Posterior Cortical Atrophy

A rare neurologic disease characterized by impairment of higher visual processing skills and other posterior cortical functions without any evidence of ocular abnormalities, relatively intact memory and language in the early stages, and atrophy of posterior brain regions.

Epidemiology

Posterior Cortical Atrophy (PCA) prevalence is unknown, largely due to the lack of awareness of the syndrome, delayed diagnosis and the variable terminology referring to it (now partially addressed through international consensus criteria).

Clinical description

Early PCA symptoms include visuoperceptual and visuospatial dysfunction, apraxia and alexia. Features of Bálint syndrome (simultanagnosia, optic ataxia and oculomotor apraxia) and Gerstmann syndrome (acalculia, agraphia, finger agnosia and left-right disorientation) are commonly described. The disorder typical onset is between 50-65 years of age. Earliest reported symptoms include difficulties with complex visual behaviors (e.g. driving, reading, and telling the time from an analogue watch). Reading problems include getting lost on the page (visual disorientation), overlapping or miscombined letters (visual crowding) or better reading of small than large print. Odd visual manifestations like abnormally prolonged color after-images and perception of movement of static stimuli are also reported. People with PCA tend to have relatively well preserved memory, insight, and judgment early in the disease course, though language (word finding problems, phonological errors) often emerge early. It should also be noted that PCA is a relatively heterogenous syndrome with some experiencing a very focal visual syndrome, whilst others show a more mixed cognitive picture with prominent visual but also evident episodic memory deficits from early in the disease course. Individuals with PCA often experience anxiety and depression from early on. Extrapyramidal signs, myoclonus, and grasp reflex have also been reported in PCA patients. An international consensus classification frameworkdistinguishes two syndromic description levels. Classification 1 (PCA) defines the core clinical, cognitive, and neuroimaging features and exclusion criteria of the clinico-radiological syndrome. Classification level 2 (PCA-pure, PCA-plus) establishes whether, in addition to the core PCA syndrome, the core features of any other neurodegenerative syndromes are present.

Etiology

A third level of the international classification framework provides disease-level descriptions of the underlying causes of the PCA syndrome, based on available pathophysiological biomarker evidence. This distinguishes between Alzheimer's disease as the most common underlying pathology (PCA-AD), and other causes including Lewy Body disease (PCA-LBD), corticobasal degeneration (PCA-CBD) and prion disease (PCA-prion).

Diagnostic methods

PCA is an under-recognized disorder resulting often in a significant delay in diagnosis. Diagnosis of this clinico-radiological syndrome is based on neurological assessment, specific visual and cognitive testing, and (optional supportive) brain imaging and routine blood tests. MRI characteristically shows bilateral atrophy in the occipital, parietal and posterior temporal lobes, often asymmetric being more pronounced in the right hemisphere. Single photon emission computed tomography (SPECT) or PET show hypometabolism of the posterior cerebral areas as well as in the frontal eye fields in more advanced stages. Conclusive diagnosis of the underlying disease is confirmed on brain autopsy, though CSF and amyloid imaging may help to refine the clinical diagnosis.

Differential diagnosis

Differential diagnosis includes the most commonly associated neuropathology Alzheimer disease, but may also include Lewy body disease, cortico-basal degeneration, and prion diseases such as Creutzfeldt-Jakob disease.

Management and treatment

There is currently no cure for any of the neurodegenerative conditions that most commonly underly the PCA syndrome. Medications like acetylcholinesterase inhibitors, used in the treatment of Alzheimer's disease, are available and might bring relief for some symptoms. Management of PCA is based on visual aids, rehabilitation programs that include psychoeducation, compensatory strategies, and cognitive exercises to cope with visual disabilities. Antidepressant treatments may benefit individuals with PCA who have relatively preserve insight into their decline and often deal with depression, irritability, frustration and a loss of self-confidence. People with PCA and their caregivers are likely to have different needs to people with more typical presentations of Alzheimer's disease, and may benefit from specialized support groups.

Prognosis

Prognosis is poor as PCA is progressive disorder. Life expectancy after PCA diagnosis is thought to be similar (8-12 years) to individuals affected with Alzheimer's disease.