Isolated thalamic agraphia with impaired grapheme formation and micrographia

Abstract

Two patients with isolated thalamic agraphia are described. Both showed kanji (Japanese morphograms) agraphia due to impaired character recall, grapheme deformity and micrographia (progressive reduction in character size during writing) after a lesion that involved the ventral lateral and ventroposterolateral nuclei. Single photon emission computed tomography with a (99m)Tc-ethylcysteinate dimer revealed hypoperfusion in the left precentral gyrus (Brodmann Area 6) and anterior supramarginal gyrus in both. Six months later, the extent of blood flow reduction decreased in the supramarginal gyrus in both patients and the precentral gyrus in patient 1. By this time, the writing impairment improved to nearly the normal range. Our study suggests that kanji agraphia (corresponding to lexical agraphia in Western countries) with poor grapheme formation and micrographia arises from a lesion in the ventral lateral and ventroposterolateral nuclei in the left thalamus. The accompaniment of poor grapheme formation and micrographia may reflect disruption of the cortico-subcortical motor circuit involving the putamen, thalamus, premotor cortex and sensorimotor cortex. It is also suggested that multiple cortical sites can be a target for secondary dysfunction that yields agraphia in a thalamic lesion, and that the recovery of reduced cortical blood flow does not always proceed in parallel with that of agraphia.

Thalamic alexia with agraphia

“…, a diaschisis phenomenon). 22,30 Similar to our patient, previously reported cases of pure apraxic agraphia, 31 pure agraphia, 23,32,33 and alexia with agraphia 11 due to a thalamic lesion have shown hypofunction in the ipsilateral cerebral hemisphere. Araki et al , reported two patients with alexia with agraphia due to left thalamic strokes involving the territory of the tuberothalamic and paramedian arteries (lesion involved the DM nucleus in both cases).…”

“…Cognitive impairment may be a secondary consequence of a deactivated or disengaged cortex. 22 The diaschisis phenomenon in thalamic hemorrhages may be temporary, with gradual improvement in the function of the affected area, 23 but can also be persistent. 24 …”

Brainstem arteriovenous malformation presenting with dyspraxic handwriting in a young girl

“…The thalamic involvement in this girl brings us back to the few reported cases of adult patients with isolated thalamic agraphia with impaired grapheme formation and micrographia due to a lesion in ventral and ventroposterolateral nuclei in the left thalamus or with pure agraphia or with alexia and agraphia due to left thalamic bleeding [2][3][4]. All these authors suggest a potential role of the thalamus in writing disorders with secondary negative effect of the lesion on the function of left cerebral cortex.…”

Cerebral Activations Related to Writing and Drawing with Each Hand

“…The putamen segregation between simple and complex movements would fit a general organization of parallel cortico-basal ganglia loops described for motor and non-motor functions [ 94 ]. The left thalamic activations that were seen not only in right- but also in left-hand writing, contrasted to tapping, points at an aspect of writing beyond movement characteristics [ 95 – 97 ]. Such left thalamic function is anatomically consistent with its position as an outflow target of the right cerebellum and would thus functionally mediate non-motor functions of right posterior cerebellar lobe as described in the previous paragraph.…”