This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
The most common cause of dementia is 
Select and explain. 
A. Fronto-Temporal dementia, B. Senile dementia, C. Multi-infarct dementia, D. Alzheimer’s disease
D: Alzheimer’s disease
Answer: D: Alzheimer’s disease 
Explanation: Causes of Dementia: 

Alzheimer’s  (most common in >65 years old)
Vascular dementia/Multi-infarct dementia
Lewy body dementia
Fronto-Temporal dementia (50-70 years)
Huntington’s
Traumatic/Dementia pugilistica
Creutzfeldt-Jakob disease

 
Reversible causes of Dementia

Structural brain lesions:- Normal Pressure Hydrocephalus, SubDural Hematoma, Brain Tumors
Alcohol dementia/ Wernicke’s encephalopathy
Vitamin B12 deficiency
Endocrine:- Hypo/Hyper-thyroidism, Hypo-Parathyroidism
Metabolic disorders:- Dyselectrolytemia (Na, Ca, K), hepatic or renal failure
Autoimmune:- Hashimoto’s paraneoplastic encephalopathy (anti- Yo, Hu, Ri)
Infections:- Whipple’s, Lyme disease, Syphilis, HIV dementia.