Has he had his vitamin D level checked? The reason I ask is because the physical therapist my husband saw for the vertigo issue mentioned that it could be caused by a vitamin D deficiency. MSK's blood work did not include checking vitamin D level, so he had his primary care doctor order it and it was severely low, like practically non existent! He started taking a vitamin D supplement and did not have any more vertigo issues. It might be worth looking into. I hope he gets some relief soon.