Question 6

College answer

a)    The differential includes:                                              
•    Strychnine poisoning 
•    Drug induced dystonia 
•    Dental/local infections 
•    Stiff person syndrome 
•    Hypocalcaemia 
•    Malignant Hyperthermia 
•    Stimulant Use 
•    Serotonin syndrome 
•    Seizure disorder 
•    Psychiatric disorders 
 
 
b)    The diagnosis is a clinical one.                                          
•    Appropriate History 
•    Vaccinations status 
•    Tetanus prone wound 
•    Appropriate clinical features 
•    C tetani is cultured from the wound in only 1/3 of cases. There are no specific lab tests to confirm the diagnosis 
 
c)    Passive immunisation.                                               
Human antitetanus immunoglobulin (HIG) has now largely replaced antitetanus serum (ATS) of horse origin as it is less antigenic.it is recommended that HIG  be administered to unimmunised patients or those where their immunisation status is unknown if they present with contaminated wounds 
 
Eradication of the organism.  
•    Wound care. The infected site should the cleaned and all necrotic tissue should be debrided.  
•    Antibiotics .As tetanus spores are destroyed by antibiotics they should be administered.  
•    Recommendations include Metronidazole, penicillin and erythromycin. 

Management of spasms 
•    Intra thecal Baclofen 
•    Magnesium 
•    Diazepam 
•    Muscle relaxants with mechanical ventilation

Management of autonomic dysfunction 
•    Sedation 
•    Alpha and beta blockers 
 

Note: Mention of Human Antitetanus Immunoglobulin was considered essential to score a passing mark 

Discussion

Differentials for whole-body rigidity, opisthotonos and trismus:

• Intracranial catastrophe - increased tone an all 4 limbs should make on think of something happening in the brain stem. The generally increased tone and the spasming arm flexion makes one think of decerebrate posturing. However one does not normally develop a risus sardonicus while having a bilateral brainstem lesion. Most relevantly, one should not be fully alert during an episode of decerebrate posturing.
• Strychnine poisoning - but where does one get a hold of strychnine these days? It is no longer available widely; nowadays most countries which still use it tend to limit its sales. In California, for example it is used as a mole and gopher poison.
• Local temporomandibular disease, causing masseter spasm
• Local oral disease causing masseter spasm
• Epilepsy
• Stiff person syndrome
• Dystonia
• Hypocalcemia
• Serotonin syndrome
• Sympathomimetics

Confirmation of the diagnosis of tetanus:

• Clinically:  the physical findings are quite characteristic. Henderson et al (1998) described a case series where only one case in eleven was misdiagnosed in the ED. "Laboratory results and cultures are of little diagnostic value", the authors concluded.
• The "spatula test" which is where you poke the patient's posterior pharyngeal wall to elicit a masseter spasm; Apte & Karnad (1995) found it had 100% specificity and 94% sensitivity. 
• Wound culture might occasionally grow C.tetani (in 30% of cases)
• Serum antitoxin level: you can't test for the actual tetanospasmin, but you can test for the antitoxin immunoglobulin; levels above 0.1 IU should be protective, so very low levels demonstrate susceptibility and therefore raise the level of clinical suspicion.

Management of tetanus:

• Even though the college sternly warned the exam candidates against talking about generic stuff like airway management, it is actually an important part of the specific management for tetanus because these people usually develop laryngospasm and stridor. 
• Disable the toxin: passive immunisation with tetanospasmin antibodies
  • this will bind circulating toxin only;
  • all the toxin already within the CNS will continue to have its effects, i.e. the symptoms will not resolve
• Destroy the bacterium and its spores: both are sensitive to metronidazole, and thus there is usually a good response. Benzylpenicillin is also added.
• Control the spasms. Usually a neuromuscular junction blocker or benzodiazepine infusion is needed. The college also mention intrathecal baclofen 
• Control the sympathetic nervous system. Usually, an infusion of labetalol, magnesium sulfate or clonidine is required.