Pearls & Oy-sters: Visual agnosia

PEARL

• Dorsal simultanagnosia is a sign of biparietal cortical pathology. When found in combination with a hypokinetic-rigid syndrome, corticobasal degeneration should be considered.

OY-STERS

• Patients will often not complain of subtle visual processing deficits. If neuropsychological testing is not performed, these deficits will go unnoticed.

• Confrontation naming can be impaired for different reasons: the presence of nonfluent aphasia in this patient cannot explain the partonomic errors.

We report a 77-year-old patient with visual agnosia as a cortical sign of neurodegenerative disease.

The patient presented with balance problems and frequent falls since age 72 and subsequent nonfluent aphasia. Clinical examination revealed a supranuclear vertical gaze palsy and a symmetrical hypokinetic-rigid syndrome. MRI of the cerebrum demonstrated enlargement of the left Sylvian fissure and bilateral intraparietal sulci as well as a hummingbird sign (figure 1, A–D). DaTscan showed bilateral reduced uptake (figure 1E). This clinical phenotype is suggestive of progressive supranuclear palsy.¹

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Figure 1 MRI and DaTscan

(A) Coronal MRI slice: asymmetric enlargement of the left Sylvian fissure (arrow). (B) Coronal MRI slices: enlargement of the bilateral intraparietal sulci (arrows). Note that the temporal cortex is relatively spared. (C) Axial MRI slice: enlargement of the bilateral intraparietal sulci (arrows). (D) Sagittal MRI slice: hummingbird sign. (E) DaTscan: bilateral reduced uptake.

Neuropsychological testing revealed executive dysfunction. The patient, whose vision was corrected to normal with glasses, scored 8/15 on an abbreviated version of the Boston Naming Test. He produced 2 partonomic errors: instead of a tree, he saw leaves, instead of a flower, he saw a branch. He called a hammock a bed, a camel a giraffe, a mask a clown. He could not identify a funnel and tongs. Naming errors due to nonfluent aphasia are typically phonetic errors. Partonomic errors during confrontation naming are visual in nature and indicate a deficit of recognition rather than of name retrieval. This is suggestive of visual agnosia.

When asked to copy the drawings of the Boston Naming Test, the patient omitted several salient surface features (figure 2). The inability of our patient to copy drawings suggests that he has dorsal simultanagnosia rather than ventral simultanagnosia. Both types of simultanagnosia lead to object identification deficits. In dorsal simultanagnosia, the naming errors occur because the patient does not perceive the picture in its entirety. Therefore, a patient with dorsal simultanagnosia will be impaired when asked to copy a drawing. In ventral simultanagnosia, the picture is perceived in its entirety, but it cannot be identified as a whole. This explains why a patient with ventral simultanagnosia can copy a drawing.²

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Figure 2 Copy drawing of the Boston Naming Test

Several visuoperceptual errors were documented when the patient copied the Boston Naming Test. The left column shows the probe picture, the right column shows the drawing made by the patient. Flower: placement error: no leaves are found on the left side. House: placement error of the top right window; salient features, e.g., chimneys, were not copied; the shape of the roof is inaccurate. Tongs: faulty perspective, inaccurately overlapping shapes. Whistle: faulty perspective, surface features are omitted.

Dorsal simultanagnosia is part of a Bálint syndrome, together with optic ataxia and ocular apraxia. Dorsal simultanagnosia can arise due to biparietal damage secondary to structural pathology or neurodegenerative disease, e.g., corticobasal degeneration, posterior cortical atrophy, or Creutzfeldt-Jakob disease. In our patient, the working hypothesis is corticobasal degeneration.³ Given the initial clinical presentation suggestive of progressive supranuclear palsy, our patient adds to the growing phenotypic spectrum of tauopathies.⁴