A 55 years old man who worked as a technician developed difficulty findings words 2 years earlier, which has evolved into dysfluency, frequent repetition of remarks and questions, stereotypies (purposeless behaviors or fragments of speech frequently repeated, without regard to context), and echolalia. In the past year, he has also become forgetful and restless, and has developed rigid routines. His work efficiency deteriorated due to his poor comprehension, reasoning, planning, and completion, resulting in disability leave. His wife reports he has became unfeeling, intrusive (indiscriminately approaching strangers), childlike, and impulsive. On the exam, he is pleasant and cooperative. Depression is not evident, and he does not have euphoria, psychosis, or paranoia. Speech is mildly nonfluent and verbal fluency is impaired. Mini-mental state exam score is 29. What is the most likely diagnosis?