Hemi-Inattention Presenting as Homonymous Hemianopia in Early Dementia

SIR: Patients with Alzheimer's disease may experience a variety of visual disturbances, including a visuospatial disorder with hemi-inattention, environmental disorientation, and constructional apraxia. Neuropsychological tests of these patients can reveal impaired object/face recognition, complex form discrimination, and spatial localization.¹ This syndrome is associated with neuropathological involvement of the visual association cortex and relative sparing of the primary visual system.² We report a patient who presented with mild dementia and an apparent visual hemifield defect that proved to be hemi-inattention.

Case Report

The patient was a 74-year-old right-handed woman with a 1-year history of difficulties with short-term memory, orientation, and management of finances. At the same time, she began demonstrating other unusual behaviors. The patient cut sandwiches to the extreme right of center and set the dining table with all of the silverware placed to the right of the plate. She approached stairs cautiously, probing ahead with her right foot.

On examination, visual acuity was right 20/25, left 20/30, with correction. Saccades and smooth pursuit eye movements were normal. Visual field testing by confrontation revealed a dense left homonymous hemianopia that was confirmed by automated visual field testing. Her Mini-Mental State Examination score was 24, with errors in orientation, attention, and visuospatial function. Specifically, she failed to copy the left side of interlocking pentagons. Category retrieval and the remainder of the neurologic exam were normal. Medical history was not relevant to the current disorder.

A brain MRI showed moderate, symmetrical, generalized atrophy with proportionate expansion of the ventricles, cortical sulci, and extra-axial spaces. There were a few punctate foci of increased fluid-attenuated inversion recovery (FLAIR) signal in the right caudate and lentiform nuclei consistent with mild cerebrovascular disease. A neuro-opthalmology consultant found left hemi-extinction to double simultaneous stimulation with full visual fields to single stimuli. Goldman perimetry showed intact visual fields. The patient was diagnosed with probable Alzheimer's disease.

Comment

This case illustrates the challenge of differentiating visual field defects from neglect. The discrepant results between automated and Goldman perimetry reflect the slower pace of the latter. Neglect is time-dependent, with an ipsilesional stimulus extinguishing awareness of a subsequent contralesional stimulus for more than 1 second.³ Extinction has been described as a failure to disengage attention from an ipsilesional visual target. Visual extinction on double simultaneous stimulation is a sign of visual neglect; it is a common feature of hemi-inattention and is considered a type of simultanagnosia.⁴ Simultanagnosia and related syndromes are most commonly associated with right parietal lobe injury, reflecting right hemisphere dominance for spatial attention.

A report of a previous series of 10 patients presenting with simultanagnosia and dementia noted these common clinical characteristics: early visual complaints, young age at onset (mean 60 years), no family history of dementia, aphasia with prominent anomia, visuospatial disturbance, and bilateral occipitoparietal atrophy by MRI.⁵ The patient we describe differs with respect to later age at onset (73 years), intact naming function, and the absence of isolated occipitoparietal atrophy on MRI. These differences emphasize the clinical heterogeneity of patients presenting with mild dementia and visual complaints.