Abstract
An ambidextrous female patient with callosal infarction showed agraphia that exhibited different features in the left and right hands. Several reports of previous cases of unilateral left agraphia following callosal damage in a right-handed patient have been described. In this case, agraphia was peculiar as it was observed in both hands. The agraphia of her left hand was characterized mainly by paragraphia including mirror paragraphia, while her right-handed writing showed prominent scrawl and distortion of characters.
Two days after her stroke, a brain MRI revealed an abnormal signal intensity area in the left cingulate gyrus and the corpus callosum except for part of the splenium. Because left unilateral tactile anomia and right constructional disorder was observed in the patient, we hypothesize that in this case language function is predominantly lateralized in the left hemisphere, and that constructional ability of letter shaping is predominantly lateralized in the right hemisphere. The paragraphia including mirror paragraphia observed in the left hand suggests that incomplete character information and motor engram for writing also exist in the right hemisphere. The agraphia of her right hand can be interpreted as the effect of disconnecting the motor information for writing of characters and the constructional ability of letter shaping in the right hemisphere using the information in the left hemisphere. Furthermore, we suspect that the motor engram for writing of characters is stored more strongly in the right hemisphere. The interhemispheric transfer and integration of information between the right and left hemispheres was incomplete probably due to a callosal disconnection, resulting in the agraphia that affected both hands. This report discusses the apparent mechanisms of her agraphia and the hemispheric lateralization of her writing function.
