A 65 year old male is brought to the outpatient clinic with one year illness characterized by marked forgetfulness, visual hallucination, suspiciousness, personality decline, poor self-care and progressive deterioration in his condition. His Mini-Mental Status Examinations (MMSE)score is 10. his most likely diagnosis is -

Question is straight forward without any confusion. Mini-Mental Status Examination (MMSE) score of 10 suggests definitive cognitive impairment. Amongst the given options only dementia is a cognitive disorder (other are delirium and amnestic disorders). Forgetfulness, personality decline; lack of personal care and low MMSE score suggest the diagnosis of dementia. Delusion and paranoid thoughts (suspiciousness) may also occur in dementia. Hallucinations, though uncommon, may be seen in dementia. So, all the given symptoms and sign are suggestive of dementia. Schizophrenia, mania and depression are not cognitive disorders, therefore MMSE scores are not low in these conditions.