There is a link between schizophrenia and bipolar (schizoaffective disorder), and schizophrenia and SPD are in the same family. But, I don't think there is a link between SPD and bipolar, at least from what I've gathered online and in forums. It seems pretty uncommon to be diagnosed with both, however, I have seen several people say they exhibit schizoid traits during depressive episodes. If you want to get some insight from pwSPD there is a fairly active forum at psychforums.com.