점막의 미세한 변화만 발생하여 정상 점막과 구분되지 않고 조직 생검으로만 진단된 경우들도 보고되고 있다.
There have also been reports of cases in which only minor changes in mucous membranes occurred and were not distinguished from normal mucous membranes and were diagnosed only by tissue biopsy.