Epidemiology
Schizophrenia is the prototypical psychotic disorder that can include abnormalities in five symptom domains. These domains include hallucinations, delusions, disorganized/abnormal motor behavior, disorganized thinking and/or speech, and negative symptoms (DSM-5, 2017). As Tandon et al. (2013) point out, the definition of schizophrenia has evolved during the time, but the major roots are common for all definitions: emphasis on the poor outcome and chronicity of the disease; notion that dissociative pathology is primary; stress on reality distortion or positive symptoms. Schizophrenia can be diagnosed if one of the following symptoms is present for approximately one month or less if treated successfully:
- Delusions.
- Hallucinations.
- Disorganized speech.
- Grossly disorganized or catatonic behavior.
- Negative symptoms such as avolition, diminished emotional expression, etc. (DSM-5, 2017; Tandon et al., 2013).
Gender differences in schizophrenia and first-episode psychosis need to be considered as well. Although it was previously believed that the incidence and prevalence of schizophrenia in men and women were approximately the same, newer studies point out that the use of more restrictive criteria for diagnosis results in a greater exclusion of women than men (Ochoa, Usall, Cobo, Labad, & Kulkarni, 2012). At the same time, the use of standard diagnostic criteria for schizophrenia confirmed higher incidence in men in a meta-analysis; furthermore, “more new cases of schizophrenia have been detected in men” (Ochoa et al., 2012, p. 2). The mean age of the development of the disease is 18-25 in men and 25-35 in women. Additionally, the disease can be prevalent in women >40 years due to the reduction of estrogens after menopause (Ochoa et al., 2012). Thus, the research provides mixed data on gender differences in schizophrenia.
As to racial and ethnic differences in the prevalence of the disorder, current research indicates that African Americans are more frequently misdiagnosed than Euro-Americans since they are three to five times more likely to be diagnosed with this disorder (Schwartz & Blankenship, 2014). Additionally, one of the researches described by Schwartz and Blankenship (2014) points out that the same prevalence was expected to be among Latino Americans; however, African Americans were still more likely to be diagnosed with schizophrenia than Euro or Latino Americans. Still, Latino Americans’ self-reports contained notions of the high clinical severity of the disorder. However, no empirically verified explanations currently exist that could explain the overrepresentation of African Americans in having schizophrenia. Several explanations exist that could account for this prevalence.
First, the underdiagnosis of major depressive disorder or bipolar disorder in African Americans leads to overdiagnosis of schizophrenia. Clinicians’ race can also contribute to the problem because clinicians of various races apply diagnostic criteria differently. Non-African American clinicians tend to view negative symptoms (anhedonia, motor retardation) as symptoms of schizophrenia, while African American clinicians associate positive symptoms (hallucinations, delusions) with it (Schwartz & Blankenship, 2014). In general, African Americans were more likely to be diagnosed with schizophrenia than Euro Americans or Latino Americans; in European countries, individuals with African descent also had an increased risk of being diagnosed with a psychotic disorder. Nevertheless, current research indicates that the prevalence of schizophrenia around the world is approximately the same; World Health Organization’s (2004) data indicate that the influence of the disease tends to be the highest in Oceania, the Middle East, and East Asia; however, this research is not recent and could change over time.
Risk Factors
Although the causes of schizophrenia are not finally postulated yet, researchers indicate that it is a highly heritable disorder, and genetic risk can be conferred by a large number of alleles (Ripke et al., 2014). Currently, approximately 30 schizophrenia-associated loci were identified through a genome-wide association study (GWAS). However, Ripke et al. (2014) have also provided information about the new 108 independent genomic loci that could also be related to schizophrenia or are of potential therapeutic relevance. Thus, a genetic factor or heredity is the first risk factor for schizophrenia.
