Tetany

What tetany is

Nerves and muscles need the right levels of calcium and magnesium to stay stable. Calcium in the fluid around nerve cells helps keep sodium channels closed. When ionized (free, active) calcium falls, nerves fire spontaneously and repeatedly, producing tingling and muscle contractions that the person cannot control.

Tetany can be:

• Overt: obvious spasms and tingling.
• Latent: no symptoms at rest, but signs can be brought out by tests or by overbreathing.

Tetany vs tetanus

These are easy to confuse:

Symptoms

Early or mild

• tingling (paresthesia) around the mouth, lips and tongue
• pins and needles in the fingers and toes
• muscle cramps, twitching and stiffness
• fatigue, irritability, anxiety

Typical tetany

• Carpopedal spasm: the wrist and knuckle joints bend while the fingers straighten and the thumb folds in (a "claw" or "obstetrician's hand"); the feet and toes point downward
• painful cramps in the legs, back or face

Severe

• laryngospasm: spasm of the vocal cords causing stridor and difficulty breathing
• bronchospasm: wheezing
• seizures
• heart rhythm problems, a prolonged QT interval on ECG, and in long-standing low calcium, heart failure

Signs doctors look for

• Chvostek sign: tapping the facial nerve in front of the ear causes twitching of the upper lip or face. It is also positive in some healthy people, so it is not reliable alone.
• Trousseau sign: inflating a blood pressure cuff above systolic pressure on the upper arm for 3 minutes triggers carpopedal spasm. It is more specific for low calcium.

Causes

Low calcium (hypocalcemia)

Hypocalcemia is the commonest cause of tetany. Causes include:

• Hypoparathyroidism: most often after thyroid or parathyroid surgery, when the parathyroid glands that control calcium are removed, bruised or lose their blood supply. Usually temporary, sometimes permanent.
• "Hungry bone" syndrome after parathyroid surgery for overactive glands
• Vitamin D deficiency from little sun, malabsorption or kidney disease
• Chronic kidney disease
• Acute pancreatitis
• Massive blood transfusion (the citrate preservative binds calcium)
• Medicines: bisphosphonates, denosumab, some anti-seizure drugs, foscarnet
• Genetic conditions such as DiGeorge syndrome

Low magnesium

Hypomagnesemia causes tetany directly and also lowers calcium by blocking parathyroid hormone release and action. Causes include alcohol use disorder, diarrhea, long-term proton pump inhibitor use, diuretics and poorly controlled diabetes. Low calcium will not correct until magnesium is replaced.

Alkalosis

When the blood becomes too alkaline, more calcium binds to proteins, so free calcium drops even if total calcium is normal.

• Hyperventilation, often with panic attacks or anxiety
• Prolonged vomiting or excessive antacid use

Other causes

• low potassium combined with other imbalances
• high phosphate levels, as in kidney failure, tumor lysis syndrome or phosphate enemas

How tetany is diagnosed

1. History and exam, including recent neck surgery, medicines, alcohol use, diet and sun exposure, plus the Chvostek and Trousseau signs.
2. Blood tests: calcium (corrected for albumin, or ionized calcium), magnesium, phosphate, potassium, kidney function, parathyroid hormone (PTH) and vitamin D.
3. Blood gas if alkalosis is suspected.
4. ECG to check for a prolonged QT interval or arrhythmia.

Treatment

Emergency treatment

Severe tetany, laryngospasm, seizures or ECG changes need hospital care:

• Intravenous calcium gluconate, given slowly with heart monitoring
• Intravenous magnesium if magnesium is low
• airway support for laryngospasm

Ongoing treatment

• Oral calcium supplements
• Active vitamin D (calcitriol) for hypoparathyroidism, which helps the gut absorb calcium
• Vitamin D3 for deficiency
• Magnesium supplements and stopping medicines that waste magnesium, where possible
• Parathyroid hormone replacement (such as palopegteriparatide) for some adults with chronic hypoparathyroidism
• Treating the cause, such as kidney disease or malabsorption

Blood calcium is monitored closely, because over-treatment can cause high calcium and kidney stones.

Hyperventilation-related tetany

Slow, controlled breathing (breathing out longer than you breathe in) restores carbon dioxide levels and usually relieves symptoms within minutes. Breathing into a paper bag is no longer recommended, as it can lower oxygen levels dangerously in someone who has an undiagnosed heart or lung problem. Treatment for the underlying anxiety or panic disorder prevents recurrence.

Outlook

Tetany usually resolves quickly once calcium, magnesium or breathing is corrected. Temporary hypoparathyroidism after thyroid surgery typically recovers within weeks to months. People with permanent hypoparathyroidism need lifelong treatment and monitoring but can live normally.

Frequently asked questions

What is the most common cause of tetany?

Low blood calcium (hypocalcemia) is the most common cause, often due to damage to the parathyroid glands during thyroid surgery or vitamin D deficiency. Low magnesium and hyperventilation are other frequent causes.

What does tetany feel like?

It usually starts with tingling around the lips and in the fingertips, followed by cramping or stiffening of the hands and feet. The fingers may straighten while the wrist bends. Severe tetany can cause throat tightness, difficulty breathing and seizures.

What is the difference between tetany and tetanus?

Tetany is muscle spasm caused by low calcium, low magnesium or alkalosis. Tetanus is a serious bacterial infection that causes lockjaw and severe body-wide spasms, prevented by vaccination. The names sound similar, but the causes and treatments are completely different.

Can hyperventilation cause tetany?

Yes. Rapid breathing blows off carbon dioxide, making the blood more alkaline. This lowers free calcium, causing tingling and hand spasms. Slow, controlled breathing usually reverses it within minutes. Repeated episodes deserve a medical check for other causes.

How is tetany treated?

Severe tetany is treated in hospital with intravenous calcium and, if needed, magnesium. Milder cases are treated with oral calcium, vitamin D or active vitamin D, and magnesium supplements, while the underlying cause is corrected.