Nigeria, Jan. 23 -- Dr A was a brilliant surgeon. He had worked for many years mentoring residents and training students, and he was highly valued in his department. He also had a sharp and ready wit, ready with the next answer and quick to respond to jabs.

He spoke English, Yoruba and Hausa fluently, although his first language was Yoruba. Everyone knew not to cross him in the department because he had a sharp tongue and would lash out with the most caustic retorts. As he was nearing retirement, he became the head of his department and was saddled with a lot of administrative responsibilities.

His secretary began to notice some lapses in his concentration about a year into his new role. He would forget his keys in the office and be loo...