Mapping multimorbidity in individuals with schizophrenia and bipolar disorders: evidence from the South London and Maudsley NHS Foundation Trust Biomedical Research Centre (SLAM BRC) case register

Abstract

Objectives: The first aim of this study was to design and develop a valid and replicable strategy to extract physical health conditions from clinical notes which are common in mental health services. Then, we examined the prevalence of these conditions in individuals with severe mental illness (SMI) and compared their individual and combined prevalence in individuals with bipolar (BD) and schizophrenia spectrum disorders (SSD).

Design: Observational study.

Setting: Secondary mental healthcare services from South London PARTICIPANTS: Our maximal sample comprised 17 500 individuals aged 15 years or older who had received a primary or secondary SMI diagnosis (International Classification of Diseases, 10th edition, F20-31) between 2007 and 2018.

Measures: We designed and implemented a data extraction strategy for 21 common physical comorbidities using a natural language processing pipeline, MedCAT. Associations were investigated with sex, age at SMI diagnosis, ethnicity and social deprivation for the whole cohort and the BD and SSD subgroups. Linear regression models were used to examine associations with disability measured by the Health of Nations Outcome Scale.

Results: Physical health data were extracted, achieving precision rates (F1) above 0.90 for all conditions. The 10 most prevalent conditions were diabetes, hypertension, asthma, arthritis, epilepsy, cerebrovascular accident, eczema, migraine, ischaemic heart disease and chronic obstructive pulmonary disease. The most prevalent combination in this population included diabetes, hypertension and asthma, regardless of their SMI diagnoses.

Conclusions: Our data extraction strategy was found to be adequate to extract physical health data from clinical notes, which is essential for future multimorbidity research using text records. We found that around 40% of our cohort had multimorbidity from which 20% had complex multimorbidity (two or more physical conditions besides SMI). Sex, age, ethnicity and social deprivation were found to be key to understand their heterogeneity and their differential contribution to disability levels in this population. These outputs have direct implications for researchers and clinicians.

Keywords: epidemiology; health informatics; mental health; psychiatry; public health.

Figure 1

Comparison of number of physical health comorbidities (A) and specific physical comorbidities (B) by SMI diagnosis. BD, bipolar disorder; COPD, chronic obstructive pulmonary disease; CVA, cerebrovascular accident; SMI, severe mental illness; SSD, schizophrenia spectrum disorder.

Figure 2

Prevalence of the most prevalent physical health conditions across ethnicities within the SMI cohort and the SSD and BD subgroups. BD, bipolar disorder; COPD, chronic obstructive pulmonary disease; SMI, severe mental illness; SSD, schizophrenia spectrum disorder.

Figure 3

Visualisation of most prevalent comorbidities in individuals with SMI and comorbid diabetes. CKD, chronic kidney disease; COPD, chronic obstructive pulmonary disease; CVA, cerebrovascular accident; IBD, inflammatory bowel disease; MS, multiple sclerosis; SMI, severe mental illness; TIA, transient ischaemic attack.

Figure 4

Visualisation of most prevalent comorbidities in individuals with SMI and comorbid hypertension. CKD, chronic kidney disease; COPD, chronic obstructive pulmonary disease; CVA, cerebrovascular accident; IBD, inflammatory bowel disease; MS, multiple sclerosis; SMI, severe mental illness; TIA, transient ischaemic attack.

Figure 5

Visualisation of most prevalent comorbidities in individuals with SMI and comorbid asthma. CKD, chronic kidney disease; COPD, chronic obstructive pulmonary disease; CVA, cerebrovascular accident; IBD, inflammatory bowel disease; MS, multiple sclerosis; SMI, severe mental illness; TIA, transient ischaemic attack.