Tetany: causes, symptoms and treatment

Tetany is a collection of signs rather than a disease in its own right. It describes muscle twitching, cramping and spasm caused by nerves firing too easily. Calcium helps keep nerves and muscles stable. The NHS explains that calcium is a mineral the body needs to keep bones, muscles and nerves working properly.

When the level of calcium in the blood falls, nerves become irritable. Patient.info says that the ionised, or unbound, fraction of calcium is the part that matters physiologically, and that low calcium interferes with the function of many cells, nerve and muscle cells in particular. Magnesium also matters. Patient.info says that low magnesium must be corrected before low calcium will resolve.

Not all tetany is from low calcium. Overbreathing can make the blood more alkaline and add to tingling and spasm. Patient.info notes that tetany usually occurs after a rapid fall in calcium, together with respiratory alkalosis.

Patient.info says symptoms generally correlate with how big and how fast the fall in calcium is. A mildly low level of 2.00 to 2.12 mmol/L can cause no symptoms, while life-threatening problems can develop in severe hypocalcaemia below 1.9 mmol/L. The usual laboratory normal range is about 2.1 to 2.6 mmol/L, though ranges vary slightly.

The NHS lists a tingling or burning sensation in the fingers, toes and face, muscle pain, stiffness and spasms, tummy pain, brittle nails, dry hair and skin, and cataracts as symptoms of hypoparathyroidism. Less common and more serious symptoms include confusion, an irregular heartbeat and seizures.

Doctors look for particular signs. Patient.info describes carpopedal spasm, Chvostek's sign (tapping the facial nerve in front of the ear makes the facial muscles twitch), prolongation of the QT interval on the heart tracing, and spasm of the voice box or airways. After prolonged low calcium, changes include cataract, abnormal teeth and calcium deposits in the brain.

• Tingling or burning around the mouth, in fingers and toes

• Muscle cramps, pain, stiffness and spasm

• Hands drawn into a claw-like position

• Anxiety, low mood or irritability

• Confusion, irregular heartbeat or seizures in severe cases

• Noisy breathing or breathing difficulty from airway spasm

Patient.info divides causes of hypocalcaemia into those with low parathyroid hormone and those with high. Low parathyroid hormone, or hypoparathyroidism, is most often caused by surgery. It can also follow an autoimmune condition, an abnormal development of the glands in some genetic disorders, or damage from radiation or infiltration. The NHS adds Addison's disease and some rare genetic conditions.

With high parathyroid hormone, the cause is usually outside the glands. Patient.info lists vitamin D deficiency from low intake, malabsorption, little sun, or liver or kidney disease, and chronic kidney disease. Other causes include low or high magnesium, some drugs such as bisphosphonates, denosumab, cinacalcet and cisplatin, acute pancreatitis, a massive blood transfusion and tumour lysis after chemotherapy.

Patient.info reports that low calcium is extremely common in hospital inpatients and tends to track with severity of illness, and that it may be a marker of illness rather than a cause.

The key test is a blood calcium level, adjusted for albumin. Patient.info says to ensure an adjusted value is used and notes that prolonged tourniquet use can affect results. Further blood tests include kidney function, magnesium, phosphate, parathyroid hormone and vitamin D. An ECG checks for rhythm disturbance and a prolonged QT interval.

The NHS says that if you have neck or head surgery, these tests may be done soon after, to check whether the parathyroid glands were damaged. If calcium is very low or you have symptoms, Patient.info says admission is needed for further tests, whereas tests can often be done in primary care if there are no acute concerns.

A doctor will decide which tests are needed and whether overbreathing is part of the picture.

The treatment is aimed at the cause. For severe or symptomatic low calcium, Patient.info describes admission for urgent treatment with calcium given slowly into a vein, with repeated checks of the blood level. The NHS says the same for complications such as seizures and serious heart problems in hypoparathyroidism: calcium through a tube into a vein until the level returns to normal.

For longer-term problems, the NHS says hypoparathyroidism can be treated with calcium and vitamin D supplements, usually for life. You may be offered supplements even without symptoms if tests show damage to the glands. Diet changes include foods high in calcium such as dairy, green leafy vegetables, soy and tofu, and cutting down on red meat and starchy foods like pasta and white bread. Regular blood tests check the level, and extra medicines may be added if supplements are not working well.

Vitamin D deficiency is treated by correcting the deficiency. Magnesium is replaced if low. Patient.info says some people with hypoparathyroidism can have permanently unstable calcium levels and should remain under an endocrinologist.

Outlook depends on the cause. After thyroid or neck surgery the fall in calcium may be temporary or permanent. Patient.info reports that transient low calcium after thyroidectomy varies from about 7% to 49%, and permanent low calcium from 0.4% to 33%, across studies.

Once calcium is stable on treatment, symptoms should settle. Regular monitoring continues because both too little and too much calcium cause problems. The NHS says that if your calcium level becomes too low, it can cause seizures and serious heart problems, which is why blood tests are scheduled regularly and why symptoms should not be ignored.

The NHS says to call 999 if someone is having a seizure and it is the first time, it lasts longer than is usual for them or longer than 5 minutes if you do not know how long their seizures usually last. See a GP if you think you might have hypoparathyroidism. If you recently had neck or head surgery, try the contact details you were given first.

Call 999 or go to A&E for difficulty breathing, noisy breathing, chest pain or a very fast or irregular heartbeat, confusion, fainting or fits. Painful spasms of the hands or face with tingling after neck surgery need same-day medical advice.

Mild tingling or cramps with a clear cause are handled by the GP with blood tests. Symptomatic or very low calcium means hospital admission. Long-term parathyroid problems are overseen by an endocrinology team.

Private endocrinology can offer faster appointments for repeated low calcium of unclear cause. Bring a list of medicines, details of any neck surgery and recent blood results. Parathyroid UK is a UK charity for people with parathyroid conditions, as the NHS notes.