MORPHOLOGYThehistologicappearancevariesdependingontheorganism,hostresponse,anddegreeofsuperinfection.Superficialinfectionsareoftenassociatedwithaneutrophilicinfiltrateintheepidermis.Deepfungalinfectionsproducegreatertissuedamageandoftenelicitagranulomatousresponse.Aspergillus canbeangioinvasive.Periodicacid–Schiff(PAS)andGomorimethenaminesilverstainsarehelpfulinidentifyingthefungalorganisms.
Superficial infections usually produce erythematous macules with superficial scale that can be pruritic, while deeper infections such as those seen with Aspergillus spp. are erythematous and often nodular and sometimes associated with local hemorrhage. Superficial fungal infections may have an annular appearance. However, they also may induce lesions that mimic other psoriasiform or eczematous dermatoses, so it is important to consider the possibility of fungal infection when these conditions are in the differential diagnosis.
Verrucae are proliferative lesions of squamous epithelial cells that are caused by human papillomavirus (HPV).
They are most common in children and adolescents, but may be encountered in any age group. HPV infection usually stems from direct contact with an infected individual or autoinoculation. Verrucae generally are self-limited, most often regressing spontaneously within 6 months to 2 years.
While some members of the HPV family are associated with preneoplastic and invasive cancers of the anogenital region (Chapters 6 and 18), cutaneous warts are mainly caused by low-risk HPV subtypes that lack transforming potential. Like high-risk HPV, low-risk viruses express viral E6 and E7 oncoproteins that lead to dysregulated epidermal cell growth and increased survival. Why low-risk viruses cause warts instead of cancer is likely due to structural variation in E6 and E7 proteins that affect their interactions with host proteins. Because the growth of warts is normally halted by the immune response, immunodeficiency is associated with more numerous and larger verrucae.
MORPHOLOGYDifferentkindsofwartsareidentifiedonthebasisoftheirgrossappearanceandlocationandgenerallyarecausedbydistinctHPVsubtypes.Verruca vulgaris (
Fig.24.7A ),themostcommontypeofwart,canoccuranywherebutisfoundmostfrequentlyonthehands,particularlyonthedorsalsurfacesandperiungualareas,whereitappearsasagray-whitetotan,flattoconvex,0.1-to1-cmpapulewitharough,pebblelikesurface.Verruca plana, orflat wart, iscommononthefaceordorsalsurfacesofthehands.Thesewartsareflat,smooth,tanmacules.Verruca plantaris andverruca palmaris occuronthesolesandpalms,respectively.Theserough,scalylesionscanreach1to2cmindiameterandmaycoalescetoformasurfacethatcanbeconfusedwithordinarycalluses.Condyloma acuminatum (venereal wart) occursonthepenis,femalegenitalia,urethra,andperianalareas(Chapters18and19).Histologicfeaturescommontoverrucaeincludeepidermal hyperplasia, whichisoftenundulantincharacter(so-calledverrucous orpapillomatous epidermal hyperplasia)(
Fig.24.7B ,top panel),andcytoplasmicvacuolization(koilocytosis), whichpreferentiallyinvolvesthemoresuperficialepidermallayers,producinghalosofpallorsurroundinginfectednuclei.Infectedcellsalsomaydemonstrateprominentkeratohyalingranulesandjaggedeosinophilicintracytoplasmicproteinaggregatesasaresultofimpairedmaturation(
Fig.24.7B , bottom panel).