Fig.24.5 ).Ofinterest,theselesionsaresimilarinappearancetonormalvolar(palmsandsoles)skin,inwhichskinthickeningservesasanadaptationtorepetitivemechanicalstress.
The lesions often are raised, erythematous, and scaly and can be mistaken for keratinocytic neoplasms. Lichen simplex chronicus can be superimposed on and mask another (often pruritic) dermatosis. It is therefore important to rule out an underlying cause while recognizing that the lesion may be entirely trauma-related.
Fig. 24.5 Lichensimplexchronicus.Notethedistinctiveacanthosis,hyper-keratosis,andhypergranulosis.Superficialdermalfibrosisandvascularectasia,bothcommonfeatures,alsoarepresent.
ManyspecificinflammatorydermatosesexistandcanbemediatedbyIgEantibodies(urticaria),antigen-specificTcells(eczema,erythemamultiforme,andpsoriasis),ortrauma(lichensimplexchronicus).
Underlyinggeneticsusceptibilityplaysaroleinatopicdermatitisandpsoriasis.
Thesedisorderscanbegroupedbasedonpatternsofinflammation(e.g.,interfacedermatitisinlichenplanusanderythemamultiforme).
Clinicalcorrelationisessentialtodiagnosespecificskindiseases,sincemanyhaveoverlapping,nonspecifichistologicfeatures.
Numerous bacterial infections occur in skin. These range from superficial infections known as impetigo, to deeper dermal abscesses associated with puncture wounds that are caused by bacteria such as Pseudomonas aeruginosa. The pathogenesis is similar to that for microbial infections elsewhere (Chapter 9). Only impetigo is discussed here.
MORPHOLOGYImpetigoischaracterizedbyanaccumulationofneutrophilsbeneaththestratumcorneumthatoftenproducesasubcornealpustule.Nonspecificreactiveepidermalalternationandsuperficialdermalinflammationaccompanythesefindings.BacterialcocciinthesuperficialepidermiscanbedemonstratedbyGramstain.
Impetigo, one of the most common bacterial infections of the skin, is seen primarily in children. The causative organism is usually Staphylococcus aureus or, less commonly, Streptococcus pyogenes, and is typically acquired through direct contact with a source. Impetigo often begins as a single small macule, usually on the extremities or the face near the nose or the mouth, which rapidly evolves into a larger lesion (
Fig. 24.6 ), often with a honey-colored crust of dried serum. Individuals who are colonized by S. aureus or S. pyogenes (usually nasal or anal) are more likely to be affected. A less common bullous form of childhood impetigo may mimic an autoimmune blistering disorder.
Fungal infections are varied, ranging from superficial infections with Tinea or Candida spp. to life-threatening http://ebooksmedicine.net
Fig. 24.6 Impetigo.Achild’sarminvolvedbyasuperficialbacterialinfectionshowingthecharacteristicerythematousscablikelesionscrustedwithdriedserum.(Courtesy of Dr.Angela Wyatt,Bellaire,Texas.)
Aspergillus spp. infections in immunosuppressed individuals. Fungal infections can be superficial (stratum corneum, hair, and nails), deep (dermis or subcutis), or systemic, the last type arising through hematogenous spread, often in an immunocompromised patient.