Extra-anogenital bilharziasis cutanea tarda revisited.

Background: Even in schistosomiasis-endemic areas, extra-anogenital bilharziasis cutanea tarda (E-BCT) is rare. To date, the occurrence of E-BCT in pre-existing cutaneous pathology is undocumented. The study was undertaken to document the expanded clinicopathological spectrum and to comment on the putative pathogenetic mechanisms of a Schistosoma hematobium-associated E-BCT.

Methods: Eight-year clinicopathological appraisal of E-BCT.

Results: The clinical details are as follows. Seventeen specimens from 16 patients formed the study cohort. All specimens showed granulomatous inflammation with eosinophils, aggregates of terminal-spined S. hematobium ova and variable fibrosis. Copulating worms were identified in three biopsies. In 12/16 patients, E-BCT occurred in pre-existing pathology, including recurrent squamous papilloma (1), bilateral hidradenitis suppurativa (1) and scar tissue (10) with 7 showing a keloidal morphology. Prior and current urinary schistosomiasis was present in nine and seven patients, respectively.

Conclusion: E-BCT, a reflection of prior, re-infective or inadequately treated urinary schistosomiasis, is deemed to be a function of egg-laying consequent to the aberrant pathway of worms. Based on E-BCT occurrence in pre-existing extra-anogenital cutaneous fibroinflammatory and cicatricial processes and the presence of adult worms in three extra-anogenital biopsies in the present study, it is hypothesized that altered tissue mesenchymal repair reactions may promote extra-anogenital cutaneous worm entrapment and egg-laying.