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 ankle joints extended — the so-called carpopedal spasm. Spasm of the muscles of respiration results in not only pain and stridor, but also dread of suffocation. In infancy, the symptoms of tetany may be mistaken for epilepsy, although there is no loss of consciousness.

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.