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Overlapping symptoms and differences
Psychosis
Psychosis is not a diagnosis in and of itself but rather a cluster of symptoms present in psychotic disorders characterised by a loss of touch with reality. People with these disorders may experience symptoms such as hallucinations, delusions, disorganized thinking, and abnormal behaviour. These symptoms can significantly impact the individual's ability to function in everyday life. Psychotic disorders are often chronic and require ongoing treatment.
In DSM-5, psychotic disorders are classified into different categories based on the specific symptoms and duration of illness: schizophrenia spectrum and other psychotic disorders:
· Schizoaffective disorder is hybrid diagnosis that combines symptoms of schizophrenia and mood disorders like bipolar or depressive disorders. Individuals with this disorder experience psychotic symptoms along with periods of either mania or depression.
· Schizophreniform disorder shares similarities with schizophrenia but differs in duration: if the symptoms last longer than six months, the diagnosis may be changed to schizophrenia.
· Delusional disorder involves the presence of non-bizarre delusions that last for at least one month. Unlike other psychotic disorders, individuals with delusional disorder may not experience significant impairment in functioning.
· Brief psychotic disorder is characterized by a sudden onset of psychotic symptoms that last less than one month. This disorder is often triggered by a stressful event. Despite the short duration, it can have a significant impact on the individual's life.
· Psychotic disorder due to another medical condition
· Bipolar and related disorders with psychotic features
· Substance/medication-induced psychotic disorder. Some substances (e.g., hallucinogens, stimulants or alcohol) and certain prescription medications can induce psychotic symptoms in individuals who use them. Other risk factors for developing this disorder include a family history of psychotic disorders, and certain genetic factors. The symptoms may include hallucinations, delusions, disorganized thinking, and unusual behaviours. These symptoms typically resolve once the substance is cleared from the body or the medication is discontinued.
· Other specified psychotic disorder is diagnosed when an individual experiences psychotic symptoms that do not meet the full criteria for any specific psychotic disorder.
· Unspecified psychotic disorder is another diagnostic category used when an individual experiences psychotic symptoms, but the specific diagnosis cannot be determined or does not fit into any other category.
It is important to differentiate between psychotic and non-psychotic experiences. While many people may experience brief episodes of disordered thinking or mild delusions, psychosis is characterized by more intense and persistent symptoms that significantly impact daily functioning.
Autism Spectrum Disorder
There is a consensus that ASD is extremely heterogeneous clinically and genetically. In fact, ASDs comprise of many complex and clinically distinct neurodevelopmental disorders/conditions with both genetic and environmental components. The diagnosis of ASD, however, relies on behaviours that indicate impairments in social communication and interaction, the presence of restricted and repetitive behavioural patterns and sensory sensitivities. These are categorised into three levels of support the individual requires.
Historical Note
In the 1960s, Kanner’s ‘early infantile autism’ was still considered ‘infantile psychosis’ /’early childhood psychosis,’ or ‘a form of schizophrenia’ /’schizophrenic syndrome of childhood’ (BMJ, 1961). However, the infantile psychosis was a matter for controversy. The psychotic conditions were observed in childhood and increased in frequency during adolescence (Volkmar 1996).The nature of the disorders, their aetiology, relationship to adult forms of psychosis, long-term outcome and response to treatment were areas of disagreement among clinicians (Rutter, Greenfeld, Lockyer 1967).
When ‘infantile autism’ was established as a separate diagnose in DSM-III (1980), the relationship between autism and childhood psychosis was assessed: in comparison to autistic persons, psychotic individuals were judged to have better language and social skills. In addition, autistic persons were also rated as having more difficulty adapting to new situations and appeared more "autistic-like." However, 20% of the psychotic subjects received pervasive developmental disorder diagnoses, indicating that there may be a relationship between those two disorders (Matese, Matson, Sevin 1994).
Overlapping Symptoms and Challenges in Diagnosis
ASD and psychotic disorders are distinct conditions outlined in the DSM-5. However, their overlapping symptoms and frequent co-occurrence pose diagnostic and therapeutic challenges within clinical practice.
Similarities and differences
The clinical features shared by both conditions include unusual thought content, deficits in social interaction, and stereotyped behaviors (De Crescenzo et al. 2019; Hommer & Swedo 2015). Additionally, studies have found social cognitive deficits, a symptom of ASD, in individuals at risk for psychosis (Lavoie et al. 2013; Lee et al. 2015). Autistic individuals have difficulty interacting with others due to social cognition deficits and Theory of Mind. This can cause them to have difficulty understanding social cues and making friends. Similarly, individuals with psychosis may experience a decline in social functioning due to their delusions or hallucinations. Therefore, it can be challenging to differentiate between the two disorders, as both can have symptoms that lead to social dysfunction.
