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8.2 Epidemiology and Comorbidity

Section Learning Objectives

  • Indicate the prevalence of schizophrenia spectrum disorders.
  • Describe the sex ratios for these disorders.
  • Identify the disorders that are commonly comorbid with schizophrenia spectrum disorders.

8.2.1 Epidemiology

Schizophrenia occurs in approximately 0.3%-0.7% of the general population (APA, 2013). There is some discrepancy between the rates of diagnosis between genders; these differences appear to be related to the emphasis of various symptoms. For example, men typically present with more negative symptoms whereas women present with more mood-related symptoms. Despite gender differences in presentation of symptoms, there appears to be an equal risk for both genders to develop the disorder.

Schizophrenia typically occurs between late teens and mid-30’s, with the onset of the disorder typically occurring slightly earlier for males than for females (APA, 2013). Earlier onset of the disorder is generally predictive of worse overall prognosis. The onset of symptoms is typically gradual, with initial symptoms presenting similarly to depressive disorders; however, some individuals will present with an abrupt presentation of the disorder. Negative symptoms appear to be more predictive of poorer prognosis than other symptoms. This may be due to negative symptoms being the most persistent, and therefore, most difficult to treat. Overall, an estimated 20% of individuals who are diagnosed with schizophrenia report complete recovery of symptoms (APA, 2013).

Schizoaffective disorder, schizophreniform disorder, brief psychotic disorder, and delusional disorder prevalence rates are all significantly less than that of schizophrenia, occurring in less than 0.3% of the general population. While the depressive type of schizoaffective disorder is diagnosed more in females than males, schizophreniform and delusional disorder appear to be diagnosed equally between genders. The gender discrepancy in schizoaffective disorder is likely due to the higher rate of depressive symptoms as seen in females than males because this sex discrepancy is not evident in the bipolar type of the disorder (APA, 2013).

8.2.2 Comorbidity

There is a high comorbidity rate between schizophrenia spectrum disorders and substance abuse disorders. Furthermore, there is some evidence to suggest that the use of various substances (specifically marijuana) may place an individual at an increased risk to develop schizophrenia if the genetic predisposition is also present (Corcoran et al., 2003). Additionally, there appears to be an increase in anxiety-related disorders—specifically obsessive-compulsive disorder and panic disorder—among individuals with schizophrenia than compared to the general public.

It should also be noted that individuals diagnosed with a schizophrenia spectrum disorder are also at an increased risk for associated medical conditions such as weight gain, diabetes, metabolic syndrome, and cardiovascular and pulmonary disease (APA, 2013). This predisposition to various medical conditions is likely related to medications and poor lifestyle choices, and also place individuals at risk for a reduced life expectancy.

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