Posterior cortical atrophy (PCA), also known as the Benson's syndrome or visual variant of Alzheimer's disease, is a rare neurodegenerative disease which shares pathological features with Alzheimer disease.
No specific demographic has been identified as being particularly at risk and no genetic linkages have been established. As with Alzheimer's disease, patients are typically elderly.
There are no consistent diagnostic criteria and the entity is likely under recognized 4.
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:
- visual agnosia: early and pronounced feature
- apraxia: early and pronounced feature
- optic ataxia
- simultanagnosia (inability to perceive more than one object at a time)
- oculomotor apraxia
- prosopagnosia (inability to recognize familiar faces)
- alexia (difficulty reading)
- environmental disorientation
Approximately 25% of patients with PCA will also develop visual hallucinations 1.
Although mild memory impairment is often present early in the disease, it is clinically different from that seen in Alzheimer's disease.
Focal degeneration with presence of neuritic plaques and neurofibrillary tangles, especially in parieto-occipital and temporo-occipital areas, and less commonly in the primary visual cortex 4. 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.
Patients with visual hallucinations (~25%) may represent a distinct sub-group, with hallucinations believed to be due to the complex interplay between the midbrain, thalamus and primary visual cortex, rather than the visual association areas 1.
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 4.
Typical features include:
- bilateral, but often more pronounced right sided, parieto-occipital and temporo-occipital atrophy
SPECT and PET demonstrates hypometabolism in the same areas affected by atrophy 4.
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.
The disease is gradually progressive with patients usually succumbing within 8-12 years from the time of symptom onset.
History and etymology
Posterior cortical atrophy was first described by Franck D Benson in 1988, and thus is also known as Benson syndrome 2.
The primary differential diagnosis includes:
- 1. Josephs KA, Whitwell JL, Boeve BF et-al. Visual hallucinations in posterior cortical atrophy. Arch. Neurol. 2006;63 (10): 1427-32. doi:10.1001/archneur.63.10.1427 - Free text at pubmed - Pubmed citation
- 2. Benson DF, Davis RJ, Snyder BD. Posterior cortical atrophy. Arch. Neurol. 1988;45 (7): 789-93. Pubmed citation
- 3. Aharon-Peretz J, Israel O, Goldsher D et-al. Posterior cortical atrophy variants of Alzheimer's disease. Dement Geriatr Cogn Disord. 2000;10 (6): 483-7. doi:17194 - Pubmed citation
- 4. Crutch SJ, Lehmann M, Schott JM et-al. Posterior cortical atrophy. Lancet Neurol. 2012;11 (2): 170-8. doi:10.1016/S1474-4422(11)70289-7 - Free text at pubmed - Pubmed citation
Neurodegenerative diseases are legion and their classification just as protean. A useful approach is to divide them according to underlying pathological process, although even using this schema, there is much overlap and thus resulting confusion.
neurodegenerative MRI brain (an approach)
- measurements and ratios
- midbrain to pons area ratio (for PSP)
- Magnetic Resonance Parkinsonism Index (MRPI) (for PSP)
- frontal horn width to intercaudate distance ratio (FH/CC) (for Huntington disease)
- intercaudate distance to inner table width ratio (CC/IT) (for Huntington disease)
- scoring systems
- measurements and ratios
- typical/classical Alzheimer disease
- variant (e.g. posterior cortical atrophy)
- chronic traumatic encephalopathy (CTE)
- corticobasal degeneration
- frontotemporal lobar degeneration (FTLD) (not all are tau)
- Pick disease
- progressive supranuclear palsy (PSP)
- Alzheimer disease
- cerebral amyloidosis
- spinocerebellar ataxias
- Huntington disease
- hereditary spastic paraplegia
- amyotrophic lateral sclerosis (ALS)
- clinically unclassifiable parkinsonism (CUP)
- Unverricht-Lundborg disease
- prion diseases (not always included as neurodegenerative)