Apathy is a specific neuropsychiatric syndrome that is distinct from depression. Apathy is defined as diminished motivation not attributable to decreased level of consciousness, cognitive impairment, or emotional distress. Depression involves considerable emotional distress, evidenced by tearfulness, sadness, anxiety, agitation, insomnia, anorexia, feelings of worthlessness and hopelessness, and recurrent thoughts of death.
http://www.pspinformation.com/disease/depression/apathy.shtml
Depression comes in many forms or types. Each is associated with certain typical symptoms.
http://www.pspinformation.com/disease/depression/depression - types.shtml
Depression is more prevalent in patients who are medically ill. The greater the severity of medical illness, the greater the odds of developing depression.
http://www.pspinformation.com/disease/depression/latelifedepression.shtml