Tetany

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.

1. Low levels of Magnesium- As magnesium is very vital to PTH synthesis.

2. 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.

3. 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)

4. 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

1. Intravenous or oral calcium supplemented with vitamin D

2. Magnesium administration to maintain optimum Mg2+ levels.

3. Administration of isotonic fluids, ammonium chloride in case of emergency(in case of alkalosis).

4. 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 :

1. As an action potential reaches the muscle cells, the sarcoplasmic reticulum releases calcium in the sarcoplasm.

2. The calcium that is released goes and binds to the TpC subunit of troponin protein.

3. The active site on actin is exposed as Ca2+ binds with troponin

4. 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.