tetanus

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Tetanus 



The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, rod-shaped, obligate anaerobic bacterium Clostridium tetani.


Infection generally occurs through wound contamination and often involves a cut or deep puncture wound. As the infection progresses, muscle spasms develop in the jaw (thus the name lockjaw) and elsewhere in the body.
Infection can be prevented by proper immunization or post-exposure prophylaxis.


Signs and symptoms

Tetanus often begins with mild spasms in the jaw muscles—also known as lockjaw
The spasms can also affect the chest, neck, back, abdominal muscles, and buttocks. 
Back muscle spasms often cause arching, called opisthotonos. Sometimes the spasms affect muscles that help with breathing, which can lead to breathing problems.

These episodes can cause fractures and muscle tears. Other symptoms include drooling, excessive sweating, fever, hand or foot spasms, irritability, swallowing difficulty, and uncontrolled urination or defecation.

Incubation period

The incubation period of tetanus may be up to several months, but is usually about eight days.

four different forms of tetanus have been described.

Generalized tetanus

This is the most common type of tetanus, representing about 80% of cases. The generalized form usually presents with a descending pattern. The first sign is trismus, or lockjaw, and the facial spasms called risus sardonicus, followed by stiffness of the neck, difficulty in swallowing, and rigidity of pectoral and calf muscles. 
Other symptoms include elevated temperature, sweating, elevated blood pressure, and episodic rapid heart rate. 

Spasms may occur frequently and last for several minutes with the body shaped into a characteristic form called opisthotonos. Spasms continue for up to four weeks, and complete recovery may take months.
Sympathetic overactivity (SOA) is common in severe tetanus and manifests as labile hypertension, tachycardia, dysrhythmia, peripheral vasculature constriction, profuse sweating, fever, increased carbon dioxide output, increased catecholamine excretion and late development of hypotension. Death can occur within four days.

Neonatal tetanus

This is a form of generalized tetanus that occurs in newborns. 


Local tetanus

This is an uncommon form of the disease, in which patients have persistent contraction of muscles in the same anatomic area as the injury. The contractions may persist for many weeks before gradually subsiding. It may precede the onset of generalized tetanus.


Cephalic tetanus

This is a rare form of the disease, occasionally occurring with otitis media (ear infections) in which C. tetani is present in the flora of the middle ear, or following injuries to the head.
There is involvement of the cranial nerves, especially in the facial area.


Cause

Tetanus is caused by the tetanus bacterium Clostridium tetani. Tetanus is often associated with rust, especially rusty nails. Objects that accumulate rust are often found outdoors, or in places that harbour anaerobic bacteria, but the rust itself does not cause tetanus nor does it contain more C. tetani bacteria. The rough surface of rusty metal merely provides a prime habitat for C. tetani endospores to reside in, and the nail affords a means to puncture skin and deliver endospores deep within the body at the site of the wound.

Pathophysiology

Tetanus affects skeletal muscle, a type of striated muscle used in voluntary movement. The other type of striated muscle, cardiac, or heart muscle, cannot be tetanized because of its intrinsic electrical properties.

The tetanus toxin initially binds to peripheral nerve terminals. It is transported within the axon and across synaptic junctions until it reaches the central nervous system. There it becomes rapidly fixed to gangliosides at the presynaptic inhibitory motor nerve endings, and is taken up into the axon by endocytosis. The effect of the toxin is to block the release of inhibitory neurotransmitters glycine and gamma-Aminobutyric acid (GABA) across the synaptic cleft, which is required to check the nervous impulse. If nervous impulses cannot be checked by normal inhibitory mechanisms, the generalized muscular spasms characteristic of tetanus are produced. The toxin appears to act by selective cleavage of a proteincomponent of synaptic vesicles, synaptobrevin II, and this prevents the release of neurotransmitters by the cells.


Diagnosis


There are currently no blood tests for diagnosing tetanus. The diagnosis is based on the presentation of tetanus symptoms and does not depend upon isolation of the bacterium, which is recovered from the wound in only 30% of cases and can be isolated from patients without tetanus. Laboratory identification of C. tetani can be demonstrated only by production of tetanospasmin in mice.

The "spatula test" is a clinical test for tetanus that involves touching the posterior pharyngeal wall with a sterile, soft-tipped instrument and observing the effect. A positive test result is the involuntary contraction of the jaw (biting down on the "spatula") and a negative test result would normally be a gag reflex attempting to expel the foreign object. 


Treatment

Mild cases of tetanus can be treated with:
tetanus immunoglobulin IV or IM
metronidazole IV for 10 days
diazepam

Severe cases will require admission to intensive care. In addition to the measures listed above for mild tetanus:
Human tetanus immunoglobulin injected intrathecally (increases clinical improvement from 4% to 35%)
Tracheotomy and mechanical ventilation for 3 to 4 weeks. Tracheostomy is recommended for securing the airway, because the presence of an endotracheal tube is a stimulus for spasm
Magnesium, as an intravenous (IV) infusion, to prevent muscle spasm
Diazepam as a continuous IV infusion

The autonomic effects of tetanus can be difficult to manage (alternating hyper- and hypotension hyperpyrexia/hypothermia) and may require IV labetalol, magnesium, clonidine, or nifedipine

Drugs such as diazepam or other muscle relaxants can be given to control the muscle spasms. In extreme cases it may be necessary to paralyze the patient with curare-like drugs and use a mechanical ventilator.

In order to survive a tetanus infection, the maintenance of an airway and proper nutrition are required. An intake of 3,500 to 4,000 calories, and at least 150 g of protein per day, is often given in liquid form through a tube directly into the stomach (percutaneous endoscopic gastrostomy), or through a drip into a vein (parenteral nutrition). This high-caloric diet maintenance is required because of the increased metabolic strain brought on by the increased muscle activity. Full recovery takes 4 to 6 weeks because the body must regenerate destroyed nerve axon terminals.





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