Miscellaneous infective or post-infective CNS disorders
Tetanus is a toxin mediated condition causing muscle spasms following a wound infection.
Clostridium tetani (the causative organism), an anaerobic spore forming bacillus, originates from the faeces of domestic animals. It is found widely in the soil.
The bacteria enter the body at the site of a wound and if there is an anaerobic environment (e.g. if there is a foreign material present in the wound) they replicate and produce a neurotoxin, tetanospasmin. This toxin travels along the sheaths of peripheral nerves to the CNS and acts by blocking the release of inhibitory mediators in the spinal motor synapses. The result is an overactivity of both the motor system and the sympathetic nervous system, causing spasms and autonomic dysfunction.
The incubation period can be days to weeks and the wound may be so slight as to be unnoticed.
· Generalised tetanus is the most common presentation, with lockjaw (trismus), caused by masseter spasm. The facial muscles may contort to cause a typical expression (risus sardonicus). Any sensory stimulation such as noise results in generalised muscle spasms including arching of the back (opisthotonos). Spasms of the larynx can impede respiration, and autonomic dysfunction causes arrhythmias, sweating and a labile blood pressure.
· Localised tetanus can occur around the contaminated wound, full recovery is usual.
· Cephalic tetanus is uncommon but invariably fatal. It occurs when C. tetani is inoculated from the middle ear.
The diagnosis is essentially clinical, bacteria are rarely isolated.
Muscle spasms may lead to injury, in severe cases respiratory failure, cardiac arrest or aspiration leading to death.
Following contaminated injury patients require with early wound debridement and the administration of human tetanus immune globulin (passive immunisation) if their immunisation status is unknown or they have not had a booster in the last 5 years.
· A booster dose with tetanus toxoid (which is an inactivated toxin which induces active immunisation), or course of three injections, should additionally be given, as the protection from antitetanus immune globulin only lasts 2 weeks. Antibiotics may also be indicated.
Active tetanus: Patients should be nursed in a quiet, dark area to reduce spasms. Surgical wound debridement should be performed where indicated and intravenous penicillin and high doses of human tetanus immune globulin should be given i.m. (some around the wound). However, the immunoglobulin can only neutralise circulating toxin, it has no affect on bound toxin.
Large doses of diazepam may be needed to reduce spasms and cardiovascular instability is controlled with β blockers. Tracheostomy and ventilatory support may be necessary for severe laryngeal spasm.
Children are routinely vaccinated against tetanus from age 2 months.