homojabi:

BPD stands for borderline personality disorder and BD stands for bipolar disorder. The two are often confused and used in place of the other because there is a lot of symptom overlap, misdiagnosis and comorbidity between the two. Also, due to the stigma of BPD, someone with BPD might be diangosed with BD instead. Approximately 40% of people with one of the disorders has both (this was orignally thought to be less than 20%). 

Here are three (3) ways commonly used to differetniate the two:

1. People with BPD cycle much more quickly, often several times a day (shifts can even last minutes/seconds).
   
2. The moods in people with BPD are more dependent, either positively or negatively, on what’s going on in their life at the moment. Anything that might smack of abandonment (however far fetched) is a major trigger.
   
3. In people with BPD, the mood swings are more distinct. People with bipolar disorder swing between all-encompassing periods of mania and major depression, while the mood swings typical in BPD are more specific.
   

Here is a more encompassing post explaining the differences. 

Having a dual-diagnosis is usually associated with a greater risk of suicide. Besides that impulsivity, mood instability, inappropriate anger, suicidal behavior, and unstable relationships are shared with bipolar disorder.

This article goes into the similarities, differences and reasons for misdiagnosis in a much more detailed manner. 

Treatment for a dual diagnosis includes medication, therapy and DBT (and by themselves they are often treated similarly), but in the comorbid situation both disorders need to be addressed, which is what makes misdiagnosis such a dangerous thing. 

Resources for Bipolar Disorder: one (1), two (2), actuallybipolar

Resources for BPD: one (1), two (2), actuallybpd, actuallyborderline