A 31-year-old male has a 7-year history of auditory hallucinations and persecutory delusions. Chart review reveals that during two separate hospitalizations he met full criteria for a major depressive episode lasting 8 weeks and 10 weeks respectively. Between these mood episodes, he continues to hear voices commanding him to hide from government agents and maintains the delusion that his food is poisoned, even when his mood is euthymic. Outside of depressive episodes, he has persistent negative symptoms including flat affect and social withdrawal. His mood episodes have been present for approximately 4 years of his total 7-year illness. Which diagnosis best accounts for this presentation?