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Opisthotonos

Opisthotonos is an abnormal posture consisting of arching of the back and extension of the limbs such that the body may be supported just on the head and ankles (arc de cercle).

Opisthotonos may be seen in: Coma; decerebrate rigidity Basilar meningitis Hydrocephalus
Structural lesions of the posterior fossa
Cerebellar fits due to intermittent tonsillar herniation
Acute drug(neuroleptic-) induced dystonic reaction; or chronic feature of tardive dystonia
Tetanus
Syncope (especially in children)
Metabolic disorders: kernicterus, Gaucher’s disease (type II) Drug-induced: propofol
Pseudoseizures

As in decerebrate rigidity, opisthotonos may reflect unopposed extensor tone from the intact vestibular nuclei released from supratentorial control.