Posterior cortical atrophy

Posterior cortical atrophy (also known as the Benson syndrome or visual variant of Alzheimer's disease) is a rare neurodegenerative disease which shares pathological and imaging features with Alzheimer disease. 

Epidemiology

No specific demographic has been identified as being particularly at risk and no genetic linkages have been established ¹. As with Alzheimer's disease, patients are typically elderly. 

Clinical presentation

Posterior cortical atrophy is clinically dominated by disruption of normal higher order visual processes, and as such patients eventually behave essentially like individuals who are blind. Patients typically present with ¹:

• visual agnosia : early and pronounced feature
• apraxia: early and pronounced feature
• optic ataxia
• simultanagnosia
• oculomotor apraxia
• prosopagnosia
• alexia
• environmental disorientation

Although mild memory impairment is often present early in the disease, it is clinically different from that seen in Alzheimer's disease ¹. 

Pathology

Neuritic plaques and neurofibrillary tangles are present, especially in parieto-occipital and temporo-occipital areas, and less commonly in the primary visual cortex ¹. As such, posterior cortical atrophy shares features with Alzheimer's disease, so much so that some authors believe it to be a variant of the later, and refer to it as visual variant of Alzheimer's disease. Indeed pathologically the conditions are essentially indistinguishable, other than the distribution of pathological changes. 

Radiographic features

MRI is the modality of choice for assessing patients with neurodegenerative diseases, although CT may allow gross volume changes to be appreciated. Nuclear medicine functional studies are also of benefit. 

MRI

Typical features include ¹:

• bilateral, but often more pronounced right sided, parieto-occipital and temporo-occipital atrophy

Nuclear medicine

SPECT and PET demonstrates hypometabolism in the same areas affected by atrophy ¹. 

Treatment and prognosis

As is the case with most neurodegenerative diseases, no cure is available. Management it medical and centers on behavioural techniques targeted at overcoming visual disabilities as well as antidepressants ¹. 

The disease is gradually progressive with patients usually succumbing within 8 - 12 years from the time of symptom onset ¹. 

Etymology

Posterior cortical atrophy was first described by Franck Benson in 1988, and thus is also known as Benson syndrome ¹. 

Differential diagnosis

The primary differential diagnosis includes:

• Alzheimer's disease
  • clinically very different, with memory is a more pronounced and early feature
  • mesial temporal lobes are spared ¹
• Creutzfeldt-Jakob disease (CJD)
  • clinically CJD has a more rapid time course

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