Torrey, Bartko, and Yolken (2012) discuss nongenetic risk factors, including infectious ones. One of the main nongenetic factors associated with schizophrenia is Toxoplasma gondii; when it infects pregnant women, it can cause “a congenital syndrome that includes deafness, retinal damage, seizures, and mental retardation” (Torrey et al., 2012, p. 642). If an individual has antibodies to Toxoplasma gondii, it can be an intermediate risk factor for schizophrenia development. Additional risk factors include parental age, family history, maternal exposure to influenza, minor physical anomalies, sex abuse in childhood, urban living in childhood, cannabis use, and immigration. The highest risk factors were having a first-degree relative with schizophrenia or being the offspring of an immigrant from selected countries; intermediate-risk factors were being an immigrant from selected countries, being born or raised in an urban area, cannabis use, and having a father age 55 or older at the time of birth (Torrey et al., 2012). The lowest risk factors were the history of a traumatic brain injury, sex abuse in childhood, obstetrical complications, seasonality of birth, prenatal stress, and maternal exposure to influenza. As can be seen, the development of schizophrenia can be determined by various factors, and many of those are not related to genetic specifics.
Prevalence of Disorder
The prevalence of this disorder is discussed in various studies that mostly have similar results. According to Evensen et al. (2016), 59% of the patients diagnosed with schizophrenia who took part in their study were men. The 12-month prevalence of this disorder was observed in 0.22% of patients older than 18 years. The employment rate among those individuals was 10.24% (Evensen et al., 2016).
Mura, Petretto, Bhat, and Carta (2012) discuss the prevalence of schizophrenia on a larger scale; they point out that the lowest rates of schizophrenia prevalence were reported in Vancouver and Oxfordshire in the UK (less than 0.1 per 1.000) and the highest were observed in Madras and Bavaria (0.58 and 0.48 respectively). They also address the recent male/female ratio in schizophrenia risk, pointing out that the current ratio is 1.2 male to 1 female (Mura et al., 2012). The prevalence of schizophrenia in immigrant populations is also extensively discussed in research; for example, persons of African-Caribbean origin who immigrated in the UK have “an incidence rate 2.5–14.6-fold higher compared to native people” (Mura et al., 2012, p. 55).
Persons of Surinamese origin also have an increased risk of developing severe psychotic disorders if they are five or second-generation immigrants. The incidence risk is the highest during 10-12 years after migration, and it is relatively high in second-generation immigrants as well. It was also reported that the differences in skin color between migrants and the native population could influence the onset of schizophrenia; the bigger the difference, the higher risk of the disorder development. Mura et al. (2012) argue that this factor directly relates to difficulties related to immigration, including isolation, high-stress levels, racism, and discrimination. Socio-environmental factors together with a genetic predisposition may cause the disorder onset.
Behavioral Manifestations
The research divides behavioral manifestations in schizophrenia into two major groups: positive and negative symptoms. According to the National Institute of Mental Health (NIMH) (2016), positive symptoms are psychotic behaviors usually not seen in healthy people, such as hallucinations, delusions, and dysfunctional thinking and movement (e.g., agitated body movements). Negative symptoms include the flat affect (reduced expression of emotions), anhedonia (inability to feel pleasure), inability to begin and/or sustain activities, and reduced speaking (National Institute of Mental Health, 2016). Cognitive symptoms may also be present and include impaired ability to understand information, difficulty focusing, and paying attention, and difficulties in remembering new information and using it after learning.
Auditory verbal hallucinations (AVHs) are included in the first set of symptoms; patients can see, feel, hear, or smell something that others do not, can hear voices that talk to the patient or about them, or with each other. Antipsychotics reduce AVHs, which implies that dopaminergic involvement can be present in these manifestations (Javitt & Sweet, 2015). AVHs also adversely influence the social functioning of individuals as they are often unable to interpret non-verbal information used in conversations (tone and gestures) (Javitt & Sweet, 2015).
Delusions are also common for people with schizophrenia. Delusions are beliefs that appear unreasonable or strange to other people. Patients with schizophrenia can believe that they are being followed or spied on, that they are a robot or other inanimate object, or that they are a famous person (a politician, historical person, actor/actress, etc.). Negative symptoms relate to the reduced expression of emotions, impaired or reduced speaking, and the inability to feel pleasure from everyday activities. Individuals appear to be emotionless, might not talk for days, and do not start any tasks or cannot complete them. One of the radical manifestations of negative symptoms is the inability to feel pain or a high tolerance for it. Antioch et al. (2015) argue that decreased pain sensitivity can relate to the affective flattening and avolition; some examples include individuals with schizophrenia who did not report any pain when they had active gastroduodenal artery bleeding or acute appendicitis. It is supposed that attention and working memory deficit can be responsible for decreased pain sensitivity as well.