Delusions and hallucinations are characteristics that are common among individuals with psychosis and autism. However, the nature of the delusions and hallucinations differs. In autism, delusions and hallucinations are often sensory-based, or related to an object or routine. On the other hand, in psychosis (without autism), delusions and hallucinations are more complex and abstract, often encompassing themes such as grandiosity or paranoia.
It is crucial to recognize the distinction between these manifestations in order to better understand and address the needs of individuals with these conditions.
In the field of computational neuroscience, several models have been proposed to understand the underlying brain mechanisms that contribute to social cognitive dysfunction and the most common symptoms observed in individuals with psychosis (Adams et al. 2013; Iglesias et al. 2017; Vladusich, 2008).
One proposed cognitive mechanism for psychotic symptoms, such as hallucinations, suggests an abnormal perception resulting from an imbalance between higher-order information processing (i.e., perceptual expectations or previous knowledge) and lower-order perceptual processing of external sensory information (Aleman et al. 2003). These experiences may arise when higher-order cognition takes precedence over lower-order sensory information (Hoffman et al., 2007; Hugdahl, 2009). Similarly, certain symptoms seen in ASD may stem from an imbalance between top-down and bottom-up perceptual processing (Palmer et al., 2015; Van de Cruys et al., 2014).
In this context, some psychotic symptoms can be explained as a failure of top-down predictions (Adams et al. 2013) or an increased emphasis on bottom-up prediction errors (Horga et al. 2014). Conversely, individuals with ASD are highly influenced by lower-order sensory information processing (Grossberg & Seidman 2006).
ASD-Psychosis continuum?
The overlap between ASD and prodromal (initial) symptoms of psychosis is an area of increasing interest (Chisholm et al. 2015; Sampson et al. 2020). Some researchers suggest that these two conditions can be seen as opposite ends of the ASD-Psychosis continuum, with social cognition playing a crucial role (Crespi and Badcock 2008). The ASD-P continuum is influenced by genomic imprinting alterations (Badcock & Crespi 2006), as well as the anatomical structure and function of certain brain regions like the amygdala, hippocampus, and prefrontal cortex (Badcock & Crespi 2006; Baron-Cohen & Belmonte 2005; Burns 2004, 2006; Gisabella et al., 2005).
When considering neuroanatomical markers, particularly brain size, research suggests that the amygdala and hippocampus are larger in ASD during early development compared to typically developing individuals (Schumann et al., 2004). However, this difference tends to disappear as they reach adolescence and adulthood (Cheung et al. 2010; Courchesne et al. 2007). Besides there is evidence indicating brain overgrowth in very young children at high risk of developing psychosis (Gilmore et al. 2010). On the other hand, during adulthood, the brain is smaller in psychotic disorders (Aleman & Kahn 2005; Geuze et al. 2005; Gur et al. 2007; Kuroki et al. 2006). These findings suggest that there are distinct neuroanatomical markers associated with both ASD and psychosis.
Regarding social cognition, it is well-established that ASD affects social interactions, particularly in personal contexts (Baron-Cohen & Belmonte, 2005; Bishop-Fitzpatrick et al., 2017; Rosello et al., 2020). On the other hand, psychotic disorders, particularly those within the schizophrenia spectrum, exhibit abnormalities focused on paranoid interpretation (Harrington et al. 2005b). In fact, a specific connection has been suggested between paranoid delusions and a decline in theory of mind abilities (Harrington et al. 2005a).
ASD and psychotic disorders are believed to be influenced by dysregulated development of the social brain (Abu-Akel et al. 2015; Broks 1997; Burns 2006; Emery 2000; Pourcain et al. 2018; Ziermans et al. 2020). It has been proposed that ASD and psychosis represent opposite ends of a continuum of human cognition, ranging from mentalistic cognition (such as theory of mind) to mechanistic cognition (i.e., interaction with the physical environment) (Badcock 2004; Crespi & Badcock 2008).
According to this model, ASD and psychotic disorders exist as extreme points on a social cognition continuum (Abu-Akel & Bailey 2000; Crespi & Badcock 2008). ASD is associated with underactive mechanistic social cognition, while psychotic disorders are linked to hyperactive mentalistic social cognition. These conditions diverge in opposite directions from typical performance (Abu-Akel & Bailey 2000; Abu-Akel et al. 2015). However, evidence for a diametral association between autism and psychosis is scant (Colizzi et al. 2022). Moreover, the results of some studies do not support this theoretical model, for example, the diametrically opposite bias towards mentalization in the autism-psychosis continuum has not been confirmed (Lisøy et al. 2022).
The precise mechanisms that underlie the relationship between psychosis and ASD are still not fully understood. Gaining a comprehensive understanding of the similarities and distinctions between these two conditions can facilitate accurate diagnosis, implement specific treatment strategies that address individual needs and ultimately lead to improved outcome for autistic individuals and those experiencing psychosis.