Pseudoxanthoma elasticum Key Features Curled and frayed, calcified elastic fibers in the reticular dermis (pink or blue squiggles) Elastic tissue (Verhoeff–Van Gieson) and calcium (Von Kossa) stains highlight the distorted elastic fibers Pseudoxanthoma elasticum is an autosomal-recessive and, less commonly,…
Leukocytoclastic vasculitis (LCV) Key Features Perivascular infiltrate with neutrophils Karyorrhexis (nuclear dust, leukocytoclasis) Expansion of the vessel wall Fibrin deposition within the vessel wall Erythrocyte extravasation Clinical lesions of leukocytoclastic vasculitis are purpuric and often palpable. Vasculitis involving arterioles commonly…
Granulomas are discrete collections of histiocytes with or without multinucleate giant cells. Histiocytes are bone marrow derived or mesenchymal. In granulomas, their cytoplasmic membranes touch with no intervening connective tissue. Infectious etiologies, especially fungal and mycobacterial, should be excluded with…
Subcorneal vesiculobullous disorders Pemphigus foliaceus Key Features Subcorneal split Acantholysis (loss of attachments between keratinocytes) Dyskeratosis may occur within the granular layer Direct immunofluorescence demonstrates “netlike” deposition of immunoglobulin (Ig) G and C3 between keratinocytes in upper epidermis Pemphigus foliaceus…
Psoriasis Key Features Neutrophils above parakeratosis in stratum corneum Little to no serum in stratum corneum Alternating neutrophils and parakeratosis in the stratum corneum (sandwich sign) Neutrophilic spongiform pustules Little spongiosis in adjacent epidermis Tortuous blood vessels in dermal papillae…
Lichenoid interface dermatitis Key Features Basal layer is destroyed Civatte bodies Sawtooth rete pattern Causes of lichenoid interface dermatitis Lichen planus Benign lichenoid keratosis (BLK, lichen planus–like keratosis) Lichenoid drug eruption Lichenoid graft-versus-host disease (GvHD) Hypertrophic lupus erythematosus Lichenoid regression…
Solar lentigo Key Features Thin rete with bulbous tips “dipped in chocolate” Differential Diagnosis Reticulated seborrheic keratosis looks similar to a lentigo but with anastomosis of rete and horn cysts. Melanotic macule Key Features Common on the lips and genitalia…
Blue sweat gland tumors differentiate toward the secretory portion of the sweat gland. Red sweat gland tumors differentiate toward the sweat duct. Sweat duct tumors often demonstrate clear cell change. Most sweat gland tumors can show at least focal decapitation…
Pilar neoplasms Pilar neoplasms differentiate toward (resemble) various parts of the normal hair follicle. They are named according to what they resemble. Before reading this chapter, review the discussion of hair anatomy in Chapter 1 . Blue pilar tumors differentiate…
Actinic keratosis Key Features Crowding, disorder, and atypia of epidermal keratinocytes Arises from the basal layer Solar elastosis typically present Atypical cells commonly surround the follicular infundibulum. In two-dimensional sections, they appear to form a shoulder zone peripheral to the…