Tetany

Tetany is a state of motor hyperactivity characterised by spasms, cramps, or twitching of the skeletal muscles. The involuntary contractions experienced in tetany are due to the increased frequency of action potentials.

What is Tetany?

Tetany is a symptom characterised by muscle cramps, spasms, or tremors. The uncontrollable contractions result in sustained or intermittent spasms of skeletal muscles. Tetany can occur in any muscle of the body (including the face, fingers, etc.), and the associated muscle cramps are long-lasting and painful.

Muscle cramps caused by tetanospasmin (neurotoxin from Clostridium tetani) during the disease tetanus are not classified as tetany; they are caused due to inhibition of glycine-mediated and GABA-ergic neurotransmissions in the muscles.

Causes of Tetany

The usual cause of tetany is hypocalcemia (low calcium levels in the bloodstream).

Hypocalcemia increases the permeability of the neuronal membrane to sodium ions (Na⁺), resulting in a progressive depolarisation, which increases the frequency of action potentials. Hypocalcemia severe enough (usually <4.5 mg/dL ionised calcium, or total calcium <7.0 mg/dL) can spontaneously trigger action potentials and tetany.
An excess of phosphate can also trigger muscle spasm if it results in a high phosphate-to-calcium ratio.
Hypoparathyroidism results in a decrease of PTH (Parathyroid Hormone) and leads to hypocalcemia, which can trigger tetany.
Magnesium deficiency impairs PTH secretion and action which leads to hypocalcemia-induced tetany.
Severe hypokalemia (low potassium levels) may cause muscle weakness and arrhythmias, but not classic tetany.
Conditions like chronic kidney disease, pancreatitis, malabsorption syndromes, or vitamin D deficiency can cause electrolyte imbalance leading to tetany.
Hyperventilation might result in hypocapnia (low carbon dioxide), which might cause alkalosis. During alkalosis, Ca⁺² ions bind more readily to the albumin protein in blood, reducing the fraction of ionised calcium. The resulting hypocalcemia can trigger tetany.

Symptoms of Tetany

Paresthesia (tingling sensations in the distal extremities), twitching and shaking of fingers and toes, muscle numbness, and muscle ache. Painful contraction of hand and foot muscles that causes flexion at the wrist and ankle.
Laryngospasm (spasms in the larynx)
Tachypnoea (rapid breathing) and convulsion episodes
Abdominal pain or cramping, chronic persistent diarrhoea, and vomiting
Hypocalcemia can cause ECG changes (prolonged QT interval), arrhythmias, or heart failure in severe cases.
Lethargy and malaise

Frequently Asked Questions (FAQs)

Q1. How would you treat tetany?

A. Severe tetany is treated with intravenous calcium; mild hypocalcemia is treated with oral supplements of calcium and vitamin D. In alkalosis-induced tetany, treatment focuses on correcting underlying cause and administering calcium. To maintain optimum magnesium (Mg²⁺) levels, magnesium tablets are required.

Q2. How can tetany be diagnosed clinically?

A. Some clinical signs like –

Tapping the facial nerve causes twitching of facial muscles (Chvostek’s sign)
Inflating a BP cuff on the arm induces carpopedal spasm (Trousseau’s sign).

Blood tests also confirm low ionised calcium, magnesium, or abnormal PTH levels.

Q3. What is the difference between tetany and tetanus?

A. Tetany is caused by electrolyte imbalance (mainly hypocalcemia) leading to neuromuscular excitability, whereas tetanus is caused by infection with Clostridium tetani producing tetanospasmin toxin that blocks inhibitory neurotransmitters. Although both cause muscle spasms, their mechanisms and treatments are different.