Alzheimer’s Disease is a progressive neurodegenerative disorder that is the most common cause of dementia. It is estimated to affect at least 44 million people worldwide, and over 700,000 in Canada alone. The exact pathophysiology is unknown; however, all types of Alzheimer’s disease have an issue with overproduction and/or reduced clearance of amyloid beta peptides, with the hippocampus and other medial temporal lobe structures affected first.
Alzheimer’s symptoms are most commonly seen in adults over 60, although very rarely, symptoms can occur before the age of 60. Initially, memory impairment is the most common symptom, specifically anterograde long-term episodic amnesia, followed by deficits in executive function and Visuospatial impairment. Behavioural changes and language impairments are typically seen later in the disease course.
MRI imaging can help with excluding other causes of dementia, and assess the overall volume of specific regions of the brain. On MRI, mesial temporal lobe atrophy is seen in Alzheimer’s Disease, and can be ideally measured by directly assessing parahippocampal or hippocampal volume loss. Although not as sensitive, indirect measurement can be done by assessing the enlargement of parahippocampal fissures. In Benson Syndrome, or the posterior cortical atrophy, or early-onset Alzheimer’s disease, temporoparietal cortical atrophy can be seen by examining the posterior cingulate sulcus, parieto-occipital sulcus, parietal lobes, and precuneus gyrus. This has been developed into the Koedam score or posterior atrophy score.
References:
1. https://www.uptodate.com/contents/clinical-features-and-diagnosis-of-alzheimer-disease?search=alzheimers&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
2. https://www.uptodate.com/contents/epidemiology-pathology-and-pathogenesis-of-alzheimer-diseasesectionName=INCIDENCE%20AND%20PREVALENCE&topicRef=5071&anchor=H617807629&source=see_link#H1817000228
3. https://www.nia.nih.gov/health/what-alzheimers-disease
4. https://www.alz.org/ca/dementia-alzheimers-canada.asp#symptoms
5. https://emedicine.medscape.com/article/336281-overview
6. https://radiopaedia.org/articles/alzheimer-disease-1
7. Koedam EL, Lehmann M, van der Flier WM et-al. Visual assessment of posterior atrophy development of a MRI rating scale. Eur Radiol. 2011;21 (12): 2618-25. doi:10.1007/s00330-011-2205-4 -
8. Lehmann M, Koedam EL, Barnes J et-al. Posterior cerebral atrophy in the absence of medial temporal lobe atrophy in pathologically-confirmed Alzheimer's disease. Neurobiol. Aging. 2012;33 (3): 627.e1-627.e12. doi:10.1016/j.neurobiolaging.2011.04.003