Occipito-Temporal Lesions

    • Focal damage to posterior inferior temporal lobe causing poor visual recognition (“visual agnosia”)
    • Common causes of unilateral lesions: stroke
    • Common causes of bilateral lesions: Alzheimer disease, encephalitis, posterior reversible encephalopathy syndrome (PRES)
    • Visual acuity is preserved with unilateral lesions
    • Tip: visual acuity testing may falsely suggest poor acuity if the patient has pure alexia
    • Right temporal lesion
      • Homonymous hemianopia primarily affecting the left superior quadrants
      • Topographical agnosia (difficulty following familiar routes)
    • Left temporal lesion
      • Homonymous hemianopia primarily affecting the right superior quadrants
      • Inability to read, yet ability to spell and write to dictation (“pure alexia,” “alexia without agraphia”)
    • Bilateral temporal lesions
      • Bilateral homonymous hemianopia primarily affecting the superior quadrants
      • Inability to recognize famous or familiar faces (“prosopagnosia”), colors (“cerebral achromatopsia”), or standard objects (“visual object agnosia”)
    • Reduced level of consciousness
    • Developmental cognitive retardation
    • Delirium
    • Dementia
    • Psychogenic unresponsiveness
    • Poor cooperation
    • Impaired communication
    • Test visual acuity with tumbling Es or pictures in patients with alexia
    • Test for prosopagnosia by displaying famous faces in magazines or by asking patients to identify companions
    • Test for visual object agnosia
      • Instruct patients to identify common objects
        • If patients cannot identify common objects by sight, but can identify those objects by grasping them, diagnose visual object agnosia
        • If patients cannot identify common objects by grasping them, but can describe how those objects are used, diagnose a naming disorder (“dysnomia”)
        • If patients cannot describe how grasped objects are used, diagnose dementia or poor cooperation
    • Test for alexia without agraphia
      • Instruct patients to read common words
        • If patients cannot read common words, but can spell and write them to dictation, diagnose pure alexia (“alexia without agraphia”)
        • If patients cannot spell or write common words, diagnose aphasia, poor cooperation, poor education, or cognitive impairment
    • Diagnosis of recognition deficits is often delayed because standard examinations do not assess them
    • Patient responses are often falsely attributed to poor cooperation, depression, or dementia
    • Alexia falsely suggests reduced vision
    • Deficits may improve in stroke
    • Deficits will worsen in dementia
    • Trap: widely-prescribed rehabilitative measures offer limited benefit