Atopic dermatitis with increased severity along a line of Blaschko

Superimposed type 2 segmental atopic dermatitis: a case series and review of the literature

Generalized acquired dermatoses can seldom manifest more prominently or exclusively along the lines of Blaschko. Six individuals with segmental atopic dermatitis (AD) have been reported to date. We present three additional cases of segmental cutaneous manifestations superimposed on generalized AD, and review the relevant literature.

A Case of Linear Exacerbation of Atopic Dermatitis with Secondary Prurigo Nodularis

Inflammatory acquired Blaschko-linear dermatoses (IABLD) are a continuous concept involving diseases such as lichen striatus, blaschkitis, and atopic dermatitis. However, atopic dermatitis that showed increase in severity along Blaschko lines is rarely reported on its own. Herein, we report a rare case of atopic dermatitis with secondary prurigo nodularis along Blaschko lines, which may be valuable in broadening the concept of IABLD. A 28-year-old male presented with multiple, pruritic, brownish nodules on the left lower extremity along Blaschko lines for 3 to 4 years. The patient had atopic dermatitis since childhood. Histopathologic findings revealed compact orthohyperkeratosis, hypergranulosis, spongiosis, and irregular acanthosis in the epidermis. Fibrosis with vertically arranged collagen fibers and perivascular lymphohistiocytic infiltration were shown in the upper dermis. We diagnosed the case as secondary prurigo nodularis along Blaschko lines, accompanied by the preceding atopic dermatitis. We hypothesized that the patient’s underlying atopic dermatitis increased in severity along Blaschko lines, and prurigo nodularis occurred due to frequent scratching. The lesions improved with topical methylprednisolone cream, oral antihistamines and intralesional triamcinolone injection.

Superimposed linear atopic dermatitis treated with dupilumab

Common polygenic skin disorders, such as atopic dermatitis, may rarely present in a segmental or linear distribution due to cutaneous mosaicism. Only seven cases of superimposed linear atopic dermatitis have been reported to date. Here, we present a child with severe superimposed linear atopic dermatitis and highlight the first successful use of dupilumab in its treatment.

Mosaicism in genodermatoses

Genodermatoses are inherited disorders presenting with cutaneous manifestations with or without the involvement of other systems. The majority of these disorders, particularly in cases that present with a cutaneous patterning, may be explained in the context of genetic mosaicism. Despite the barriers to the genetic analysis of mosaic disorders, next-generation sequencing has led to a substantial progress in understanding their pathogenesis, which has significant implications for the clinical management and genetic counseling. Advances in paired and deep sequencing technologies in particular have made the study of mosaic disorders more feasible. In this review, we provide an overview of genetic mosaicism as well as mosaic cutaneous disorders and the techniques required to study them.

A linear lesion in a child with atopic dermatitis: Not a coincidence

A blaschkolinear lesion in a patient with atopic dermatitis can be a superimposed segmental manifestation of this polygenic disorder. Knowledge of this phenomenon, presence of less severe, disseminated, symmetrically distributed lesions of the same disorder and, if necessary, histology are helpful in the differential diagnosis from other linear inflammatory diseases.

Superimposed linear atopic dermatitis

Superimposed linear atopic dermatitis is rarely manifested in polygenic disease as a counterpart to type 2 segmental mosaicism of monogenic skin diseases. Linear arrangement following Blaschko lines represents more severe disease on a generalized background of atopic dermatitis, perhaps reflecting clonal loss of heterozygosity. Only three cases of superimposed linear atopic dermatitis have been reported; we describe three additional cases.

Patterned disorders in dermatology

The skin gives us an opportunity to study pathologies unapparent in other systems such as patterned disorders. Among the best-identified patterns of skin disorders are the well-known lines of Blaschko, but other types of skin-patterned lesions have also been recognized. This short review will describe and discuss these different patterns and their pathophysiologic mechanisms, such as somatic mosaicism and X-chromosome associated mosaicism. Cutaneous patterned disorders are thought to be associated usually with inherited diseases per se, but in fact they are also reported in so-called acquired diseases. These cases suggest the existence of an underlying defect in a gene closely associated with the disease pathogenesis. The study of these acquired patterned disorders in the future may help us to understand the biologic foundations and pathogenesis of common human diseases.

Atopic eczema and the filaggrin story

The discovery that null mutations in the filaggrin gene (FLG) are associated with atopic eczema represents the single most significant breakthrough in understanding the genetic basis of this complex disorder. The association has been replicated in multiple independent studies during the past 2 years with the use of various methodologies, from populations in Europe, the United States, and Japan. Filaggrin plays a key role in epidermal barrier function, and its association with atopic eczema emphasizes the importance of barrier dysfunction in eczema pathogenesis. This review aims to summarize the current state of knowledge regarding the role of FLG mutations in ichthyosis vulgaris, atopic eczema, and other skin disorders, with an emphasis on potential clinical applications. Further research is needed to clarify the precise role of filaggrin in skin and systemic atopic disease, to pave the way for novel therapeutic interventions.

"Pediatric blaschkitis": expanding the spectrum of childhood acquired Blaschko-linear dermatoses

We describe two young children who developed relapsing, pruritic, papulovesicular eruptions in multiple bands along Blaschko lines on the neck, trunk, and extremities. Skin specimens in both revealed spongiotic dermatitis. This represents the first report of "blaschkitis" in children, providing further evidence that lichen striatus and blaschkitis are related acquired Blaschko-linear dermatoses that exist on a spectrum rather than as the childhood and adult form of a single disease entity. We highlight the features that differentiate blaschkitis from lichen striatus, review the potential roles of cutaneous mosaicism, environmental triggers, and background immunologic state in their pathogenesis, and discuss the spectrum of inflammatory dermatoses that can follow Blaschko lines.

Superimposed segmental manifestation of polygenic skin disorders

In common acquired skin disorders with a polygenic background such as psoriasis, a linear or otherwise segmental arrangement may sometimes be noted. The segmental involvement tends to be rather severe and may be associated with milder, nonsegmental lesions of the same disorder. Such cases may be best explained by an early postzygotic event in the form of loss of heterozygosity involving one of the genes that predispose to the disorder. The following pertinent examples are reviewed in this article: psoriasis vulgaris, pustular psoriasis, atopic dermatitis, lichen planus, systemic lupus erythematosus, pemphigus vulgaris, vitiligo, graft-versus-host disease, granuloma annulare, erythema multiforme, and drug eruption to ibuprofen. Such cases should not be categorized as a "type 2 segmental manifestation" because this term exclusively applies to monogenic traits, whereas in polygenic disorders the more descriptive term "superimposed segmental manifestation" seems appropriate. The concept of early loss of heterozygosity offers a plausible explanation as to why: the segmental involvement tends to appear at a rather young age and often precedes the development of milder, nonsegmental lesions of the same disorder; the segmental lesions are notoriously difficult to treat; and family members may show the disorder in its nonsegmental form. On the other hand, the theory of isolated versus superimposed segmental manifestation may help to elucidate the origin of polygenic skin disorders at the molecular level.