The question of how frequently depression occurs in persons with PD is a striking example of how even ostensibly simple questions can be hard to answer when it comes to understanding depression in PD. Reported rates of depression have varied enormously from study to study. An overall depression rate of 43% is one of the most commonly cited figures.1 However, this figure includes persons with major depressive disorder and minor depression or dysthymia. Another confounding factor with this estimate is the population being studied. Studies that have reported high rates generally used specialty populations, in contrast to the lower rates generally seen in community-based samples.
As part of a wider prevalence study of PD, Tandberg et al.2 carefully assessed depressive symptoms in PD patients. They found that 7.7% of community dwelling patients met DSM-III criteria3 for major depressive disorder (MDD). Additionally, they used the Montgomery-Asberg depression rating scale (MADRS)4 to obtain information on depressive symptoms. According to the MADRS, only 5.1% of patients were moderately to severely depressed, but another 45.5% had mild depressive symptoms. The rate of major depression was also strongly affected by cognitive impairment as defined by MMSE score.5 Rates of MDD were 3.6% in patients with an MMSE > 20 but increased to 25.6% in patients whose MMSE was below 20. Interestingly, rates were also higher in those with possible PD (18.8%) vs. those with probable PD (4.6%). The authors attribute these figures to a higher rate of dementia in those with possible PD and suggest that the higher rates in the cognitively impaired indicate more widespread cerebral involvement.2
Another study demonstrating relatively low rates of MDD used structured interviews to evaluate all cogni-tively intact PD patients in the community who reported depressive symptoms on the General Health Questionnaire (GHQ).6,7 While depressive symptoms on the GHQ were reported in 34.2% of PD patients, only 2.7% met criteria for MDD.
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