Differential diagnosis

• neurotic illness or a personality problem easily be mistaken when it presents as apathy and failing motivation, or agitated and demanding behaviour, or hypochondriacal complaints.
• dementia - the patient may present with impairment of concentration and memory loss which may be dismissed as demented.(1)
• primary paranoid illness may be considered if the patient has depressive delusional ideas.
• alcoholism is an important feature to rule out
• grief - this is an inherent trait of the human experience and should not be interpreted as a major depressive episode unless it fulfils clinical depression criteria.

Reference

1. Byers AL, Yaffe K. Depression and risk of developing dementia. Nat Rev Neurol. 2011 May 03;7(6):323-31