What is tetany and how low calcium causes muscle spasms
Tetany refers to a condition during which the nerves innervating a specific muscle becomes overstimulated and causes involuntary contractions of muscles called Spasms.Tetany is also referred to as Tetanic Seizures.
Symptoms of Tetany
Includes spasms of the carpal(wrist) muscles, an extension in interphalangeal joints(joint present between bones of fingers of hands and toes of feet)
Spasms in the larynx(laryngospasm)
Convulsion episodes
Tingling sensation in distal extremities called paresthesias.
Heart dysfunction, vomiting.
Causes of Tetany
Hypocalcemia-This conditions define a below-normal level of calcium in plasma. Note, the basic concentration of calcium ions in a healthy adult is about 8-10.5 mg/dl in serum. Low level of free calcium levels in the plasma increases the depolarization of the neurons thereby increasing neuronal excitability.
What are the Possible ways by which Hypocalcemia can Occur?
(a) Decreased levels of parathormone- Parathormone(PTH) is a hormone released by the parathyroid gland(Glands present behind thyroid gland).PTH functions as maintaining serum calcium levels by exercising its effect on bone, kidneys and intestine. Basically, its main function is to maximize the calcium levels within the plasma. Now, this can be achieved by various methods.
Firstly, calcium is oozed out from bone to plasma.
Secondly, it can increase absorption of calcium present within the food through the intestine to maximize calcium within the plasma.
Lastly, it maximizes the plasma calcium levels through increased resorption of calcium from renal tubules thereby increasing calcium levels in plasma and reducing it within the urine.
Accidental damage to the parathyroid gland, autoimmune disorders, congenital defects can also lead to decreased PTH secretion.
(b) Low vitamin D levels can also cause hypocalcemia as vitamin D helps in absorbing calcium. Low Vitamin D levels can be caused by lack of exposure to sunlight, malnutrition etc.
(c) Other factors include loss of calcium because of the kidney and gastrointestinal diseases.
Low levels of Magnesium- As magnesium is very vital to PTH synthesis.
Alkalosis- An increase in blood pH causes albumin, a blood protein, to bind with free calcium in the plasma. This causes decreased availability of free calcium ions. Severe alkalosis may lead to tetany. Alkalosis may be caused by continuous vomiting(loss of gastric acids), increased intake of alkaline foods etc.
Clostridium Tetany Toxin- A neurotoxin is released by the infection of clostridium Tetany which inhibits the release of neurotransmitters. This can lead to increased muscle tone and muscle spasm. The disease caused so is called tetanus(lockjaw disease)
Hypokalemia-This refers to decreased potassium(K+) concentration in the blood. As we know, potassium is essential for repolarization of nerve cells, a decrease in potassium levels can lead to the various manifestations of tetany.
Treatment of Tetany
Intravenous or oral calcium supplemented with vitamin D
Magnesium administration to maintain optimum Mg2+ levels.
Administration of isotonic fluids, ammonium chloride in case of emergency(in case of alkalosis).
Antibiotics and antitoxin just in case of C.infection. For the prevention of tetanus, DPT(Diphtheria, Pertussis, Tetanus) vaccination in childhood is suggested.
Difference Between Tetany and Tetanus
Role of Calcium Ion in Tetany
Calcium ion concentration plays a vital role in the muscle contraction in the following way :
As an action potential reaches the muscle cells, the sarcoplasmic reticulum releases calcium in the sarcoplasm.
The calcium that is released goes and binds to the TpC subunit of troponin protein.
The active site on actin is exposed as Ca2+ binds with troponin
The myosin head forms a cross-bridge with action and contraction takes place.
If the levels of calcium decrease below normal, it increases the permeability of Na+ ions causing recurring depolarization and contractions. This condition is called tetany. Low calcium levels may be caused due to low parathormone levels.
FAQs on Tetany Explained with Causes Symptoms and Management
1. What is tetany in biology?
Tetany is a condition characterized by involuntary muscle spasms caused mainly by low levels of calcium ions (hypocalcemia) in the blood. It occurs when decreased extracellular calcium increases the excitability of neurons and muscle cells. As a result:
- Nerve cells fire more easily.
- Muscle fibers contract repeatedly without control.
- Symptoms include cramps, twitching, and stiffness.
2. What causes tetany?
Tetany is mainly caused by hypocalcemia, which lowers the threshold for nerve excitation and leads to muscle spasms. Common causes include:
- Hypoparathyroidism (low parathyroid hormone)
- Vitamin D deficiency
- Chronic kidney disease
- Alkalosis (increased blood pH)
- Magnesium deficiency
3. How does low calcium cause tetany?
Low calcium causes tetany by increasing the excitability of nerve cell membranes, leading to spontaneous muscle contractions. Normally, calcium stabilizes voltage-gated sodium channels. When calcium levels fall:
- Sodium channels open more easily.
- Action potentials are triggered rapidly.
- Muscles contract repeatedly without voluntary control.
4. What are the common symptoms of tetany?
The common symptoms of tetany include muscle cramps, spasms, and tingling sensations due to increased neuromuscular excitability. Typical signs are:
- Carpopedal spasm (hand and foot contraction)
- Facial muscle twitching
- Tingling in fingers and lips (paresthesia)
- Muscle stiffness and pain
- In severe cases, laryngeal spasm or seizures
5. What is the difference between tetany and tetanus?
Tetany is caused by low calcium levels, whereas tetanus is caused by infection with the bacterium Clostridium tetani. Key differences include:
- Tetany: Due to hypocalcemia; involves metabolic imbalance.
- Tetanus: Due to bacterial toxin (tetanospasmin); involves infection.
- Tetany improves with calcium correction.
- Tetanus requires antitoxin and antibiotics.
6. What is carpopedal spasm in tetany?
Carpopedal spasm is a sustained contraction of the hands and feet seen in hypocalcemic tetany. It typically presents as:
- Flexion of the wrist and fingers
- Adduction of the thumb
- Extension of the fingers
- Plantar flexion of the foot
7. How is tetany related to parathyroid hormone?
Tetany is closely related to low levels of parathyroid hormone (PTH), which regulates blood calcium concentration. PTH normally:
- Increases calcium release from bones
- Enhances calcium reabsorption in kidneys
- Activates vitamin D for intestinal absorption
8. Can alkalosis cause tetany?
Yes, alkalosis can cause tetany by reducing the amount of free ionized calcium in blood plasma. In alkalosis:
- More calcium binds to plasma proteins like albumin.
- Ionized (active) calcium decreases.
- Neuromuscular excitability increases.
9. How is tetany diagnosed?
Tetany is diagnosed primarily by detecting low serum calcium levels along with characteristic clinical signs. Diagnosis involves:
- Blood tests for calcium, magnesium, and PTH
- Observation of muscle spasms
- Positive Chvostek’s sign (facial twitch on tapping)
- Positive Trousseau’s sign (carpal spasm with BP cuff)
10. How is tetany treated?
Tetany is treated by correcting the underlying cause, especially restoring normal calcium levels. Treatment options include:
- Intravenous calcium in severe cases
- Oral calcium supplements
- Vitamin D supplementation
- Magnesium correction if deficient
- Treating underlying endocrine or kidney disorders
