Extensive fibrin accumulation and accompanying epithelial changes in the pathogenesis of ligneous mucosal disease (ligneous periodontitis).

Certain abnormal products of human tissues are resistant to degradation. The fibrillary ultrastructure of some of these are seen integrated with normal tissue components. The accumulations seen in colloid milium, lichen, and macular amyloidosis are of this type. Apoptosis of keratinocytes and filamentous degeneration of some proteins can be important in the pathogenesis. A similar pathogenetic mechanism is possible in ligneous mucosal disease, which is a rare disorder of plasminogen deficiency characterized by amyloid-like amorphous accumulations. Gingival and conjunctival mucosal pseudomembraneous masses are typical and concomitant involvement of other sites are not unusual. The accumulated substance is thought to be an abnormal fibrin degradation product. In this study, we have examined 6 representative samples from 5 gingival and 1 conjunctival lesions displaying characteristic features. Immunohistochemically, fibrinogen was detected as an early change. TUNEL staining revealed numerous apoptotic keratinocytes in this phase as well. These cells also expressed nuclear factor kappa beta. Apoptotic cells showed loss of epithelial cadherin immunostaining. In the later phase, the subepithelial accumulations failed to stain with antifibrinogen, wide spectrum, and high molecular keratins, type 4 collagen and nuclear factor kappa beta. Our findings suggest that the accumulations in ligneous mucosal disorder result from an abnormal healing process and they probably form as a combination of organised fibrinogen, epithelial fragments, and connective tissue matrix.