Dados do Trabalho

Título

Deconstructing the disconnection syndrome: interhemispheric transfer of information in a ‘pure culture’ of patients undergoing selective section of the posterior corpus callosum

Introdução

Classical neurology teaches that section of the posterior CC should lead to a disconnection syndrome, with dyspraxia, tactile dysphasia and naming difficulties, due to interruption of interhemispheric fibers connecting temporo-parieto-occipital cortices. We have devised a new surgical strategy to control medically refractory drop attacks in which only the posterior half of the CC is sectioned, sparing fibers interconnecting the prefrontal cortices. Because classical teaching is heavily derived from patients in whom the posterior CC is sectioned in the context of more extensive callosotomy, patients undergoing selective posterior callosotomy (SPC) constitute a ‘pure culture’ of individuals with section restricted to the posterior half of the CC.

Objetivo

To test the interhemispheric transfer of information in patients in whom the posterior half of the corpus callosum (CC) was selectively sectioned.

Método

From a series of 34 patients undergoing SPC, 15 right-handed individuals were testable. Object identification from tactile stimuli (stereognosis) and object naming without viewing was tested with simple objects hidden from view behind a cardboard box, with holes for inserting the arms. Correct identification and naming with each hand was independently quantified and timed in seconds. We also probed pre and post-operative autonomy to dress, toilet care, eat, stand straight and walk, sphincter control, reading and fluent speech, from interviews with caregivers in the whole sample and generated a 13-point functional score.

Resultados

From a composite of 5 objects (key, coin, paper clip, small ball, bottle cap) identification and naming was correct in 69.3% of the trials with the left hand and 78.6% with the right hand (NS). Mean time to name a coin and a ball with the left hand was 6s and 4s, respectively, and with the right hand 4s and 6s (NS). Median 13-point functional score increased from 7 to 8 post-operatively (p= 0.03).

Conclusão

Traditional teaching regarding a disconnection syndrome with sectioning of the posterior CC was likely related to complete callosotomy, rather than to posterior section. Because in our patients naming accuracy and speed did not differ with the right and left hands, and there was no worsening in daily functioning, interhemispheric transfer of information was not significantly compromised by SPC. The anatomical basis of the so-called disconnection syndrome should be reviewed, as this is largely prevented by sparing the prefrontal connectivity.

Palavras-chave

Disconnection; callosotomy