A previously easy-going, sociable man becomes markedly suspicious, rigid, and difficult to reason with for several weeks, exactly matching the pattern of a specific personality disorder, but this change appeared only during a severe depressive episode and has begun resolving as his mood improves. Before revealing the answer: should this be diagnosed as a personality disorder?
No. The phenomenon's own text is explicit that a pattern resembling a specific personality disorder appearing only during, or shortly after, an episode of illness does not by itself justify the diagnosis, and should be expected to resolve as the episode does — exactly what is described here. A personality disorder requires a longstanding pattern recognisable well before and independent of any particular illness episode.
References
- Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 10, 'Personality Disorders'.