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Seeing is not believing
  1. S J Hickman,
  2. D Alvares,
  3. H Crewes,
  4. R J Wise,
  5. A N Gale
  1. Royal Free Hospital, Pond Street, London NW3 2QG, UK
  1. Correspondence to: Simon J Hickman Royal Free Hospital, Pond Street, London NW3 2QG, UK; simonhickmanbtinternet.com

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We describe a case of posterior cortical atrophy presenting with progressive visuoperceptual and visuospatial difficulties, but with no abnormalities on standard ophthalmological examination.

Case report

The patient, a 53 year old right handed woman, with well controlled primary generalised epilepsy, presented to her optometrist with a 1 year history of deterioration in vision. She had particular difficulties with walking downstairs and following text while reading. She could read 6/12+2 RE (with −0.75/−0.25×90 correction) and 6/12+3 (with −0.75 correction) LE. With +2.25 correction she could read N5 slowly with each eye. On subsequent ophthalmological review no significant abnormality was found on examination and no specific diagnosis was made.

Over the following months her vision deteriorated. She reported difficulties following a line while writing and was unable to tell when a glass was full when pouring a drink. Her husband thought that she was unable to see things in her peripheral vision. This culminated in her crashing her car. She did not have any memory difficulties, she had preserved insight, and there had been no change in personality.

On admission to our unit her visual acuity was 6/18 RE and 6/12 LE with the above correction. She was able to read slowly at N5 corrected with each eye but was unable to name any of the Ishihara plate numbers including the test plate, despite being able to name the colours, trace the outline of the numbers with her finger, and read numbers in normal print. Confrontation visual fields were essentially full although she was slow to recognise objects in her peripheral visual fields owing to an apparent narrowing of attention to foveal vision and had optic ataxia, in that she was unable to localise in space, by pointing, objects placed in her peripheral visual fields. On Goldmann perimetry her visual fields appeared somewhat constricted, probably related to her difficulties with attention, but, importantly, no hemianopia was demonstrated (fig 1). Pupillary responses were normal as was fundal examination. On eye movement testing she had broken smooth pursuit eye movements, although she was able to generate voluntary saccades. The rest of the neurological examination was unremarkable.

Figure 1

 Goldmann perimetry (V4e and II2e).

Her mini-mental state examination score was 28/30. She had some deficits in verbal abstract reasoning and made occasional phonemic errors in speech. She had mild dyscalculia and dyspraxia, but she was able to differentiate left from right and name body parts. She had mild memory impairment, although these were mainly in tasks requiring visual input. She demonstrated simultanagnosia in that she was unable to see the whole of a picture and only described parts of it.

On testing with the cortical vision screening test1 she passed the hue discrimination test, the word reading test, face perception test, the crowding test of letter reading and was able to detect the presence of a circle in the shape detection test but was unsure what to say if it was not present. On the symbol acuity test her Snellen equivalent was 6/18 with each eye, despite being able to read text at N5, which suggested that she had more difficulty in identifying shapes than words. She failed tests of shape discrimination and size discrimination to indicate bilateral occipital dysfunction and also failed tests of scattered dot counting and fragmented numbers to indicate right parietal dysfunction.

Blood tests and cerebrospinal fluid examination were both normal. Magnetic resonance imaging demonstrated cerebral atrophy most marked in the both posterior parietal and occipital lobes (fig 2). A diagnosis of posterior cortical atrophy was made.

Figure 2

 FLAIR MRI demonstrating mainly posterior cortical atrophy.

Comment

This woman therefore presented with progressive visuoperceptual and visuospatial difficulties, but had no abnormalities on ophthalmological examination. She had some features of Balint’s syndrome (that is, simultanagnosia and optic ataxia)2 and other cognitive deficits. Her poor distance visual acuity may have been related to her poor visuospatial ability, given her good, albeit slow, near vision. Her inability to recognise any of the Ishihara plates, with otherwise normal colour vision, is probably a reflection of her other visuoperceptual difficulties, which has been reported before in similar patients,3 although difficulty with figure-ground discrimination cannot be excluded.

Posterior cortical atrophy is a clinical and radiological diagnosis based upon the presence of occipitoparietal abnormalities with initially preserved occipitotemporal (face and colour recognition) and anterior cerebral function.4,5 It is thought to be as a result of Alzheimer’s disease, in most cases,5,6 although the syndrome has been described with other pathologies—for example, subcortical gliosis, Creutzfeld-Jakob disease, and progressive multifocal leucoencephalopathy.5,7 Although it is rare, it should be suspected in any patient presenting with visuoperceptual or visuospatial difficulties in the absence of any signs on standard ophthalmological examination. Screening tests for higher visual function deficits can then be employed.1,6,8

The corollary of this is that a patient with an established diagnosis of dementia should be tested for disorders of higher visual function, because a patient with otherwise mild cognitive deficits may still be driving.6

References

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