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TETANUS - Comprehensive Exam Answer

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1. DEFINITION

• Mortality: ~8% in the US, 35-40% globally, approaching 50% in patients >70 years
• Notable feature: patient remains conscious (lucid) unless complications arise; fever is usually absent unless secondary infection occurs

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2. ETIOLOGY - THE ORGANISM

1. Tetanolysin - hemolysin; facilitates growth of bacterial population by destroying surrounding tissue
2. Tetanospasmin - the neurotoxin responsible for ALL clinical manifestations; one of the most potent biological toxins known (lethal dose in humans: 2.5 ng/kg)

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3. PATHOGENESIS & MECHANISM OF ACTION

Step-by-Step Pathogenesis:

• Hematogenous spread to peripheral nerve terminals throughout the body
• Retrograde intra-axonal transport (at ~75-250 mm/day) within membrane-bound vesicles, traveling up motor neurons to the spinal cord and brainstem. It does NOT cross the blood-brain barrier directly - retrograde transport is the key route to CNS access.

"Tetanospasmin prevents the release of inhibitory neurotransmitters glycine and GABA (γ-aminobutyric acid) from presynaptic nerve terminals of Renshaw cells and other inhibitory interneurons in the spinal cord."

• Tintinalli's Emergency Medicine

• Loss of inhibitory control → uninhibited, sustained motor neuron firing
• Simultaneous contraction of agonist AND antagonist muscles → tetanic spasms
• Loss of inhibition at preganglionic sympathetic neurons → autonomic dysfunction (sympathetic overactivity, high catecholamine levels)

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4. RISK FACTORS / PORTALS OF ENTRY

• Puncture wounds, lacerations, abrasions (most common - ~70% of cases)
• Contaminated wounds with soil/manure
• Chronic skin ulcers, abscesses
• Burn wounds
• Otitis media (cephalic tetanus)
• Injection drug users (50% of US cases)
• Neonates - through unclean umbilical cord care
• Childbirth/abortion (obstetric tetanus)
• Dental procedures
• Patients with diabetes, immunosuppression
• Waning immunity (>65 year age group, lack of booster vaccination)

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5. INCUBATION PERIOD

• Usually 3 to 21 days (mean: 7-8 days), ranging from 4 to 14 days
• Shorter incubation = worse prognosis (toxin reaches CNS faster, meaning the wound is closer to the spinal cord)

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6. CLINICAL TYPES

A. Generalized Tetanus (Most Common - 80-90%)

• Trismus (lockjaw) - initial complaint in ~75% of cases - spasm of masseter muscles; patient often presents to a dentist first
• Risus sardonicus - persistent spasm of facial muscles producing a fixed, grimacing smile (see image below)
• Dysphagia - pharyngeal spasm
• Neck rigidity - opisthoclonus progressing to full opisthotonus
• Opisthotonus - severe arching of the back due to paraspinous muscle spasm (extensor muscles dominate)
• Generalized convulsive spasms - precipitated by any stimulus (noise, light, touch)
• Respiratory failure - laryngeal spasm causing apnea; the most common cause of death
• Autonomic Nervous System Dysfunction (ANSD) - appears in week 2 of severe disease (see below)

B. Localized Tetanus

• Muscle spasms confined to the area near the wound
• Can progress to generalized tetanus
• Mild form; persistent contractions in the affected extremity
• Relatively rare

C. Cephalic Tetanus

• Follows head injuries or middle ear infection (otitis media)
• Involves cranial nerves - most commonly facial nerve palsy
• Short incubation: 1-2 days
• Can involve laryngeal/pharyngeal muscles - aspiration, respiratory failure, airway obstruction
• Often progresses to generalized tetanus

D. Neonatal Tetanus (Tetanus Neonatorum)

• Occurs in neonates of unimmunized mothers through unclean umbilical cord practices
• Presents on days 3-10 of life
• Features: inability to suck, poor feeding, generalized spasms, irritability, opisthotonos
• WHO estimates ~34,000 neonatal deaths/year
• Differential: Hypocalcemia, meningoencephalitis, septicemia

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7. ABLETT CLASSIFICATION OF SEVERITY

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8. AUTONOMIC NERVOUS SYSTEM DYSFUNCTION (ANSD)

