Hoi Yan is a Junior Medical Officer at Manning Rural Referral Hospital on the Mid-North Coast of New South Wales. She has special interests in endocrinology, general and rural medicine. Originally from Singapore, Hoi Yan moved to Newcastle (Australia) in 2013 to complete her medical degree and has never looked back.
Another Cause Of Visual Impairment
A 66-year-old right handed female presented with a 12-months history of progressive visual problems, memory loss and word finding difficulties on a background of rheumatoid arthritis, depression and osteoporosis. Her medications included methotrexate, folic acid and desvenlafaxine. Ophthalmology and neurology assessments revealed a left sided homonymous hemianopia but CT and MRI brain scans showed no correlating abnormalities. A subsequent single-photon emission computed tomography(SPECT) scan showed hypoperfusion in the right occipito-parietal and posterior-temporal regions.
A geriatrician review identified clinically significant cognitive impairment. She scored 24/30 on the Mini Mental State Examination and 17/30 on the Montreal Cognitive Assessment with points lost in the visuospatial, visuoconstructional and memory domains. She was diagnosed with Posterior Cortical Atrophy(PCA), a variant of Alzheimer’s disease(AD). A trial of Donepezil was commenced and her driving licence suspended.
PCA has a younger age of onset. It is often under-recognised resulting in delayed diagnosis. There is no specific biomarker. Diagnosis of this progressive neurodegenerative condition is based on specific visual testing, neurological examination, appropriate neurocognitive assessments and cerebral imaging. Characteristic bilateral asymmetric atrophy of the occipital, parietal and temporal lobes on MRI supports the diagnosis of PCA. Other neuroimaging modalities such as FDG-PET, amyloid-PET can be helpful in differentiating typical from atypical AD. Neurocognitive assessment identifies early visuospatial, visuoperceptional and memory deficits. Deterioration of language and executive function occur late in the disease.
Conclusion and clinical practise point:
A high index of suspicion for visual variant AD in patients who present with concurrent visual problems and early onset cognitive dysfunction prevents delays in diagnosis. PCA often presents as a diagnostic dilemma because structural neuroimaging can be normal, as in our case. Acetylcholinesterase inhibitors can be considered to improve cognition, but the mainstay in treatment is antidepressants, visual aids and rehabilitation programs to help patients manage their disabilities.