"This report describes the successful improvement in symptoms and quality of life in a young man with psychosis and ASD [autism spectrum disorder], who had previously tried numerous medical interventions."
So said the findings published by Victoria Bell and colleagues  (open-access available here) providing some discussion not only about how a diagnosis of autism is seemingly not protective against the development of something like psychosis (see here) but also how psychosis in this context can be successfully managed with a little bit of [clinical] thought. I'll also draw your attention to some other quite recent research that has conversely talked about how difficult it can be to treat psychosis when an autism diagnosis is also in the frame (see here).
Bell et al discuss a case report of a young man (HP) who came to clinical attention in his mid-teens. School examinations seemed to be a possible trigger for episodes of vomiting after eating, leading to hospitalisation. Other symptoms also appeared - "a lowering of mood and poor sleep, and weight loss" - leading to more clinical contact. Bullying was also a feature; as we are told that: "a group of boys had made videos of him, including him being flash mobbed, which had been placed on YouTube; they had also made a persecutory Facebook page." I can think of a few choice words to describe such boys and their antics but won't.
As time progressed, he had "an in-patient admission to a Child and Adolescent Mental Health Services ward, for over a year" where a diagnosis of Asperger syndrome was made alongside "dissociative disorder, and a severe depressive episode with psychotic features." Lots more followed including him becoming "increasingly non-communicative and episodically aggressive toward his parents" culminating in him returning to an in-patient setting.
What is rather refreshing to see is the clinical work-up that this young man received. So: "magnetic resonance imaging (MRI) scans, electroencephalograms (EEGs), anti-NMDA antibodies, as well as B12, folate and thyroid function tests were repeatedly normal." Some critical thinking eventually led clinicians to discount the idea that his symptoms 'were just part of his autism' - "differentiating between psychotic catatonia and autism-related catatonia" - and instead look to a comorbid diagnosis of psychosis. Further: "this was adopted as our working diagnosis for treatment."
Treatment came in the form of various pharmacotherapy and some 'psychological input' bearing in mind "HP remained selectively mute throughout his admission." His clinical management wasn't exactly helped by the fact that another 'very disruptive patient' was admitted at the same time as HP and, on more than one occasion, physically attacked him. But eventually the 'number of days out' increased and symptoms such as vomiting, incontinence and aggression decreased as the "symptom-based approach" adopted seemed to work.
What lessons can be learned from this case report? Well, several. Not least that as well as not existing in some sort of diagnostic vacuum (see here), a diagnosis of autism can and does raise the risk of various psychiatric comorbidity potentially appearing. And sometimes it's hard to see where autism ends and said comorbidity starts (see here for example); assuming that is, that you see comorbidity as comorbidity and not something rather more core.
There is also a positive message from the Bell findings in relation to the 'treatability' of various comorbidity over-represented alongside autism. Yes, it takes time and resources to diagnose and rule things in or out, but quality of life can be improved for the person and those around them. Indeed the authors add: "The level of violence upon admission concerned our team and his parents... if psychotic symptoms were ignored, violence may have continued and led to long-term placements in a more secure environment." Indeed.
 Bell V. et al. A symptom-based approach to treatment of psychosis in autism spectrum disorder in October 2017. BJPsych Open. 2018 Jan;4(1):1-4.