• Occurs in week 2 of severe tetanus
• Death due to cardiovascular events becomes the leading risk at this stage
• Features:
  • Labile BP - hypertension alternating with hypotension
  • Labile heart rate - tachycardia alternating with bradycardia
  • Profuse diaphoresis
  • Hyperthermia
  • Gastrointestinal stasis
  • Increased tracheal secretions
  • Rhabdomyolysis
  • Urinary retention
• Cause: tetanospasmin blocks inhibitory input to preganglionic sympathetic neurons, leading to catecholamine surge

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9. DIAGNOSIS

• Wound culture: C. tetani can be isolated in only 30% of cases; a positive culture alone is NOT confirmatory
• Serum anti-tetanus IgG: levels >0.1 IU/mL are considered protective and argue against tetanus; levels below this support the diagnosis
• PCR / recombinase polymerase amplification for tetanus neurotoxin gene - promising but not routinely available
• Spatula test (tongue depressor test): touching the posterior pharynx with a spatula elicits reflex masseter spasm (positive in tetanus) rather than gag reflex - this bedside test has high sensitivity

• ABG - for respiratory status
• Electrolytes, creatinine, LFTs - baseline
• CK - elevated (rhabdomyolysis)
• ECG - cardiac arrhythmias
• Wound swab culture

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10. DIFFERENTIAL DIAGNOSIS

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11. MANAGEMENT

1. Neutralize circulating unbound toxin (antitoxin)
2. Remove source of toxin production (wound care + antibiotics)
3. Control spasms and support vital functions
4. Manage autonomic dysfunction and complications

A. General Supportive Care

• Admit to ICU - quiet, darkened room (minimize sensory stimuli - noise and light trigger spasms)
• Secure airway early in Grade III/IV tetanus - early elective tracheostomy is preferred over orotracheal intubation (which itself can trigger spasm)
• Mechanical ventilation if needed (may require weeks)
• Nasogastric tube for feeding (due to dysphagia)
• DVT prophylaxis, bladder care, pressure sore prevention
• Nutritional support

B. Antitoxin (Passive Immunization)

• Neutralizes only circulating, unbound toxin - does NOT reverse already-bound toxin
• Give EARLY before wound debridement

C. Wound Care

• Identify and debride the wound - remove all necrotic tissue, foreign bodies, pus
• Perform wound care several hours AFTER antitoxin administration
• Failure to debride may cause recurrent/prolonged tetanus

D. Antibiotics

• Metronidazole - DRUG OF CHOICE: 400 mg rectally or 500 mg IV every 6 hours for 7 days
• Penicillin - Alternative (but AVOID if possible - it competitively inhibits GABA receptors, theoretically worsening spasms; one study showed increased mortality)

E. Control of Spasms

F. Management of Autonomic Dysfunction

• Magnesium sulfate - first-line (controls both hypertension AND tachycardia; plasma level 2-4 mmol/L)
• Beta-blockers (labetalol, propranolol, esmolol) - for persistent tachycardia/hypertension (use cautiously - can cause sudden cardiac arrest due to loss of sympathetic compensation)
• Calcium channel blockers - alternative
• Vasopressors (norepinephrine) - when parasympathetic predominance causes hypotension and bradycardia

G. Immunization (Active)

• Since tetanospasmin is poorly immunogenic, surviving tetanus does NOT confer immunity
• All patients must receive a full primary immunization course during or after recovery

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12. VACCINATION SCHEDULE (WHO / CDC Recommendations)

Wound Management Algorithm:

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13. COMPLICATIONS

• Respiratory failure / Aspiration pneumonia - most common cause of death
• Cardiovascular events - autonomic dysfunction (Week 2 peak risk)
• Rhabdomyolysis - from sustained muscle contractions
• Vertebral / long bone fractures from violent spasms
• Pulmonary embolism
• Hospital-acquired infections (VAP, bloodstream infections, UTI) - due to prolonged ICU stay
• Pressure sores, muscle weakness - from immobility and high-dose sedation
• Laryngeal spasm leading to asphyxia - most immediate life-threatening event
• Neonatal sequelae: neurological - cerebral palsy, deafness, learning disabilities

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14. PROGNOSIS

• Recovery usually takes 4-6 weeks (time for new axon terminals to grow)
• Shorter incubation period → worse prognosis
• Shorter period of onset (time from first symptom to first generalized spasm) → worse prognosis
• Scoring systems:
  • Tetanus Severity Score (TSS) - most accurate (sensitivity 66%, specificity 91%)
  • Dakar Score (6 parameters: incubation period, period of onset, portal of entry, spasms, fever, tachycardia)
  • Phillips Score

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15. HIGH-YIELD EXAM POINTS - QUICK SUMMARY

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