The cognitive domain includes impairments in executive attention, as well as in alerting and orienting. Impairments in executive attention only (control of thoughts and actions) are more common among people who experienced first-episode schizophrenia, whereas alerting and orienting impairments (together with executive attention dysfunctions) are usual for chronically ill patients (Orellana, Slachevsky, & Peña, 2012). People with schizophrenia have difficulties in understanding information that is provided to them (e.g., they experience difficulties in following simple instructions), and might be unable to pay attention to this information as well (e.g., lose track of what is happening in a book or TV series while reading/watching). When learning, individuals with schizophrenia have a hard time applying new information in practice as their working memory functions incorrectly (Orellana et al., 2012). As can be seen, schizophrenia manifestations are varied and can take many forms, changing from case to case.
Comorbidity
People with schizophrenia can have different comorbid conditions that include physical and mental illnesses. Among the most widespread comorbid conditions were hypertension (16% of observed cases), chronic pain or pain (13%), dyspepsia (11.4%), T2DM (9%), constipation (9%), thyroid disorders (7.6%), asthma (7.2%), COPD (6%), CHD (5.9%), IBS (5.6), hearing loss (5.1%), and others, including CKD, cancer, and heart failure (3%, 3%, 2% respectively) (Smith, Langan, McLean, Guthrie, & Mercer, 2013). Overall, individuals with schizophrenia were more likely to have one, two, or three physical-health comorbidities compared to individuals without this mental illness.
Another study on comorbid conditions in patients with schizophrenia supports the findings of Smith et al. (2013). However, Schoepf, Uppal, Potluri, and Heun (2013) point out that these individuals are also at risk of developing depression and T2DM, together with alcohol abuse, asthma, and COPD. It should be noted that suicidal and parasuicidal events are also more common among persons with schizophrenia. Parkinsonism, COPD, T2DM, pneumonia, iron-deficiency anemia, ischemic stroke, alcoholic liver disease, and others were among the most relevant risk factors for general hospital mortality among patients with schizophrenia (Schoepf et al., 2013). It should be noted that, in general, patients with schizophrenia had worse outcomes at the end of the study period conducted by Schoepf et al. (2013) compared to the control population. Men with schizophrenia had more negative and less affective symptoms, younger age at onset, and more hospitalizations than female schizophrenic patients. Furthermore, schizophrenic patients also had an increased rate of unplanned hospital admissions, as well as an extended length of stay. Thus, individuals with schizophrenia can have multiple comorbid conditions that can influence their mortality rates.
Differential Diagnoses
Two differential diagnoses will be compared to schizophrenia: psychotic bipolar disorder and psychotic depression. Rosen et al. (2012) point out that positive symptoms of schizophrenia and psychotic bipolar disorder can overlap, but cognitive disorganization (difficulties in abstract thinking and concentration, conceptual disorganization, etc.) was more common among individuals with schizophrenia than those with bipolar disorder or unipolar depression. Positive symptoms such as excitement and paranoia are more common for bipolar disorder with psychosis and schizophrenia rather than unipolar depression with psychosis.
Thought disturbance is also more common both for BD and schizophrenia. At the same time, depression and anergia are seen both in schizophrenia and depression with psychosis. Cognitive symptoms, however, are observed in individuals with schizophrenia only (Rosen et al., 2012). Thus, when reviewing differential diagnoses, it is important for a professional to evaluate cognitive symptoms in a patient (ability to concentrate, understand new information, apply this information, think about abstract topics, etc.) together with negative and positive symptoms. The presence of positive or negative symptoms only might indicate the presence of BD or depression, whereas symptoms regarding the cognitive domain point out the higher probability of first-episode schizophrenia rather than other mental illnesses.
Rosen et al. (2012) stress that to define the boundaries between different psychotic disorders; additional research is needed to better formulate diagnostic differences in the symptomatology of affective and nonaffective psychotic disorders. As the primary symptoms of schizophrenia can overlap with other psychotic disorders, it is important to create more diagnostically specific symptomatology. The research of cognitive symptoms in schizophrenia can potentially increase the accuracy of symptomatology and affect future cases of misdiagnosis among different population groups. The presence of three sets of symptoms (negative, positive, and cognitive) is currently used as a basis for schizophrenia diagnostics.
References
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