The Hands-Off Evaluation - Posture

The posture and body position at rest should be evaluated and determined as being normal or abnormal.  With reference to lesion localisation, a number of characteristic abnormal postures can be encountered in the evaluation of the emergency neurology patient:

Head tilt – This abnormal head posture is characterized by a rotation of the median plane of the head along the axis of the body resulting in one ear being held lower than the other one).  A head tilt indicates a vestibular disorder (peripheral or central) and occurs as a result of the loss of antigravity muscle tone on one side of the neck. In the dog below, the loss of muscle tone is suggested to be on the left resulting in a left-sided head tilt.     

Head turn – Compared to a head tilt, the median plane of the head remains perpendicular to the ground but the nose is turned to one side.  A head turn is often associated with body turn (pleurothotonus) and circling. These signs (called aversion syndrome) are usually toward the side of a forebrain lesion.   

Note this dog exhibits a profound head turn and body turn.

For more information on head turn, read a recent paper that investigated its value in neurolocalisation.

Decerebrate rigidity – This posture is observed as a result of a rostral brainstem lesion (between the colliculi of the midbrain).  It is characterized by rigid extension of all limbs and opisthotonus (dorsoflexion of the head and neck) associated with stuporous or comatose mental status.

Decerebellate rigidity – The rostral part of the cerebellum is inhibitory to the stretch reflex mechanism of antigravity muscles (extensor muscle tone).  Lesion at this level can result in opisthotonus with the thoracic limb extended (decerebellate posture).  Compared to decerebrate posture, the hips may be flexed by the increased tone in the iliopsoas and mentation remains normal.  This posture is often caused by an acute cerebellar lesion and can sometimes be episodic.

This cat exhibits thoracic limb extensor rigidity and spastic flexion of the pelvic limbs.

Schiff-Sherrington posture – This posture is observed with an acute severe thoracic or cranial lumbar spinal cord lesion.  Such a lesion may interfere with inhibitory ascending neurons that project from the lateral grey matter of the cranial lumbar spinal cord segments cranially to inhibit the thoracic limb extensor muscles.  This posture consists of an extensor hypertonia of the thoracic limbs with retention of voluntary movements, normal conscious proprioception, and flaccid paralysis of the pelvic limbs (despite the fact that the paralysis is caused by direct interference with the upper motor neuron.  This posture is present only in severe and acute lesions but does not have prognostic significance. 

Note this dog with Schiff-Sherrington exhibits rigid thoracic limbs and is awake with flaccid pelvic limbs, which would not be seen with decerebrate rigidity.

Wide-based stance – This posture, as seen below in the Boxer dog, is characteristic of a balance disorder with diseases particularly affecting the cerebellum or vestibular apparatus.