Opisthotonus

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Opisthotonus or opisthotonos, from Greek roots, opistho meaning "behind" and tonos meaning "tension", is a state of a severe hyperextension and spasticity in which an individual's head, neck and spinal column enter into a complete "bridging" or "arching" position. This abnormal posturing is an extrapyramidal effect and is caused by spasm of the axial muscles along the spinal column. It is seen in some cases of severe cerebral palsy and traumatic brain injury or as a result of the severe muscular spasms associated with tetanus.

Opisthotonus can be produced experimentally in animals by transection of the midbrain (between superior and inferior colliculus which results in severing all the corticoreticular fibers. Hyperextension occurs because facilitation of anterior reticulospinal tract due to removal of inhibitory corticoreticular fibers to the pons reticular formation.

Infants and children display opisthotonus often more obviously. Opisthotonus in infants may be apparent in the first hours of life, and may be a sign of meningitis. This marked extensor tone can cause infants to "rear backwards" and stiffen out as the mother or nurse attempts to hold or feed them. Opisthotonus can be induced by any attempt at movement such as smiling, feeding, vocalization, or by seizure activity. Individuals with opisthotonus are quite challenging to position, especially in wheelchairs and car seats.