Does fibroids cause brown spotting instead of a regular period?

Yes they can: Fibroids are benign (non cancerous) tumors of the uterus that are associated with painful, heavy periods. Depending on their location, they can certainly cause bleeding unrelated to your cycle. They can be treated with medications that are hormonal or non-hormonal, and they are also commonly treated surgically by removing the fibroid (s) or the entire uterus.