Many neurological conditions are more frequent among individuals with severe mental illness

An analysis of data on individuals with severe mental illness available in the UK Clinical Practice Research Datalink found that 13 of the 15 groups of neurological conditions considered were more prominent among people with severe mental illness than in individuals without severe mental illness at the time of their psychiatric diagnosis. Most notably, the odds of dementia and Parkinson’s disease were around 4 times higher, while the odds of having epilepsy were 3 times higher 5 years after the diagnosis of severe mental illness. The paper was published in BMJ Mental Health.

Studies indicate that individuals suffering from serious psychiatric disorders such as schizophrenia, bipolar affective disorder, and other psychotic conditions have an increased likelihood of suffering from various adverse physical medical conditions. For example, these individuals have elevated rates of cardiovascular, endocrine, pulmonary, and gastrointestinal diseases, with cardiometabolic disorders receiving the most research attention.

However, the relationship between psychiatric and neurological conditions is not fully understood. Neurological conditions are disorders that affect the brain, spinal cord, or peripheral nerves, leading to impairments in movement, sensation, cognition, or autonomic functioning.

Examples include Parkinson’s disease, epilepsy, multiple sclerosis, stroke, dementia, and various neuropathies, which can vary widely in cause, course, and severity. Researchers increasingly believe that many of these conditions are actually neuropsychiatric in nature. There are studies indicating that these conditions might actually develop more frequently in individuals with severe mental illness.

Study author Ella Burchill and her colleagues wanted to explore the frequency with which various neurological conditions occur in individuals with severe mental illnesses from 5 years before their mental illness is diagnosed to 5 years after the diagnosis.

While the exact causal relationship remains unclear, the authors note four possibilities for this overlap: severe mental illness and neurological conditions may share a common genetic or developmental cause; psychiatric symptoms might act as an early “prodrome” preceding the full onset of a neurological condition; severe mental illness or its treatments (such as antipsychotic medications) might cause neurological issues; or early-life neurological conditions might disrupt brain development and subsequently cause mental illness.

The authors identified individuals with severe mental illness from the primary care database Clinical Practice Research Datalink (CPRD). This database is broadly representative of the UK population, containing data from approximately 24% of UK residents. This study included individuals aged 18 to 100 who first received a diagnosis of schizophrenia, bipolar disorder, or other psychosis between 2000 and 2018.

Study authors matched each of these patients with up to four individuals without severe mental illness from the same primary care practices. In total, the analysis included 68,789 individuals with severe mental illness and 274,827 individuals without severe mental illness. Study authors looked into diagnoses of 15 groups of neurological conditions at seven distinct time points: 5, 3, and 1 year prior to the diagnosis of severe mental illness; exactly at the time of the severe mental illness diagnosis; and 1, 3, and 5 years after the diagnosis.

The 15 groups of neurological conditions study authors considered were: multiple sclerosis (or other white matter disorders), cerebrovascular disease, dementia (inclusive of Alzheimer’s, Lewy body, vascular, human prion disorders), ataxic disorders, epilepsy (or seizures), Parkinson’s disease, parkinsonism other (secondary/ drug induced), paralysis, movement disorders other (choreiform, movement, dystonic), structural developmental anomalies or disorders of cerebrospinal fluid (CSF) pressure or flow, cerebral palsy, spinal cord disorders, disorders of nerve root, plexus or peripheral nerves, motor neuron diseases or related disorders, and disorders of autonomic nervous system.

The results showed that, at the time of first receiving a severe mental illness diagnosis, the five most common neurological conditions were epilepsy (3.71%), cerebrovascular disease (3.02%), dementia (1.65%), Parkinson’s disease (0.68%) and multiple sclerosis (0.32%). Thirteen groups of neurological conditions were more prevalent among participants with severe mental illness compared to the control group (individuals without severe mental illness) at the time of diagnosis of severe mental illness. Eleven were more prevalent at all time points, including times before the diagnosis.

At the time of the diagnosis, the most elevated odds for individuals with severe mental illness were for “other parkinsonism” (a category that includes secondary or drug-induced tremors, which was 8.3 times higher compared to the control group), and other movement disorders (3 times higher). At 5 years after the diagnoses, the odds of suffering from dementia and Parkinson’s disease were roughly 4 times higher, and the odds of having epilepsy were 3 times higher than in the control group.

Importantly, the researchers found significant differences based on the specific type of mental illness. While individuals with bipolar disorder and other psychoses had elevated rates for almost all neurological conditions, those with schizophrenia had rates closer to the general population for many conditions. The authors suggest this could be due to “diagnostic overshadowing”—a phenomenon where doctors mistakenly attribute a patient’s genuine physical or neurological symptoms to their pre-existing schizophrenia, leading to delayed or missed diagnoses.

“Many neurological conditions have higher prevalence in the SMI [severe mental illness] cohort compared with those without SMI,” the study authors concluded.

The study contributes to the scientific understanding of the relationships between psychotic and neurological disorders. However, it should be noted that the observational design of this study does not allow strict causal inferences to be derived from the results.

The paper, “Temporal relationship between severe mental illness and neurological conditions in a UK primary care cohort,” was authored by Ella Burchill, Jonathan P. Rogers, David P. J. Osborn, Glyn Lewis, Anthony S. David, Joseph F. Hayes, and Naomi Launders.