opisthotonus

In tetanus, opisthotonus reflects unopposed motor neuron firing after tetanospasmin cleaves SNARE proteins in inhibitory glycinergic and GABAergic Renshaw interneurons. Generalized tetanus begins with trismus, or lockjaw, from masseter spasm, progresses to risus sardonicus from facial muscle contraction, then to neck and trunk rigidity with opisthotonus, and to laryngospasm and respiratory failure; spasms are triggered by minor stimuli such as noise or touch, and consciousness and sensation remain entirely intact, which is a distinguishing and distressing feature. Autonomic instability with labile blood pressure and arrhythmia is the commonest cause of death in a supported patient. Management is in a dark quiet environment with wound debridement, metronidazole, human tetanus immune globulin to neutralize unbound toxin, benzodiazepines and often neuromuscular blockade with ventilation, magnesium for autonomic instability, and active immunization, since the disease itself does not confer immunity. Opisthotonus also occurs in kernicterus from unconjugated hyperbilirubinaemia depositing in the basal ganglia, and as decerebrate posturing in severe brain injury.