Changes in Treated Incidence of Borderline Personality Disorder in Denmark: 1970-2009

Objectives: To investigate whether there are any trends in treated incidence of borderline personality disorder (BPD) in Danish psychiatric hospitals based on different diagnostic systems from 1970 to 2009. Methods: All patients diagnosed with BPD for the first time as a main or an auxiliary diagnosis treated in in- or outpatient facilities in Danish psychiatric hospitals were identified through the Danish Psychiatric Central Research Register. Age-standardized, sex-specific, and standardized rates were calculated for the International Classification of Diseases (ICD), Eighth Revision, diagnostic period from 1970 to 1993 and the ICD-10 diagnostic period from 1994 to 2009. Results: The incidence for BPD in females as a main or an auxiliary diagnosis increased linearly from 1970 to 2009 (beta = 0.69 per 100 000 per year [95% CI 0.66 to 0.73]). The rates for males also increased linearly from 1970 to 1993 (beta = 0.37 [95% CI 0.30 to 0.43]) followed by a linearly decrease (beta = -0.22 [95% CI -0.29 to -0.15]) in the ICD-10 period from 1994 to 2009. The increase in females with BPD after the mid-1990s is smaller when controlling for outpatients mandatorily registered from 1995. Conclusion: The lack of defined criteria for BPD in ICD-8 may have been interpreted broadly to mean Kemberg's overarching concept of borderline personality organization, resulting in similar rates for males and females. However, in ICD-10, clinicians using the more narrow criteria for emotionally unstable personality disorder (borderline type), tended to diagnose BPD more commonly in women. These results suggest the importance of using specific criteria in diagnosing. They also suggest the importance of stability in the diagnostic criteria for BPD and other disorders.