Complex sentence: Macmillan believes that establishing any retrospective diagnosis with certainty is difficult, and notes that while Eysenck is one of several authors to have argued that Anna O. suffered from an organic malady, he gives a conflicting account of what the malady was.
Split into simpler sentences: Macmillan believes that establishing any retrospective diagnosis with certainty is difficult. He notes that while Eysenck is one of several authors to have argued that Anna O. suffered from an organic malady, Eysenck gives a conflicting account of what the malady was.