Schizophrenia vs. Delusional Disorder

For the past 15 years, my aunt has become paranoid, distrustful, and angry.  She has difficulty sleeping, for years she refused to leave the house, and she believes that a secret society is controlling her and her family.  She also gets into fights with everyone, although she is not a threat to herself or her family.  The weird part is that if you didn’t know her, she would seem perfectly normal - it’s as if she has two different personalities.  She can be very loving, supportive and encourage at times.  At other times she’s argumentative, nasty, controlling and insulting.  She does not drink, smoke, or take drugs or medication.  Can you help me figure out what disorder fits her personality?  Is this paranoid schizophrenia?

It sounds like you and your aunt are going through a difficult time right now.  A family doctor or a psychiatrist would be a good place to start having a discussion as to how best to help the situation, because the number of possible disorders that could cause these symptoms is very large.  Take a look at my earlier blogs on hallucinations and late-onset schizophrenia to give you some idea of what her condition could possibly be.  

This question does give me the opportunity to discuss a topic that often isn’t considered in these types of situations: delusional disorder.  
    
Delusional disorder is an illness in which the patient has elaborate, non-bizarre delusions and expresses emotions consistent with their beliefs.  People with this disorder usually retain their previous personality, but the delusion causes them suffering as it increasingly occupies their mind and takes over more and more of their life. 
   
Unlike schizophrenia, delusional disorder usually does not cause hallucinations.  Individuals with this condition tend to retain organized thinking.  They are also usually emotionally expressive, and report feelings that are consistent with their perception of what is going on in the world.  The central feature of this illness is the delusional system.  Unlike most beliefs associated with schizophrenia, these delusions are usually elaborate and make a lot of sense to the patient.  The delusions are also less odd or absurd than the delusions reported by individuals with schizophrenia (e.g., believing a microtransmitter has been implanted into a person’s body).  People with delusional disorder believe something that is logical, almost plausible, and incorporate these delusions into their real-life experiences and situations.  For example, an elderly man living in an apartment alone may have a neighbor living upstairs who regularly cooks pastries.  The man may develop a delusional system in which he believes that the fumes from the cooking are displacing the oxygen in the air and constricting his air supply.  As a result, he keeps his windows open, at first for a few hours at a time, then all the time, then he begins leaving his door wide open.  It may extend to the point where the man will leave his home because he doesn’t think he can breathe in the room with the presence of all the fumes.