The words “bipolar” and “disorder” are just words. Sometimes I capitalize them and sometimes I don’t. I haven’t yet found any definitive text which seems to care, so I don’t really care either. Usually, I won’t capitalize them because that means a little less typing for me.
In general, you can consider the following variations of the phrase equally valid in any circumstance:
- Bipolar Disorder (with initial capitalization).
- BiPolar Disorder (with camel-case-like capitalization; the “b” and “p” of bipolar are capitalized, as is the “d” of disorder).
- bipolar disorder (no capitalization)