Temporal relationship between severe mental illness and neurological conditions in a UK primary care cohort

A higher prevalence of neurological conditions has been found in schizophrenia, bipolar disorder and other psychotic illnesses compared to the general population. We aimed to understand the cumulative prevalence of 15 neurological conditions in people with severe mental illness (SMI) from 5 years before to 5 years after their SMI diagnosis.

We identified patients with SMI, aged 18-100 years from 1 Jan 2000 to 31 Dec 2018, from the UK Clinical Practice Research Datalink. Each SMI patient was matched 1:4 to individuals without SMI. The cumulative prevalence of 15 neurological conditions was recorded at 5, 3 and 1 years prior to SMI diagnosis; at SMI diagnosis; and 1, 3 and 5 years after SMI diagnosis. Prevalences were compared with logistic regression.

We identified 68 789 patients with SMI and 274 827 comparators. Of 15 neurological conditions, 13 (multiple sclerosis, cerebrovascular disease, dementia, ataxic disorders, epilepsy, Parkinson's disease, other parkinsonism, paralysis, other movement disorders, cerebrospinal fluid disorders, cerebral palsy, disorders of nerve root, plexus or peripheral nerves and autonomic disorders) were more prevalent in SMI compared with comparators at the time of SMI diagnosis. Dementia (OR: 4.22; 95% CI 3.88 to 4.58), epilepsy (OR: 3.01; 95% CI 2.83 to 3.19) and Parkinson's disease (OR: 3.97; 95% CI 3.45 to 4.57) were particularly elevated at 5 years post-SMI diagnosis.

Many neurological conditions have higher prevalence in the SMI cohort compared with those without SMI. The different prevalence patterns observed in our study highlight the need to establish the causal pathways between specific SMI and neurological disease diagnoses.