Tetanus
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Direct answer
Tetanus is a toxin-mediated neuromuscular disease caused by Clostridium tetani, a spore-forming gram-positive bacillus with a characteristic drumstick appearance, whose toxin tetanospasmin travels retrogradely along peripheral nerves to the central nervous system and blocks the release of inhibitory neurotransmitters glycine and GABA. The result is disinhibition of motor neurons producing muscle spasms classically beginning with trismus (lockjaw), progressing to risus sardonicus, opisthotonus and stimulus-triggered generalised spasms with a clear sensorium. Management combines wound debridement, human tetanus immunoglobulin, metronidazole, spasm control with benzodiazepines or magnesium, and airway protection in a quiet environment, followed by active immunisation because natural infection confers no immunity.
What you must remember
- The organism grows anaerobically in devitalised wounds (rust itself is irrelevant; spores are ubiquitous in soil and faeces), and tetanospasmin blocks inhibitory neurotransmitter release at Renshaw cells — excitation without invasion, with normal cerebrospinal fluid.
- Incubation period is commonly 3–21 days; a shorter incubation, short onset interval and cephalic forms indicate worse prognosis.
- Clinical sequence: trismus is usually the first sign, then neck stiffness, dysphagia, risus sardonicus, opisthotonus, and reflex spasms triggered by noise, light or touch; fever is absent or mild, and consciousness is preserved.
- Treatment of the wound: thorough debridement and cleaning; human tetanus immunoglobulin is given in a dose commonly quoted as 3000–6000 IU intramuscularly, part infiltrated around the wound.
- Metronidazole is the preferred antibiotic; penicillin is now avoided by many units as it is a GABA antagonist and may aggravate spasms.
- Spasms are controlled with diazepam or midazolam infusions, magnesium sulphate infusion, and if severe, paralysis with ventilation via tracheostomy; autonomic instability requires intensive care.
- Every patient still needs a full course of tetanus toxoid, since the tiny amount of toxin causing disease is not immunogenic.
Common confusion
Tetanus is confused with other causes of trismus and with strychnine poisoning. In tetanus the spasms persist between stimuli and the mind is clear, whereas strychnine produces intermittent convulsions with relaxation between them. The other exam-tested contrast is tetanus versus tetany: tetany from hypocalcaemia gives carpopedal spasm with Chvostek and Trousseau signs, not trismus with opisthotonus. Finally, remember neonatal tetanus from unhygienic umbilical practices remains reported in parts of India — it is preventable by maternal immunisation.
Exam-focused takeaway
Questions cluster around mechanism (disinhibition by blocking glycine and GABA), first clinical sign (trismus), drug of choice (metronidazole with immunoglobulin and debridement) and prophylaxis schedules for different wound categories. A classic stem describes a farmer with a puncture wound days earlier presenting with jaw stiffness and a sarcastic smile on attempted mouth opening. Also revise the immunisation table — clean minor wounds in an immunised person need no immunoglobulin, while tetanus-prone wounds in unimmunised patients need both immunoglobulin and toxoid.
Frequently asked questions
Why does the tetanus patient remain conscious?
Tetanospasmin blocks inhibitory interneurons rather than the cortex, so painful spasms occur in a fully aware patient, which is why sedation and a quiet, darkened room matter.
How is tetanus differentiated from meningitis?
Both can cause neck stiffness, but tetanus has a clear sensorium, no headache or photophobia pattern, normal cerebrospinal fluid and stimulus-triggered spasms with trismus.
What is the role of magnesium sulphate in tetanus?
An infusion controls spasms and autonomic cardiovascular instability, reducing the need for sedation and ventilation in many patients per controlled experience.
Why is metronidazole preferred over penicillin?
Metronidazole is equally effective against the organism without penicillin's GABA-antagonistic activity, which can theoretically worsen muscle spasms.
Does recovering from tetanus give immunity?
No; the toxin quantity causing disease is too small to be immunogenic, so active vaccination with toxoid must be completed during recovery.