Elaine, Clemson lost the big game so everyone is back to work. The Clemson boffin thought it was scarring but he sent it off to a CM boffin in FL who agreed it is scarring. I don't get it myself and will send a sample off to the clinic. This is the response, Gary is the guy from FL.
"Just heard back from Gary. He has seen it before, and agrees with my guess that it might be some kind of scars or scarring response. From the pictures, the crape myrtle seems to suffer from some previous wound that healed over, and the 'bumps' are associated with the wound. I don't think it is diseased. Of course, a sample could always be sent to the Plant Problem Clinic for diagnosis.
If the crape myrtles are not declining, I would leave them be but keep an eye on them."