A large retrospective study supports the notion that depression may be an independent risk factor for Parkinson’s disease (PD).
Patients with depression were about threefold more likely to develop PD than matched patients without depression, report Albert Yang (National Yang-Ming University, Taipei, Taiwan) and team. And the association persisted after they excluded patients who were diagnosed with PD within 5 years of receiving a diagnosis of depression, suggesting that depression was not simply a very early manifestation of PD.
“However, neurodegenerative disorders such as PD may initiate 10 to 20 years before they become symptomatic, and depression in PD may have some unusual characteristics that make the diagnosis of depression in PD very difficult,” they write in Neurology.
“[T]herefore, we cannot obviate the possibility that depression is also an early symptom of PD from our study results.”
During 10 years of follow-up, 1.42% of 4636 patients with depression, identified in a national database, were diagnosed with PD. This was a significantly higher proportion than the 0.52% of 18,544 age- and gender-matched patients without depression, and equated to a 3.24-fold increased risk after accounting for age and gender.
The elevated risk persisted after excluding patients diagnosed with PD within 2 years of developing depression, at a 3.10-fold increase, and within 5 years, at a still significant 2.84-fold increase.
As expected, PD risk among patients with depression increased with older age after accounting for confounders; it was 10-fold higher among those aged at least 65 years than among younger patients.
Antidepressant treatment itself was not an independent predictor for PD risk, the team notes. However, PD risk was 2.18-fold higher among patients with depression that was difficult to treat than among those with treatable depression. The researchers defined the latter as having antidepressants altered at least twice within the first 2 years after diagnosis, with each having been trialed for at least 60 days.
The risk associated with treatment-resistant depression “may imply that neurotoxicity of depression is related to the severity or resistance of depression, and the more resistance of depression, the more risk of PD in these patients,” say Yang and team.
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