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INCONTINENTIA PIGMENTI
In the section on lichenoid reactions, one of the basic reaction patterns was characterized as erythema multiforme-like. A common feature of this type of lichenoid
reaction is the clustering of necrotic keratinocytes in lytic defects in a damaged basal unit of the epidermis. The dead keratinocytes tend to cluster in the viable portion of the epidermis; viable keratinocytes
tend to form whorls about the clusters of dead keratinocytes. In the transfer of cells from the basal unit to the superficial unit, the clusters of necrotic cells and the whorls of viable keratinocytes are included.
The clusters are carried to the surface; they are discharged into the keratinized debris. This movement of dead and viable cells in groups has been characterized as whorled transepidermal elimination. The reaction
is basic to erythema multiforme but is seen in other diseases, such as lichenoid fixed drug eruption. It is also a feature of the reaction in incontinentia pigmenti, but is variably represented, depending on
the age of the affected patient and the stage of the disease.
In the inflammatory phase of incontinentia pigmenti, the epidermis shows hyperplasia of the superficial unit and liquefaction degeneration of the basal layer of the
epidermis. Lytic defects, some of which contain clusters of necrotic keratinocytes, form at the dermal-epidermal interface. Epidermal defects are a feature; they may be manifested in vesicular patterns. The vesicles
tend to have a reticulated quality (S7C7P4-2-3). Necrotic keratinocytes appear first at the dermal-epidermal interface and in the basal unit of the
epidermis. They are carried upward (S7C7P4-1). Patterns of whorled transepidermal elimination are common (S7C6P3-1-3). Inflammatory infiltrates are perivascular in the reticular dermis and band-like in the papillary dermis. Eosinophils
are a common component of the infiltrates (S7C6P3-5). Migratory histiocytes are a prominent feature of the infiltrates at the
dermal-epidermal interface and in the defects among keratinocytes (S7C6P3-3). Melanophages are present in the dermal infiltrates.
At a later stage in the evolution of the process, the inflammatory changes and the cytopathic phenomena are less prominent.The epidermis is hyperplastic in verrucous
patterns; it shows scattered, necrotic keratinocytes and loose infiltrates of eosinophils (S7C6P3-4).
Berlin AL, Paller AS, Chan LS: Incontinentia pigmenti: a review and update on the molecular basis of pathophysiology. J Am Acad Dermatol 2002; 47: 169-87.
VESICULAR PEMPHIGUS
A variant of pemphigus is characterized by small vesicular lesions (i.e., vesicular pemphigus) (S7C8P5-1 & 2).
The epidermis is hyperplastic. Rounded defects form in the basal unit with a single row of basal keratinocytes outlining the defect along its floor. As the defect
enlarges, it compresses the epidermis forming the roof of the defect (S7C8P5-3 & 4). Eventually, multiple,
individually isolated vesicles are spaced in the epidermis in the affected areas. The vesicles contain fibrin, rounded (acantholytic), necrotic keratinocytes, and a sprinkling of inflammatory cells (S7C8P5-5). The keratin layer is not significantly affected.
Perivascular infiltrates are composed of lymphocytes and histiocytes (S7C8P5-6). Eosinophils are a part of the interstitial infiltrates of both
the dermis and the epidermis (including the vesicles) (S7C8P5-3). In part, the patterns qualify as eosinophilic
spongiosis, but histologic patterns take on specificity with the demonstration of inter-cellular antibodies of pemphigus type.
The papillary dermis is edematous.
NEUTROPHILIC PEMPHIGUS
In some examples of pemphigus, a separation occurs at the interface between the superficial and the basal units of the epidermis (S7C9P6-1 & 2).
In addition, neutrophils, along with histiocytes, collect in linear arrays at this interface in anticipation of a separation (S7C9P6-3-5,
& S7C10P7-2-5). The patterns are distinct from the usual examples of either pemphigus vulgaris or pemphigus foliaceus (S7C11P8-1 & 2). Lesions showing these variant patterns may be related to vesicular pemphigus (S7C10P7-1); like vesicular pemphigus, some of the lesions are more pustular than vesicular (S7C10P7-4).
Prost C, et al: IgA autoantibodies bind to pemphigus vulgaris antigen in a case of intraepidermal neutrophilic IgA dermatosis. J Am Acad Dermatol 1991;25: 846-8.
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