19. Tetanus

1. Definition

• Tetanus → acute toxin-mediated disease with muscle rigidity and painful spasms, caused by Clostridium tetani
• Not transmitted from person to person
• No lasting immunity after the disease → vaccinate after recovery

2. Epidemiology

• Rare where vaccination is routine; neonatal tetanus in low-income countries
• Mortality → 10–50% (higher in neonates and the elderly)

3. Aetiology and risk factors

• Clostridium tetani → Gram-positive, anaerobic, spore-forming rod; drumstick appearance
• Spores → soil, dust, animal faeces; very resistant to heat and disinfectants
• Tetanus-prone wounds:
  • Deep puncture wounds → nails, thorns, splinters
  • Soil or manure contamination
  • Devitalised tissue, crush injury, foreign bodies
  • Burns, frostbite
  • Wounds treated > 6 h after injury
  • Open fractures, gunshot wounds
  • Injecting drug use, umbilical stump, septic abortion
• Unvaccinated or incompletely vaccinated patients

4. Pathogenesis

1. Spores enter the wound
2. Anaerobic conditions (dead tissue, foreign body) → spores germinate into vegetative bacteria
3. Bacteria produce tetanospasmin (neurotoxin) and tetanolysin
4. Toxin enters motor nerve endings → retrograde axonal transport to the spinal cord and brainstem
5. Toxin blocks release of inhibitory neurotransmitters (GABA and glycine) from inhibitory interneurones
6. Uninhibited motor neurones → rigidity and spasms
7. Sympathetic overactivity → autonomic instability
8. Binding of toxin to neurones → irreversible; recovery needs new nerve terminals (4–6 weeks)
9. Incubation period → 3–21 days (average 7–10)
10. Short incubation (< 7 days) and short onset period (< 48 h) → severe disease, poor prognosis

5. Classification

1. Generalised → most common (80%); descending spread
2. Localised → rigidity near the wound; may become generalised
3. Cephalic → head wounds, otitis; cranial nerve palsies (facial nerve)
4. Neonatal → infected umbilical stump; inability to suck

6. Clinical picture

Prodrome

• Restlessness, irritability, headache
• Pulling pain and twitching around the wound

Rigidity (descending order)

1. Trismus (lockjaw) → masseter spasm; first sign in most patients
2. Risus sardonicus → sardonic smile from facial muscle spasm
3. Neck stiffness, dysphagia
4. Rigid abdominal wall (board-like)
5. Opisthotonus → arched back from paravertebral muscle spasm
6. Rigid limbs → arms flexed, legs extended

Spasms

• Painful generalised tonic spasms, triggered by noise, light, touch
• Patient fully conscious during spasms
• Laryngeal and diaphragmatic spasm → asphyxia
• Spasms may cause fractures (vertebral), muscle rupture

Autonomic dysfunction

• Labile hypertension and hypotension, tachycardia, arrhythmias
• Sweating, hyperpyrexia
• Cardiac arrest

7. Diagnosis

• Clinical diagnosis → no specific laboratory test
• Wound culture → positive in only 30%; negative does not exclude
• Spatula test → touching the posterior pharynx causes reflex masseter spasm (bites the spatula)
• Creatine kinase may be raised

8. Differential diagnosis

• Dental abscess, peritonsillar abscess → trismus
• Strychnine poisoning
• Dystonic reaction to drugs (metoclopramide, haloperidol)
• Meningitis, encephalitis
• Hypocalcaemic tetany
• Rabies
• Neuroleptic malignant syndrome

9. Treatment

Wound

• Surgical debridement of the wound → remove the source of toxin
• Leave the wound open

Neutralise unbound toxin

• Human tetanus immunoglobulin (HTIG) → 3000–6000 IU intramuscularly (some use 500 IU)
• Antitoxin binds only circulating toxin, not toxin already in neurones

Kill bacteria

• Metronidazole → drug of choice; 500 mg intravenously every 8 h for 7–10 days
• Penicillin → alternative

Control spasms

• Quiet, dark room; minimal handling
• Benzodiazepines → diazepam, midazolam
• Magnesium sulphate → spasms and autonomic instability
• Neuromuscular blockade with ventilation → severe cases
• Baclofen (intrathecal)

Supportive care in the intensive care unit

• Early tracheostomy → airway protection, prolonged ventilation
• Autonomic control → magnesium, labetalol, morphine
• Nutrition via nasogastric tube or gastrostomy
• Fluids, thromboprophylaxis, prevention of pressure ulcers
• Active immunisation with tetanus toxoid at a different site → disease does not give immunity

10. Prevention

Active immunisation

• Tetanus toxoid → primary course in childhood, boosters
• Full immunity → 5 doses in life

Prophylaxis after injury

• Wound care and debridement in every case
• Clean minor wound:
  • Vaccination complete → no vaccine needed (booster if > 10 years since last dose)
  • Incomplete or unknown → toxoid
• Tetanus-prone wound:
  • Vaccination complete, last dose < 5 years → nothing more
  • Vaccination complete, last dose > 5 years → toxoid booster
  • Incomplete or unknown → toxoid + human tetanus immunoglobulin 250 IU (500 IU if > 24 h or heavy contamination)
• Toxoid and immunoglobulin → different sites, different syringes

11. Complications

• Asphyxia, aspiration pneumonia
• Autonomic crises, cardiac arrest
• Vertebral fractures
• Rhabdomyolysis, renal failure
• Complications of prolonged ventilation