29th January 2024

Differential diagnoses

• Schizophreniform disorder:  all the criteria for Schizophrenia are present for at least one month but less than 6 months in total. Social and interpersonal functioning is affected to a lesser extent compared to Schizophrenia.
• Schizoaffective disorder: The affective symptoms (e.g. depression or mania) and schizophrenic symptoms are present to an equal degree such that it is difficult to distinguish which is more prominent to make a singular diagnosis.
• Psychotic mood disorders: e.g. Mania with psychosis or depression with psychosis. There are prominent mood symptoms (e.g. major depression or mania) in addition to psychotic symptoms such as delusions or hallucinations. You can distinguish Psychotic mood disorders from Schizoaffective disorder based on the timing of the symptoms. In schizoaffective disorder, psychosis is present in the absence of the mood component, whereas, in the alternative, psychosis is present and driven by the significant mood change.
• Substance-induced psychotic disorder: e.g. ketamine, cocaine, amphetamine. Symptoms manifest during the acute period of drug use or alcohol withdrawal and do not persist when the individual is sober.
• Persistent Delusional disorder: the individual has a firm, fixed delusion (for at least 1-month duration) in the absence of other psychotic symptoms such as hallucinations and continues to have adequate social functioning. In addition, the individual should not meet the criteria for an alternative diagnosis.
• Organic causes: Psychosis can occur secondary to a medical condition. It is, therefore, important to ensure a thorough history, including a collateral history, is taken to ensure accurate chronology of symptomology and differentials are considered. Listed below are some medical conditions that can cause psychosis.
  • Delirium
  • Intracranial tumours: occipital or temporal lobe tumours are associated with hallucinations, whereas tumours in the parietal and temporal lobe are more associated with delusions
  • Metabolic disorders: Wilson’s disease
  • Infectious disease: encephalitis
  • Hepato-renal disorders: hepatic encephalopathy, uraemic encephalopathy
  • Neurodegenerative disease: Alzheimer’s, Huntington’s disease, Lewy body dementia

References

• World Health Organisation). ICD-10 classification of mental and behavioural disorders: clinical descriptors and diagnostic guidelines [internet]. World Health Organisation; 1992 [cited 2022 July 14]. Available from: https://apps.who.int/iris/bitstream/handle/10665/37958/9241544228_eng.pdf?sequence=8&isAllowed=y
• World Health Organisation. ICD-10 classification of mental and behavioural disorders: Diagnostic criteria for research [internet]. World Health Organisation; 1993 [cited 2022 July 14]. Available from: https://apps.who.int/iris/bitstream/handle/10665/37108/9241544554.pdf
• UpToDate. Organic causes of psychosis [internet]. 2022 [cited 2022 August 10]. Available from: https://www.uptodate.com/contents/psychosis-in-adults-epidemiology-clinical-manifestations-and-diagnostic-evaluation?search=organic%20causes%20of%20psychosis&sectionRank=1&usage_type=default&anchor=H473103563&source=machineLearning&selectedTitle=1~150&display_rank=1#H473103563