This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Organic mental disorders, Subject name: Psychiatry
All are reversible causes of dementia except 
Select and explain. 
A. Hypothyroidism, B. Hydrocephalus, C. Meningoencephalitis, D. Alzheimer's disease
D: Alzheimer's disease
Answer: D: Alzheimer's disease 
Explanation: Alzheimer&;s is the commonest cause of dementia The diagnosis of Alzheimer&;s dementia is by an exclusion of all other causes of dementia as there is no distinct diagnostic clinical features or laboratory investigations. At present Alzheimer&;s dementia is not considered a treatable disorder (Ref: a sho textbook of psychiatry, Niraj Ahuja, 7th edition, pg no.23)