Case of Pure Agraphia in Kana and Romaji Without Sensorimotor Deficits After a Small Infarct of the Posterior Limb of the Internal Capsule.

Objectives: Infarctions of the posterior limb of the internal capsule (plIC) typically cause contralateral motor deficits. Cases with pure agraphia, writing impairments alone, are rare. We present a case of agraphia as the sole symptom after a small infarction in the anterior portion of the left plIC, which facilitates understanding of the interplay between the subcortical and cortical networks controlling writing.

Methods: This study evaluated a 62-year-old right-handed Japanese man presenting with difficulties in typing and writing. In addition to neuropsychological assessments, diffusion tensor tractography and brain perfusion scintigraphy were used to analyze subcortical-cortical network disruptions.

Results: Neuropsychological tests revealed selective agraphia in Kana and Romaji, characterized by phonological errors, but intact Kanji writing. Neuroimaging revealed disrupted neural fibers connecting the thalamus to the superior and middle frontal gyri and mild hypoperfusion in the middle frontal cortex.

Discussion: Selective impairment of thalamic radiation projecting to the left frontal cortex due to the plIC infarction can result in pure agraphia. Our findings suggest a specific role of the left anterior plIC in writing Kana and Romaji, specifically in sound-to-letter conversion and postorthographic processes. This case underscores the importance of evaluating writing ability in patients with plIC infarctions to avoid overlooking agraphia.