Guideline 7: Differential Diagnosis The symptoms of schizophrenia often overlap with those of many other psychiatric disorders; thus, the presence of other syndromes should be assessed and ruled out before the diagnosis of schizophrenia can be made. Schizoaffective and mood disorders are commonly confused with schizophrenia,  because they are mistakenly thought to simply include both psychotic and affective symptoms (i.e., in bipolar disorder and major depressive disorder with psychotic features). But it is not the predominance of the psychotic versus the affective component that determines the diagnosis; rather, it is the timing of psychotic and affective symptoms. If psychotic symptoms and affective symptoms always overlap, the person is diagnosed with an affective disorder, whereas if psychotic symptoms are present some of the time, in the absence of an affective syndrome, the person meets criteria for either schizoaffective disorder or schizophrenia (the former, if the mood symptoms are prolonged). Recent research has revealed high rates of exposure to trauma and posttraumatic stress disorder (PTSD) comorbidity among people with a severe mental illness such as schizophrenia (Switzer et al., 1999). These findings, and the overlap in symptom presentation, make PTSD a highly relevant disorder when assessing schizophrenia. Dissociative or intrusive (reexperiencing) symptoms, such as trauma-related auditory phenomena and flashbacks, may be mistakenly interpreted as schizophrenia, so special attention is required to rule them out.

Substance use disorders such as alcohol dependence or drug abuse can either be a differential diagnosis or a comorbid disorder of schizophrenia. With respect to differential diagnosis, substance use disorders can interfere with a clinician’s ability to diagnose schizophrenia, and if the substance use is covert, lead to misdiagnosis (Kranzler et al., 1995). Psychoactive substances, such as alcohol, marijuana, cocaine, and amphetamines, can produce symptoms and dysfunction that mimic those found in schizophrenia, such as hallucinations, delusions, and social withdrawal (Schuckit, 1989). The most critical recommendations for diagnosing substance abuse in schizophrenia include (1) maintain a high index of suspicion of substance abuse, especially if an interviewee has a past history of substance abuse; (2) use multiple assessment techniques, including self-report instruments, interviews with interviewees, clinician reports, reports of significant others, and biological assays; and (3) be alert to signs that may be subtle indicators of the presence of a substance use disorder, such as unexplained symptom relapses, increased familial conflict, money management problems, and depression or suicidality. Many general medical disorders, such as hyperthyroidism, and cognitive disorders, such as dementia of various types, can present with schizophrenia-like symptoms. In many of these disorders the cognitive impairments are similar (e.g., in some cases of Head injury). Hence, the differential diagnosis of schizophrenia in relation to these disorders may be difficult, particularly when past history is not conclusive (e.g., when a first psychotic episode started after a Head injury). Moreover, the impact of comorbidity, such as whether a Head injury that occurred after the onset of schizophrenia is contributing to symptom severity and cognitive impairment, may be very difficult to determine, because the natural course of schizophrenia in itself is not a uniform one. Still, a thorough medical and psychiatric history is helpful in this respect, as are laboratory tests - blood tests for hormones and many other factors, brain imaging such as computed tomography and magnetic resonance imaging, and other tests - to rule out or to confirm general medical and cognitive disorders. Abraham Rundisk David Roe

KEY POINTS

• Schizophrenia is a severe and complex psychiatric disorder; characteristic - positive and negative - symptoms, as well as other impairments, commonly accompany the disorder.
• Diagnostic interviewing for schizophrenia is facilitated by structured assessment tools.
• There are various challenges in diagnostic interviewing of people with schizophrenia, for which guidelines can be helpful.
• Many of the guidelines for diagnostic interviews of people with schizophrenia address clinical communication skills.
• Differential diagnosis should be given special attention in diagnostic interviews of people with schizophrenia.

REFERENCES

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