How to differentiate hemianesthesia from left tactile neglect: a preliminary case report

When assessing for the presence of hemianesthesia, the examiner touches the body of the patients, and requests that they report verbally the location of the delivered tactile stimulus. Contralesional omissions of single tactile stimuli, however, might be due to either primary somatosensory deficits or to spatial attention impairment (i.e., neglect). In this preliminary study, we tested whether clinical assessment can be improved to differentiate between these two types of deficit by modifying the assessment procedure. K.L., a patient with left unilateral neglect, was asked to detect tactile stimuli delivered in two conditions: spatial attention distributed either to his left or to his right hand, and spatial attention focused only on his left hand. Note that K.L. did not receive double simultaneous tactile stimuli. In the distributed spatial attention condition, K.L. omitted most of the single tactile stimuli delivered to his left hand. In the focused attention condition, K.L. was asked to focus his spatial attention only on his left hand. Under this latter condition, his performance increased dramatically, suggesting that his omissions were not due to hemianesthesia, but rather reflected left tactile neglect. In line with the neuropsychological findings, voxel based analysis of his grey and white matter damage confirmed significant loss in areas associated with left-sided neglect, but sparing of the primary somatosensory cortex. This result suggests that standard somatosensory assessment and differential diagnosis between hemianesthesia and tactile neglect may be more accurate when neuropsychology-based procedures are incorporated in the standard neurological examination.