Schizophrenia: Symptom Overlap

There is considerable overlap between the symptoms of schizophrenia and other conditions, despite the claim that the classification of positive and negative symptoms would make for more valid diagnoses. For example, schizophrenia and bipolar disorder both share positive symptoms like delusions and negative symptoms like avolition. This lack of distinction calls into question the validity of both the classification and diagnosis of schizophrenia. For example, Ellason and Ross (1995) point out that people with dissociative identity disorder (DID) actually have more schizophrenic symptoms than people diagnosed as being schizophrenic! Using the International Classification for Disease (ICD) a patient might be diagnosed as a schizophrenic; however, many of the same patients would receive a diagnosis of bipolar disorder when using DSM criteria. This is not surprising given the symptom overlap: Most people who are diagnosed with schizophrenia have sufficient symptoms of other disorders that they could also receive at least one other diagnosis. Some would argue it suggests that schizophrenia and bipolar disorder may not be two different conditions but one.

Serper et al. (1999) assessed patients with co-morbid schizophrenia and cocaine abuse, cocaine intoxication on its own and schizophrenia on its own. They found that despite there being considerable symptom overlap in patients with schizophrenia and cocaine abuse, it was actually possible to make accurate diagnoses, showing that symptom overlap did not affect the validity of a diagnosis and clinicians can tell the difference between the illnesses.

Ketter (2005) points out that misdiagnosis due to symptom overlap can lead to years of delay in receiving relevant treatment, during which time suffering and further degeneration can occur, as well as high levels of suicide- so symptom overlap can have serious consequences. Focusing on fixing this issue could save money and lives.

Ophoff et al. (2011) assessed genetic material from 50,000 participants to find that of seven gene locations on the genome associated with schizophrenia, three of them were also associated with bipolar disorder, which suggests a genetic overlap between the two disorders and a reason for the symptom overlap. The fact that there is this genetic overlap between the two disorders suggests that gene therapies might be developed which simultaneously treat different illnesses.

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