Tetanus is a serious bacterial infection caused by the bacillus Clostridium tetani. This bacterium produces a powerful neurotoxin known as tetanospasmin that affects the motor nerves, thus interrupting the signals to the muscles, which leads to prolonged rigidity and spasm of various muscles in the body. C. tetani is found universally in the soil, dust and animal feces and the infection is caused by contaminated wounds. There are about 1 million cases of tetanus annually all around the world. The mortality rates from tetanus vary widely depending on the access to healthcare and prevention, with less mortality rates in the developed nations than in developing nations.
What Is The Pathophysiology Of Tetanus Toxin?
C. tetani produces a neurotoxin tetanospasmin that is taken up by the nerve terminals of lower motor neurons (nerve cells responsible for the activation of voluntary muscles). Tetanospasmin toxin is transported to the spinal cord/brainstem, which inhibits the release of GABA and glycine. This inhibition of GABA and glycine leads to increased muscle activity causing rigidity and spasm of the affected muscles.
What Are The Warning Signs Of Tetanus?
Tetanospasmin is associated with hyperactivity of voluntary muscles in the form of rigidity and spasms and these are the warning signs of tetanus. Rigidity refers to continuous muscle contraction of involuntary muscles while spasms are shorter lasting muscle contractions that are mostly evoked by stretching of the muscles. For example, rigidity of the jaw muscles causes lockjaw (trismus) in which there is reduced mouth opening while an attempt to open the mouth can cause a spasm that can lead to clenching of the jaws, it is a warning sign.
Tetanus can either cause generalized (widespread, throughout the body), neonatal (generalized affecting children less than one month of age), local and cephalic (tetanus is localized to the head region). In generalized and neonatal form, tetanus affects the muscles all over the body, which can cause opistotonus (arching of the back muscles due to rigidity of the muscles of neck and back) along with rigidity and spasm of laryngeal and respiratory muscles causing respiratory failure and death. Local and cephalic tetanus can also develop into generalized form.
Depending on the local, cephalic, neonatal or generalized form, tetanus symptoms include trismus (lockjaw), risus sardonicus (spasm of the facial muscles leading to the appearance of a grin on the face), dysphagia (difficulty swallowing), neck stiffness, abdominal rigidity and opistotonus (which is the hyperactivity of the muscles of head, neck and trunk region). The limbs are less frequently affected; however, with full opistotonus the arms and legs are also affected. Lockjaw is the first symptom in most of the cases, but there can be other symptoms including focal paralysis along with lightheadedness.
Tetanospasmin not only affects the motor neurons, but it affects the autonomic nervous system too. When the ANS is involved there can be additional symptoms of tachycardia (increased heart rate), hypertension (increased blood pressure) and diaphoresis (excessive sweating). These symptoms can alternate with bradycardia (reduced heart rate) and hypotension (decreased blood pressure), which is very commonly seen in generalized form of tetanus. These symptoms occur side by side with the increased release of adrenaline and noradrenaline that may lead to myocardial necrosis. Generally, the autonomic symptoms follow (usually a week later) motor symptoms, which is a reflection of the toxin affecting the brainstem. Modern intensive care has reduced tetanus induced respiratory insufficiency and the condition has become treatable. Therefore, most of the deaths that occur nowadays are due to autonomic dysfunction rather than motor dysfunction.
Tetanospasmin can also have effect on sensory nerves. This might lead to altered sensations including pain and allodynia. Allodynia is a perception of pain without the presence of any pain stimulus. In tetanus, most of the altered sensations are present in the head region. It is still unclear whether tetanospasmin affects cognition and mood of a person or not. However, it has also been noted that in neonatal tetanus, tetanospasmin can also cause intellectual disability of the child.
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