About 97% of Alzheimer’s patients are over the age of 65. Sometimes Alzheimer Disease presents before the age of 65, and has variations in how it first affects patients. Most of these patients are sporadic, in that they do not occur in families, and are probably affected by unknown genetic and environmental variables.
Alzheimer’s can also show up in families. When there are specific genetic mutations involved, the chances of AD are very high. These genetic changes involve gene changes in APP, PSEN1, or PSEN2, but since these changes are so rare, they are not routinely clinically tested for.
A clinical difference between early-onset AD and late-onset AD is that early-onset AD patients have problems with language and visual problems early on, and may have a more prominent history of Traumatic Brain Injury.
These particular clinical problems correlate with Alzheimer’s changes in the brain that are more prominent in the parietal lobes of the brain, with abnormal FDG-PET scans in those areas. Also, Tau protein seems to accumulate early in these same areas.
Amyloid PET scanning is particularly useful in these early AD patients, since early the accumulation of amyloid is characteristic all AD. Spinal fluid analysis, looking at amyloid clearance, is still a research tool in AD.
The so-called “Logopenic” Variant of Primary Progressive Aphasia, with difficulty with word finding and decreased verbal output and difficulty with repetition and comprehension, is one of the clinical presentations of early-AD.
Another clinical variant of early-AD is Posterior Cortical Atrophy (PCA). Patients with PCA have visuo-spatial problems with reading, navigating surroundings, getting dressed, and driving, that seem out of proportion to other deficits. They also have more problems with attention, patterned movements, reading, and executive functions than late-onset AD, and may have a history of repeated visits to ophthalmologists and optometrists because of visual complaints.
Yet another clinical variant if early-onset AD is the behavioral variant, which can sometimes mimic Fronto-Temporal Lobar Degeneration. Apathy, or an absence of willpower, or alternatively impulsiveness, but with prominent memory problems, can all predominate in the clinical picture.
Lastly, calculation difficulties, sometimes accompanied by right-left disorientation and agraphia (problems writing), can predominate. Reading, and carrying out complex actions to command can also be present.
All these clinical characteristics seem to correlate with the involvement of specific areas of the brain by the Alzheimer’s degeneration process, with tau and amyloid plaque accumulation. But problems in these specific areas of performance can also be caused by tumor, infection, inflammation, trauma, vascular disease, and other processes.
This is why a complete evaluation, by an experienced Neurologist, is so important in the management of Alzheimer’s Disease and Dementia. And this is why objective correlates of brain function, like MRI, functional MRI, and PET scanning, have become so important in the evaluation and treatment process of patients with suspected Alzheimer’s Disease.