While depression and apathy are related and may share many characteristics including decreased energy, poor concentration, lack of interest, and psychomotor retardation, there are also certain signs and symptoms that can help distinguish between them. Apathy tends to be more related to motivation, and depression to mood. Apathy presents with decreased motivation, decreased interest, and lack of emotional engagement. In contrast, depression is more likely to present with depressed mood, feelings of guilt and worthlessness, and thoughts of suicide.

Publication reference : van Reekum, R, Stuss, DT, Ostrander, L. Apathy: Why care? J Neuropsychiatry Clin Neurosci. 2005;17(1):7–19.
Reference URL: https://www.ncbi.nlm.nih.gov/pubmed/15746478