have been described in the follow-up of thyroidectomised
patients. Permanent hypoparathyroidism, most commonly encountered following
radical thyroidectomy for cancer, requires constant supervision and treatment.
Tetany in the newborn may occur within the first few days of life in the child
born of a mother with undiagnosed hypoparathyroidism.
Spontaneous
hypoparathyroidism is an unusual form of autoimmune disease.
Clinical
features
The first symptoms are tingling and numbness
in the face, fingers and toes. In extreme cases, cramps in the hands and feet
are very painful; the extended fingers are flexed at their metacarpophalangeal
joints, with the thumb strongly adducted (Fig. 45.3); the toes are
plantar-flexed and the
Latent
tetany may be demonstrated by the following.
• Chvostek’s sign. Tapping over the branches of the facial nerve at the
angle of the jaw will produce twitching at the corner of the mouth, the ala of
the nose and the eyelids.
• Trousseau’s sign. A sphygmomanometer cuff applied to the arm and
inflated above the systolic blood pressure for not more than 2 minutes will
produce carpal spasm.
Treatment
In acute cases the symptoms may be relieved
speedily by the slow intravenous injection of 10—20 ml of a 10 per cent
solution of calcium gluconate. This may be repeated until the patient’s
circulating calcium level has been stabilised. For longer-term management, the
absorption of calcium is enhanced by oral administration of the most active
metabolite of vitamin D — 1,25-dihydroxycholecalciferol [1,25(OH)2D3].
Its major action is on the gut, promoting active absorption of calcium and
phosphorus, raising calcium levels to normal within a week. Magnesium
supplements may occasionally be needed. Serum calcium levels must be estimated
daily and the dosage adjusted as appropriate.