What are the localizations of alexia (acalculia) with agraphia and alexia without agraphia in the brain?

Localization of Alexia with Agraphia and Alexia without Agraphia

Alexia with agraphia is localized to the left angular gyrus in the parietal lobe, while alexia without agraphia results from a disconnection between the visual cortex and language areas due to lesions in the left occipital lobe and splenium of the corpus callosum.

Alexia with Agraphia

Alexia with agraphia is characterized by an acquired inability to both read and write, and has specific neuroanatomical correlates:

• Primarily localized to the left angular gyrus in the dominant (usually left) parietal lobe 1, 2
• Often associated with other language impairments as part of a progressive aphasic syndrome 1
• Frequently occurs with acalculia (difficulty with mathematical calculations) as part of Gerstmann syndrome 2
• May present as part of posterior cortical atrophy syndrome with visuospatial dysfunction 1
• Usually caused by:
  • Alzheimer's disease (most common etiology) 1
  • Sometimes frontotemporal lobar degeneration-corticobasal degeneration (FTLD-CBD) 1
  • Occasionally Lewy body dementia 1

Alexia without Agraphia

Alexia without agraphia (also called pure alexia or word blindness) is a disconnection syndrome with distinct localization:

• Results from the combined effect of two specific lesions:
  • Left occipital lobe damage (causing right homonymous hemianopia) 3, 4
  • Damage to the splenium of the corpus callosum 3, 4, 5
• This disconnects visual information from the right visual field (processed by the right occipital lobe) from reaching the language areas in the left hemisphere 3, 6, 4
• The patient can still write because the language areas are intact, but cannot read their own writing 3, 5
• Most commonly caused by occlusion of the left posterior cerebral artery 4, 5
• Can also result from any lesion affecting the splenium of corpus callosum that disrupts white matter tracts from visual cortex to angular gyrus 4

Clinical Distinctions and Associated Findings

• Alexia with agraphia:

  • Often part of a broader language disorder 1
  • Frequently accompanied by other elements of Gerstmann syndrome (finger agnosia, right-left disorientation, acalculia) 2
  • May present with additional posterior cortical symptoms like limb apraxia 1

• Alexia without agraphia:

  • Almost always accompanied by right homonymous hemianopia 3, 5
  • May be associated with color agnosia 6
  • Can present with prosopagnosia (inability to recognize faces) 6
  • Sometimes accompanied by simultanagnosia (inability to perceive the visual field as a whole) 6

Diagnostic Considerations

• Patients with alexia without agraphia may be misdiagnosed as having dementia due to initial confusion and disorientation 6
• Careful language evaluation is essential in patients with homonymous visual field defects to avoid missing alexia 3
• Neuroimaging (MRI) is crucial to identify the specific lesion locations:
  • Left angular gyrus in alexia with agraphia 1, 2
  • Left occipital lobe and splenium of corpus callosum in alexia without agraphia 3, 4, 5

Clinical Implications

• Early recognition of these syndromes is important for appropriate rehabilitation planning 6
• Patients with alexia without agraphia may benefit from specific reading rehabilitation techniques despite being initially thought unsuitable for rehabilitation 6
• The presence of alexia with agraphia may indicate underlying neurodegenerative disease requiring comprehensive management 1