Section 3 -

Perivascular Dermatitis and Lichenoid Dermatitis Ronald P. Rapini University of Texas-Houston School of Medicine Houston, TX

Perivascular Dermatitis Numerous "rashes" belong here. We will primarily be discussing those cases with dermal perivascular inflammation without a lot of epidermal change, since Dr White will be covering psoriasiform dermatitis. Perivascular dermatitis is a term used when the dermal inflammatory cells (mostly lymphocytic, typically) are mainly around blood vessels. This is by far the most common pattern of inflammation in the dermis, because inflammatory cells initially come out of the blood vessels. It is useful to think of almost all inflammatory skin diseases as showing perivascular dermatitis, leaving the pathologist to remember only the exceptions. It is traditional to subdivide perivascular dermatitis into "superficial" and "superficial and deep" subtypes. This splitting is far less helpful toward making a specific diagnosis than is the clinical correlation, and the concomitant search for other findings, such as epidermal changes and inflammatory cell types. Other patterns, such as lichenoid and nodular may show areas of perivascular dermatitis, but when those patterns are found, the correct differential diagnosis is generally different. Splitting of categories into hybrids such as perivascular with interstitial dermatitis, perivascular and interface, perivascular with spongiotic, and perivascular with psoriasiform are of limited practical help. Perivascular dermatitis, superficial Morbilliform eruptions, especially viral eruptions, and drug eruptions Eczema Some erythemas, especially erythema multiforme Purpura pigmentosa chronica Perivascular dermatitis, superficial and deep Erythemas, especially gyrate erythemas such as erythema annulare centrifugum Eythema chronicum migrans Arthropod assaults Lupus erythematosus (also periadnexal) Polymorphous light eruption Syphilis, secondary Interface Dermatitis Interface dermatitis is dermatitis in which there is a degenerative change at the dermal-epidermal junction, with inflammation (mostly lymphocytes) mostly at the interface between the epidermis and dermis. Liquefaction degeneration, vacuolar alteration, and hydropic degeneration are three synonyms for this degenerative change that occurs at the basal layer. Tiny vacuolar spaces appear at the dermal-epidermal junction, often leaving the junction indistinct. This may result in formation of a subepidermal blister. The term lichenoid dermatitis overlaps with interface dermatitis, but "lichenoid" is used when there is a prominent band-like inflammatory infiltrate. Some authors divide interface dermatitis into the lichenoid type, and the vacuolar type, the latter having a less impressive inflammatory infiltrate. Lichen planus Lichen nitidus Mucha-Habermann disease Erythema dyschromicum perstans Erythema multiforme Lichenoid and fixed drug reaction Radiodermatitis Lichen sclerosus Rothmund-Thomson syndrome Bloom's syndrome Secondary syphilis (sometimes) Some viral exanthems Interface dermatitis of HIV infection Graft-versus-host disease Poikiloderma atrophicans vasculare Lupus erythematosus Dermatomyositis Lichenoid keratosis Mycosis fungoides Lymphomatoid papulosis Lichenoid Dermatitis Lichenoid is defined by the pathologist as a band-like infiltrate of inflammatory cells in the upper dermis, parallel to the epidermis. Liquefaction degeneration of the basal layer (interface dermatitis, colloid bodies, and melanin incontinence frequently occur together. The band of inflammatory cells is usually mostly lymphocytes, except there may be plasma cells (syphilis, mucous membranes, Zoon's balanitis), or eosinophils (lichenoid drug reaction). The clinician defines lichenoid differently to mean papules or plaques resembling lichen (symbiotic growth of algae and fungi) stuck on the skin. Some diseases that are lichenoid clinically are not lichenoid histologically (e.g., lichen simplex chronicus and lichen spinulosus). Lichen planus is both clinically lichenoid and pathologically lichenoid. Many of the diseases listed below that are histologically lichenoid are not clinically lichenoid. Pityriasis Lichenoides Lichen striatus (sometimes) Lichen planus Zoon's balanitis Keratosis lichenoides chronica Lichenoid drug eruption Lichenoid pigmentary purpura Lichen sclerosus Flegel's disease Syphilis, lichenoid secondary Graft-versus-host disease, chronic Poikiloderma atrophicans vasculare Lupus erythematosus Lichenoid keratosis Some neoplasms (Bowen's disease, melanoma, Spitz nevus, halo nevus, superficial basal cell carcinoma, etc). The neoplastic cells may be hiding in the band-like infiltrate! Mycosis fungoides Langerhans cell histiocytosis