Cal. Lab. Code § 4067
If the jurisdiction of the appeals board is invoked pursuant to Section 5803 upon the grounds that the effects of the injury have recurred, increased, diminished, or terminated, a formal medical evaluation shall be obtained pursuant to this article.
When an agreed medical evaluator or a qualified medical evaluator selected by an unrepresented employee from a three-member panel has previously made a formal medical evaluation of the same or similar issues, the subsequent or additional formal medical evaluation shall be conducted by the same agreed medical evaluator or qualified medical evaluator, unless the workers' compensation judge has made a finding that he or she did not rely on the prior evaluator's formal medical evaluation, any party contested the original medical evaluation by filing an application for adjudication, the unrepresented employee hired an attorney and selected a qualified medical evaluator to conduct another evaluation pursuant to subdivision (b) of Section 4064, or the prior evaluator is no longer qualified or readily available to prepare a formal medical evaluation, in which case Sections 4061 or 4062, as the case may be, shall apply as if there had been no prior formal medical evaluation.
Ca. Lab. Code § 4067