As this study and our previous report [20
] have shown, the diagnosis of UPD and BPD based on a single interview is unstable over time, with 16.4% to 19.4% of subjects changing diagnosis, similar to the range of 11.7% to 19.7% reported in other studies [16
]. Using a diagnosis obtained at one year follow-up as 'gold standard' helps obtain a more reliable assessment.
Compared to the optimal cut-off of 7 reported by studies from western countries [5
] and Hong Kong [9
], this study showed a smaller optimal cut-off, which was similar to findings from Chinese mainland [23
]. This might partly due to the cultural differences, since Hong Kong is a very westernized city in China, which makes its culture and language greatly different from Chinese mainland.
In line with previous studies [5
], the MDQ is more sensitive in detecting BPDI than detecting BPDII. Although the originator of the MDQ did not specially access patients in remission from a mood episode, whether the patient's symptomatology at the time of screening will affect the MDQ performance is an interesting topic. A previous study with a small sample size [24
] showed the performance of MDQ was independent of depressive symptoms, but the relatively low test-retest reliability(kappa coefficient 0.64) with the whole sample implicated the possible influence of clinically relevant factors, such as the patient's mood state at time of completion. While compared to a report which sampled patients treated for depression [15
], the performance of the MDQ in detecting BPDII in this study was quite close (sensibility: 0.706 vs. 0.70), in spite of the different cut-off (7 vs. 4).
According to the initial conception of the MDQ's developers, a subject who will be screened positive has to meet the DSM-IV-TR criteria of manic or hypomanic episode, including symptom criteria and severity criteria. However, the poor performance of the section 2 and 3 in this study and other reports [6
] indicates an inadequacy in the original conception, especially when screening patients with BPDII. In this study, we went further by adding a question to ask subjects how long the positive symptoms lasted. We found that 16(32%) subjects with BPDII did not meet the DSM-IV-TR duration criteria of hypomanic episode (lasting at least 4 days). That means it is unrealistic to expect a self-rated questionnaire to help improve recognition of a past hypomanic episode among patients with BPDII.
However, MDQ without section 2 and 3 has been shown to be a valid screening tool for BPDII, and even for previously unrecognized bipolar disorder [25
]. One explanation for this might be that MDQ without section 2 and 3 helps recognize the opposite polarity-manic or hypomanic symptoms of BPDII, which helps improve the recognition of BPD [26
]. Recently, convergent evidence has shown that bipolarity is a sensitive and characteristic feature of BPD [26
]. For instance, a cross-sectional study [30
] found that clinically significant depressive symptoms occurred in 94.1% of those with (hypo) mania, while 70.1% in a depressive episode had clinically significant manic symptoms. In addition, both prospective [31
] and cross-sectional survey [32
] found that major depressive disorder (MDD) with subthreshold bipolarity shared similarities with BPD and more likely converted into BPD during follow-up. In this study, manic symptoms were also found to be more likely to occur in patients with BPD than those with UPD. In this context, it is not difficult to understand why MDQ without section 2 and 3 can be used as a screening tool to detect bipolar diathesis in depression [28
In summary, out study shows that the Chinese version of the MDQ without section 2 and 3 is a valid, brief and feasible tool for screening BPD from patients with a current depressive episode in Chinese mainland, although the psychometric properties in terms of internal consistency is not as excellent as reports in western countries [6
], which means some modification is needed. Furthermore, the small sample size in our study makes a larger prospective study necessary to further testify the validation of the Chinese version of MDQ under different clinical settings.