Tetany

Tetany refers to a condition in which the nerves innervating a particular muscle become overstimulated and cause involuntary contractions of muscles called as spasms. Tetany is also referred to as tetanic seizures.

Table of Content:

Manifestations:

  • 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

  1. Hypocalcemia- This condition refers to a below-normal level of calcium in plasma. Note- the normal concentration of calcium ions in a healthy adult is about 8-10.5 mg/dl in serum. Low free calcium levels in the plasma increase 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 increase the calcium levels in the plasma. Now, this can be achieved by various methods.

Firstly, it takes out or mobilizes calcium from bone to plasma.

Secondly, it can increase absorption of calcium present in the food through the intestine to increase calcium in the plasma.

Lastly, it can increase the plasma calcium levels through increased resorption of calcium from renal tubules thereby increasing calcium levels in blood plasma and reducing it in 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 due to 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– An infection of clostridium tetany releases a neurotoxin 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 manifestation 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 in case of C.infection. For the prevention of tetanus, DPT (Diptheria, Pertussis, Tetanus) vaccination in childhood is advised.

Questions and Answers:

Q1. Do tetany and tetanus mean the same thing? What is the difference between tetany and tetanus?

One should not get confused between these two terms. Here are some differences between the two.

Tetany Tetanus
Tetany is basically a symptom (muscle twitches, spasms and seizures) Tetanus is an infectious and non-communicable disease.
May be caused due to various conditions such as hypocalcemia, Hypomagnesemia, hypokalaemia and tetanus Caused by Clostridium tetani. In this disease, the bacterium releases a neurotoxin which affects the central nervous system
Tetany may be associated with various conditions and diseases like tetanus, hypoparathyroidism etc. This disease can cause various manifestations or symptoms out of which tetany is one of them. Other manifestations include stiffness in the jaw muscles (lockjaw disease), fever, rapid heart rate (tachycardia)

Q2.Calcium ion concentration ion blood affects muscles contractions. Does it lead to tetany in certain cases? How will you correlate fluctuations in calcium levels with tetany? (NCERT)

Calcium ion concentration helps the muscle to contract in the following way :

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

(b)The calcium so released goes and binds to the TpC subunit of troponin protein.

(c)The active site on actin is exposed as Ca2+ binds with troponin

(d)The myosin head forms cross-bridge with actin and contraction takes place.

If the levels of calcium fall 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.

 

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