Overall incidence rates declined
“Over the study period, the suicide incidence rate for people with neurological disorders decreased from 78.6 per 100,000 person-years during the 1980-1999 years to 27.3 per 100,000 person-years during the 2000-2016 years,” wrote Dr. Erlangsen and colleagues. “The suicide incidence rate for those without a disorder decreased from 26.3 to 12.7 during the same time spans. ... The decline in the overall suicide rate over time did not affect the relative risk pattern.”
The decline in the general suicide rate in Denmark “has largely been attributed to means restriction, such as efforts to limit availability of firearms and particularly toxic medication,” the authors added.
In those time spans, the adjusted incidence rate ratio for suicide among those with dementia decreased from 2.4 to 1.0, and among those with multiple sclerosis from 2.0 to 1.0. “It is possible that the improvements observed for dementia and multiple sclerosis may be related to improvements in treatment and intensified community-based support,” Dr. Erlangsen and coauthors wrote.
When the researchers used people with rheumatoid arthritis as a reference group, those with a neurologic disorder had a higher suicide rate per 100,000 person-years, 30.2 versus 18.4. The adjusted incidence rate ratio for that comparison was 1.4.
In patients with Huntington’s disease, depression mediated by hyperactivity in the hypothalamic-pituitary-adrenal axis may contribute to the risk of suicide. “Witnessing the course of the disease in one’s parent” also may contribute the risk, the researchers wrote.
The analysis may have missed people with neurologic disorders diagnosed before 1977 if they did not have subsequent contact with a hospital, the investigators noted. In addition, diagnoses given in primary care were not included, suicide deaths may be underrecorded, and “adjusting for preexisting mental disorders could be viewed as overadjusting,” they wrote.
The study was supported by a grant from the Psychiatric Research Foundation in Denmark. The authors reported that they had no disclosures.
SOURCE: Erlangsen A et al. JAMA. 2020 Feb 4. doi: 10.1001/jama.2019.21834.