A range of case studies [17–20], single case experimental
design series [21, 22] and open trials [23, 24],
have reported CBT results in decreases in depression
and anxiety in PD patients. However it is difficult to
generalize from these studies with small sample sizes
and lack of control groups. There have only been two
randomized controlled trials (RCTs) to date examining
the impact of CBT on depression in PD. In the largest
study to date 80 participants with PD and depression
were randomized to receive 10 sessions of individual
CBT plus clinical monitoring (CM) compared to
clinical monitoring only [26]. CBT participants had
significantly greater reductions in HAM-D depression
scores, and there were significantly more treatment
responders in the CBT+CM group compared to the
CM group (56% versus 8%). Gains were maintained
at one-month follow-up. In a recent RCT [27] of group
CBT a waitlist-controlled design was used with 18
adults with PD and a diagnosis of depression and/oranxiety. In the second study, participants were randomized
to either an 8 week CBT group or 8 week waitlist
consisting of clinical monitoring preceding treatment.
At post-treatment CBT participants reported greater
reductions in depression than waitlist participants of a
large effect (d = 1.12). Large secondary effects on anxiety
were also observed for CBT participants (d = 0.89).
Treatment gains were maintained and further improved
during follow-up, where at 6-month follow-up, significant
and large effects were observed in the CBT group
for both depression (d = 2.07) and anxiety (d = 2.26). It
is particularly noteworthy that these very large effect
sizes of greater than 2.0 at 6 month follow-up indicate
not only the durability of effects of group CBT on
depression and anxiety, but also that treatment gains
are furthered over time. These studies are encouraging
given the large effect sizes found particularly in
reduction of depression in PD, however more research
is still required with RCTs with adequate sample sizes
and longer follow up periods.