Tetanus

Overview

Microbiology & Pathophysiology

• C. tetani is a motile, non-encapsulated, obligate anaerobic, gram-positive spore-forming rod
• Spores are ubiquitous in soil, animal feces, and contaminated surfaces — they survive for years
• It is non-invasive; disease requires tissue conditions that reduce oxygen tension (devitalized tissue, foreign bodies, infection) to allow spore germination into the toxin-producing vegetative form

1. Tetanolysin — facilitates bacterial growth
2. Tetanospasmin — the powerful neurotoxin responsible for all clinical manifestations

• Produced at the wound site → binds motor nerve endings → travels by retrograde axonal transport to the CNS
• Does not cross the blood-brain barrier directly
• In the CNS, it blocks presynaptic release of inhibitory neurotransmitters — primarily glycine and GABA — at inhibitory interneurons afferent to alpha motor neurons
• Result: loss of inhibitory control → sustained excitatory discharge → characteristic muscle spasms
• May also affect preganglionic sympathetic neurons and parasympathetic centers → autonomic dysfunction
• Binding is irreversible; recovery requires regrowth of new axonal terminals

Epidemiology

• Worldwide: ~100,000 cases/year; mortality 35–40%
• In the US: >95% decline since 1947 due to vaccination; ~197 cases reported 2009–2015 with 16 deaths
• Highest incidence: adults >65 years (immunity waning); up to 50% of US cases in injection drug users
• Case fatality rate: ~8–18% overall; approaches 50% in patients >70 years
• Neonatal tetanus: ~34,000 deaths/year globally (WHO) from unsterile umbilical stump practices
• Risk factors: inadequate primary immunization, waning immunity (only 31% of Americans >70 have adequate immunity), injection drug use, diabetes, deep puncture wounds

Portals of Entry

• Puncture wounds, lacerations, abrasions (most common, >70% of cases)
• Chronic skin ulcers, abscesses
• Otitis media, dental procedures
• Childbirth (umbilical stump in neonates)
• Surgical procedures (intestinal, abortion)
• No apparent wound in ~10–30% of patients

Clinical Forms

1. Generalized Tetanus (~80% of cases)

• Most common and most severe form
• Trismus ("lockjaw") — masseter spasm — classic presenting symptom (50–75% of patients)
• Risus sardonicus — characteristic sardonic smile from facial muscle involvement
• Progression: facial muscles → neck → trunk → extremities (descending pattern)
• Reflex spasms and tonic contractions cause: dysphagia, opisthotonos (decorticate-like posturing), clenched fists, extended lower extremities
• Spasms can cause vertebral/long bone fractures and tendon rupture
• Laryngospasm and respiratory muscle spasm → ventilatory failure → death
• Autonomic dysfunction (typically 2nd week): tachycardia, labile hypertension, hyperpyrexia, cardiac dysrhythmias, profuse sweating, elevated catecholamines — the major cause of death in patients surviving the acute phase
• Mental status is normal throughout (key diagnostic point) unless respiratory compromise develops
• Illness progresses over ~2 weeks; recovery takes ≥4 weeks

2. Localized Tetanus

• Persistent spasm confined to muscles near the wound site
• Usually resolves over weeks–months; may progress to generalized form
• ~1% fatality

3. Cephalic Tetanus

• Follows head/neck injury or otitis media
• Cranial nerve dysfunction — most commonly CN VII
• Poor prognosis; may precede generalized form

4. Neonatal Tetanus

• A form of generalized tetanus in infants born to inadequately immunized mothers
• Infection through umbilical stump
• Presents in 2nd week of life: weakness, irritability, inability to suck
• High mortality

Diagnosis

• Wound cultures: positive in only 1/3 of cases; not reliable
• Serum calcium: rule out hypocalcemia
• CT brain: exclude intracranial disease
• LP: to exclude meningitis (especially in neonates)
• EMG: may help in cephalic or localized tetanus

• Touch the posterior pharynx with a tongue blade
• Positive (tetanus): reflex masseter spasm → patient bites the spatula
• Negative (no tetanus): gag reflex, expels blade
• Sensitivity 94%, specificity 100%

Differential Diagnosis

Management

1. Supportive Care — Control Muscle Spasms

• Minimize sensory stimuli: quiet, darkened room (light/noise trigger spasms)
• Benzodiazepines (diazepam, midazolam): first-line for spasm control — enhance GABA activity
• Intrathecal baclofen: GABA-B agonist; effective for refractory spasms
• Neuromuscular blocking agents (vecuronium, pancuronium) + mechanical ventilation: for severe, uncontrolled spasms
• Magnesium sulfate: attenuates autonomic instability (reduces catecholamine release)
• Autonomic dysfunction: morphine, labetalol, clonidine, or magnesium to blunt swings
• Tracheostomy often required for prolonged mechanical ventilation

2. Eliminate Unbound Toxin

• Human Tetanus Immunoglobulin (HTIG) — neutralizes circulating tetanospasmin before it enters neurons
  • 500 units IM (some sources recommend 3,000–6,000 units)
  • Infiltrate around wound if possible
  • Does not reverse toxin already bound to nerve tissue

3. Prevent Further Toxin Production

• Wound debridement — remove devitalized tissue and foreign bodies
• Metronidazole (drug of choice): 500 mg IV/PO q6h × 7–10 days (kills vegetative C. tetani)
  • Pediatric dosing varies by weight/age
• Penicillin G: alternative (historically used but a GABA antagonist — metronidazole preferred)

4. Active Immunization

• Tetanus toxoid must be given — clinical tetanus does not confer immunity (toxin levels too low to stimulate immune response)
• Administer at a different site from HTIG

Prophylaxis (Wound Management)

• HTIG dose: 250 units IM (separate injection site from toxoid)
• Children <7 years: DTaP (or DT if pertussis contraindicated)
• ≥7 years and adults: Tdap preferred (one lifetime dose); subsequent boosters with Td every 10 years

• 3-dose primary series → immunity in nearly 100%
• Immunity wanes 5–10 years after series
• Tdap single booster replaces one Td dose for adolescents/adults
• Not contraindicated in pregnancy

Complications

• Respiratory failure (laryngospasm, respiratory muscle spasm)
• Aspiration pneumonia (50–70% of autopsy cases)
• Rhabdomyolysis
• Long-bone and vertebral fractures (from violent contractions)
• Cardiac dysrhythmias
• Death (primarily from autonomic instability in survivors of the acute phase)

Prognosis

• Shorter incubation period → worse prognosis
• Age >70: case fatality ~50%
• Recovery depends on regrowth of axonal nerve terminals (weeks to months)
• Fully vaccinated patients: no reported deaths