Alzheimer's and Senile dementia

Alzheimer's noun - A progressive form of presenile dementia that is similar to senile dementia except that it usually starts in the 40s or 50s; first symptoms are impaired memory which is followed by impaired thought and speech and finally complete helplessness.

Senile dementia and Alzheimer's are semantically related. In some cases you can use "Senile dementia" instead a noun "Alzheimer's".

Senile dementia noun - Dementia of the aged; results from degeneration of the brain in the absence of cerebrovascular disease.

Alzheimer's and senile dementia are semantically related. You can use "Alzheimer's" instead a noun phrase "Senile dementia".