A 52-year-old man with rheumatoid arthritis and no prior psychiatric history develops persistent low mood, anhedonia, fatigue, psychomotor retardation, and hypersomnia three months after starting interferon-alpha therapy for concomitant hepatitis B. His rheumatologist notes elevated IL-6 and TNF-alpha levels. The PMHNP evaluates him for major depressive disorder and considers the neuroinflammation hypothesis.