The Technicalities of Diagnostic Decisions

There are formal methods that should be followed in making the appropriate diagnosis.  Approaching diagnostic decision making professionally and conscientiously aids in proper diagnosis.  A symptom or sign can mean many different things and can come from many different sources.  Consequently, to find out the meaning and source, the clinician engages in differential diagnosis.  Essentially, this means that the clinician considers all the potential explanations for a problem and then slowly eliminates them until only one is left.  This diagnostic decision-making process is described in six steps by First, Frances and Pincus in their book The DSM-IV Handbook of Differential Diagnosis:

1. Ruling out malingering/factitious disorders (faking a disorder)
2. Ruling out substance etiology (drug use)
3. Ruling out an etiological general medical condition
4. Determining the specific primary disorder
5. Ruling out adjustment disorder (a temporary problem adapting to new circumstances)
6. Establishing boundaries with no mental disorder

Now to take an example; suppose someone is experiencing hallucinations (perhaps they are hearing voices or seeing things that are not really there)…this is how these six steps would be used to determine the source of the hallucinations:

1. Are the hallucinations due to the direct effects of a medical condition, such diagnoses might be delirium due to a general medical condition or dementia due to a general medical condition, such as stroke, brain injury or Alzheimer’s disease?
2. Are the hallucinations due to the direct effects of substance use, whether intoxication or withdrawal?
3. If neither of the above, one asks, are these hallucinations accompanied with or without insight…in other words, does the patient know that the voices or vision are fake?
4. Are the hallucinations culturally sanctioned…consider whether this is a mental disorder or an outgrowth of a cultural custom or religious practice.
5. Do hallucinations occur exclusively during the episode of mood disorder…in other words, does the person only hallucinate when she is depressed?
6. If the answer to all of these questions is no, then it is likely that the patient is presenting with some sort of psychotic disorder: Schizophrenia, Schizophreniform Disorder, Schizoaffective Disorder, Psychotic Disorder NOS, Brief Psychotic Disorder

Notice that hallucinations do not invariably come from schizophrenia or even a mental illness.  However, if the hallucinations are symptomatic of a mental illness, the clinician must determine the exact type of mental illness. Step six is complicated and requires the final determination of a firm diagnosis.
First, one can differentiate between these disorders based on duration.  If the duration is less than one day…few hours of hallucination (remembering that substances and medical conditions, etc. have been ruled out) then one can only diagnose Psychotic Disorder Not Otherwise Specified.  If the hallucinations are present for more than one day but less than one month, Brief Psychotic Disorder becomes the logical option.  If hallucination symptoms 1) last for more than a month, 2) if they are present in the absence of mood symptoms, 3) if they are accompanied by disorganization in speech and behavior, then it is one of the following two disorders: Schizophrenia or Schizophreniform Disorder.  The best way to distinguish between these two is again is by duration…Schizophreniform disorder lasts between one and six months, schizophrenia is longer than six months. 

This example shows why formal diagnosis is important.  A single symptom can have so many underlying causes, and each of these causes can have distinct treatment courses.  If hallucinations stem from drug use, detoxification and rehabilitation must follow.  If hallucinations stem from Alzheimer’s disease, medical consultation and long term care options should be reviewed.  If hallucinations are simply a product of religious custom, no treatment is required.  If hallucinations are a symptom of a major depressive episode, a psychiatric consultation and cognitive behavioral therapy should be arranged.