Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 59, Num. 2, 2011, pp. 297-299

Neurology India, Vol. 59, No. 2, March-April, 2011, pp. 297-299

Letter to Editor

Posterior cortical atrophy: A rare visual variant of Alzheimer's disease

V Abdul Gafoor, James Jose, K Saifudheen, Mohamed Musthafa

Department of Neurology, Medical College, Calicut 8, Kerala, India

Correspondence Address: K Saifudheen, Department of Neurology, Medical College, Calicut 8, Kerala, India drsaifu@yahoo.co.in

Date of Submission: 28-Nov-2010
Date of Decision: 28-Nov-2010
Date of Acceptance: 21-Dec-2010

Code Number: ni11081

PMID: 21483140

DOI: 10.4103/0028-3886.79154

Sir,

The term posterior cortical atrophy (PCA) refers to a clinical syndrome characterized by progressive disruption of higher order visual processing owing to a neurodegenerative disorder. It was first described by Franck Benson in 1988. ^[1] The complex visual disorders seen in PCA patients include elements of Balint's syndrome, apperceptive visual agnosia, alexia, environmental disorientation, simultagnosia, prosopagnosia, and left hemineglect. It is twice common in females. Senile plaques and neurofibrillary tangles constitute the characteristic pathologic findings of PCA and for this reason; some authors use the term "visual variant of Alzheimer's disease (AD)."

A 56-year-old female presented with a 5-year history of insidious onset of difficulty in recognizing familiar faces including that of her family members. However, she could identify them by their voices. Subsequently she developed difficulty in identifying some common objects like household articles. Her speech and writing were normal but she was unable to read. Later, three years into her illness, her family members noticed that she had disregard to objects in the left half of her visual field and for the last 6 months she had difficulty in dressing up by herself. Her behavior and memory were normal and she did not have any dysexecutive symptoms or visuospatial problems. She did not have any hallucinations, weakness, extra pyramidal symptoms, or ataxia. Her past, family and personal histories were insignificant. On examination, she was a right handed, conscious, cooperative, attentive, and cheerful lady. Her Mini Mental Status Examination score was 26/30. Neuropsychological examination revealed marked impairment in the ability to recognize familiar faces, but she was able to provide semantic information about them when their identity was disclosed to her. She also had left hemineglect and constructional apraxia. Elements of Gerstmann's syndrome were present namely, acalculia, alexia, and finger agnosia. She also had Balint's syndrome (simultagnosia, optic ataxia, and ocular motor apraxia). Her visual acuity was 20/100 in both eyes and visual field examination by confrontation revealed left hemineglect. Color vision and funduscopic examination were normal. Her pupils reacted briskly to light and eyes accommodated well to near vision. She did not have any motor or cortical sensory deficits or alien hand phenomenon. Routine blood, urine, serum chemistry, liver, and renal function tests were normal. Magnetic resonance imaging showed marked atrophy of both parietal lobes, with more severe atrophy on right side along with atrophy of both occipital and right temporal lobes [Figure - 1]. Electroencephalogram was normal.

In our patient the first and most disabling symptom was progressive prosopagnosia followed by visual object agnosia. This indicates a disorder affecting the bilateral occipitotemporal (ventral visual stream) cortices. Prosopagnosia has also been described in unilateral lesions affecting the right occipitotemporal cortex or more precisely the right fusiform cortex. ^[2] Subsequent development of Balint's syndrome and components of Gerstmann's syndrome points to the involvement of the bilateral occipitoparietal cortices (dorsal visual stream). Of late, she developed dressing apraxia and left hemi neglect which could suggest right parietal lobe affection. This constellation of findings is suggestive of posterior cortical atrophy or Benson's syndrome, a rare presenile dementia. The diagnostic criteria for PCA have been proposed ^[3] [Table - 1]. The most common pathologic findings of PCA are senile plaques and neurofibrillary tangles predominantly affecting visual association areas. ^[4] But the focal distribution of these changes distinguishes them from typical AD. Magnetic resonance imaging of our patient showed atrophy of occipitoparietal and occipitotemporal cortex with right side being affected more severely. Our patient had prominent atrophy of the right temporal lobe, but she did not have any impairment of episodic memory. Right temporal variant frontotemporal dementia has been described which can also be associated with prosopagnosia. ^[5] But the other manifestations of involvement of visual association areas of brain like Balint syndrome and Gerstmann syndrome are not features of this entity and almost 100% of patients develop inappropriate behaviors as the disease progresses. ^[5] Our patient did not develop any behavioral alterations even after five years of disease duration which argues against a diagnosis of right temporal variant of FTD. Therefore, it can be postulated that the right mesial temporal involvement in our patient is only an extension of the focal cortical degeneration which is a hallmark of PCA.

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