The incubation period is usually 7 days but can vary from one day to several months (1,2).
- the incubation period is usually long when the injury site is distant from the central nervous system
- the highest fatality is seen in patients with shortest incubation period (1)
Initially the muscle spasm develops at the site of inoculation (local) and then involves the facial muscles and the muscles of the neck and spine.
Classically, the patient exhibits:
- trismus - lock-jaw due to masseter muscle spasm
- risus sardonicus - characteristic grinning face due to spasm of facial muscles
- opisthotonus - arched body, hyperextended neck due to truncal spasm
- oesophageal spasm - causing dysphagia
- laryngeal spasms (3)
Muscle spasms usually occur spontaneously but touch, visual, auditory or emotional stimuli may act as provocation factors (3)
In severe tetanus, there is profound autonomic instability.
- usually begins a few days after the spasms and persists for 1-2 weeks
- increased sympathetic tone result in vasoconstriction, tachycardia and hypertension
- these ‘autonomic storms’ (associated with raised catecholamine levels) alternate with episodes of sudden hypotension, bradycardia and asystole.
- other autonomic dysfunction include - sweating, salivation, increased bronchial secretions, hyperpyrexia, gastric stasis and ileus (3)
Death results from aspiration, respiratory failure, cardiac failure, or exhaustion.
Poor prognostic signs are:
- short incubation period from the time of injury to the onset of spasms - less than 5 days
- convulsions within 48 hours of the onset of muscle spasm
- occurrence post-partum or post-infection
- occurrence in neonates or elderly
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