A 70-year-old man presents with h/o prosopagnosia, loss of memory, 3rd person hallucinations since 1 month. On examination deep tendon reflexes are increased, mini-mental examination score is 20/30. What is most likely diagnosis?

The presence of loss of memory, prosopagnosia (difficulty in identifying face) in a 70 year old man is quite suggestive of Alzheimer's disease. Third person auditory hallucinations are usually seen in schizophrenia; however they can be present in Alzheimer's disease too. Fuher on examination, deep tendon reflexes are increased, which again can be seen in late stage of Alzheimer's disease. Finally MMSE score below 24 seals the diagnosis.