Strengths, limitations and interpretation
In addition to earlier published reviews concerning the association
between endometriosis and psychological problems [21,96], the
current review specifically provides an up to date overview with regard
to both depressive and anxiety symptoms in these patients. Furthermore,
we provided information concerning factors that correlate with
depression and anxiety symptoms in endometriosis. Reporting of these
correlations is important to recognise vulnerable patients in clinical
practice. As research demonstrated the reliability of non-surgical
diagnosis of endometriosis, we also included studies including patients
with a clinical diagnosis of endometriosis, which made it possible to
generate a large number of studies. In contrast to Gambadauro et al, our
review excluded studies with self-reported diagnoses of depression and
studies using non standardized assessment methods, to limit the risk of
over-reporting. The meta-analysis included solely studies using a
standardized outcome measure to limit heterogeneity in the results. The
overall SMD of studies comparing endometriosis patients with CPP
patients without endometriosis showed an I-squared of 0% (p=0.798) for
depression scores and an I-squared of 33.2% (p=0.134) for anxiety
scores, which means that the heterogeneity between these studies was
low. Nevertheless, heterogeneity between studies comparing endometriosis
patients with healthy controls was relatively high: I-squared 84.6%
(p<0.001) for depression scores and I-squared 68.1%
(p<0.001) for anxiety scores. This makes it difficult to
compare and generalize the study outcomes. Hence, strategies of research
groups and their assessment tools need to be standardized to produce
robust and reliable results for meta-analyses. However, a sub-analysis
including only studies using the HADS as outcome measures, did not
change outcome nor improved I-squared results, meaning that
heterogeneity was probably caused by differences in demographic or other
factors. Furthermore, this review has some other limitations. First,
including articles in English only limits the number of included
studies. Risks of bias were mostly caused by study design and patient
selection as most studies included women in tertiary referral centres.
This could have led to an over-presentation of symptoms compared to
patients in the general population. Although validated, the used
assessment tools are predominantly self-assessment questionnaires, which
gives an indication of a depressive or anxious state but does not
provide a valid diagnosis. Studies using reported ICD-9 diagnoses given
by professionals could have led to under-reporting of depression and
anxiety complaints as those might have not received an official
diagnosis. Another important limitation is the variation in types of
anxiety disorders that were pooled in the meta-analysis. Screening tools
for anxiety disorders usually provide lower sensitivity and specificity
than tools for depressive disorders, as anxiety disorders have more
heterogeneous symptoms (state, trait or phobic anxiety) [94].