Could Beta Blocker Trigger Vitiligo?

My 10 year old son has just been diagnosed with Vitiligo. He began taking Atenolol for treatment of migraines last May. Last summer I noticed he had a large lesion on one knee that had lost pigment. This year the same is happening to his other knee. Could the beta blocker have triggered Vitiligo? I have found literature that Vitiligo patients should avoid beta blockers. We plan to stop the Atenolol. Thanks for your response.