Adult Blaschkitis With Lichenoid Features and Blood Eosinophilia

There have been many reports of congenital and acquired dermatoses that trail Blaschko lines. Lichen striatus is representative of an acquired cutaneous linear inflammatory dermatosis running along the lines of Blaschko, characterized histopathologically by the predominance of lichenoid infiltration. Adult blaschkitis, however, is considered under the same disease spectrum as lichen striatus and is characterized by a spongiotic reaction pattern. Few differences have been recognized between lichen striatus and adult blaschkitis such as age of onset, triggers, distribution, histopathology, and response to treatment. A case of male patient with adult blaschkitis presenting as unilateral asymptomatic erythematous edematous papules, papulovesicles, and plaques over Blaschko’s lines, in which skin biopsy revealed coexistent pathological features of lichen striatus and adult blaschkitis along with blood eosinophilia, has been presented here. This may add to the cumulative evidence on the pathogenesis of adult blaschkitis as an allergic reaction to an unknown inciting allergen. Evidence to consider adult blaschkitis as part of the lichen striatus spectrum is growing. Triggers for such skin reactions remain diverse. This case presentation suggests that adult blaschkitis could be triggered by an allergic response evidenced by the blood eosinophilia when other causes of eosinophilia are excluded.


Introduction
Blaschko's lines (BL) are considered systematized cutaneous developmental patterns during embryogenesis that are different from vascular, neural, or lymphatic pathways. The BL were described and drawn by Alfred Blaschko, a German dermatologist, in 1858-1922 [1,2].
Blaschkolinear acquired inflammatory skin eruption (BLAISE) is a cluster of disorders consisting of various inflammatory skin diseases including lichen striatus (LS), adult blaschkitis (AB), lichen planus (LP), psoriasis, lichen nitidus, atopic dermatitis, lupus erythematosus, and graft-versus-host disease [4]. We report a case of AB with coexisting pathological features of LS and transient blood eosinophilia, which resolved with the clearing of skin lesions, suggesting an allergic reaction as a possible trigger for the blaschkitis or an associated feature of the skin presentation since other causes of eosinophilia were excluded. There was no personal history of atopy, insect bite, drugs, or recent infection, nor a family history of similar presentation. On examination, unilateral erythematous edematous papules, plaques, and papulo-vesicles over the left side of the body were observed, as seen in  The lesions were following BL as whorls and interrupted lines. Nails and mucous membranes were spared. Complete blood count (CBC) showed hemoglobin and white blood cell count to be within normal limits and eosinophilia of 10.6%. Additionally, renal and liver functions were normal, hepatitis B screening was negative, and antinuclear antibody and stool analysis were negative.
Biopsy showed parakeratosis, epidermal spongiosis, and mild acanthosis with several necrotic keratinocytes mainly at the lower levels of the epidermis. In the dermis, foci of lichenoid infiltrate at the dermo-epidermal junction were found. Lymphocytic infiltrate was also noted around the eccrine ducts. Additionally, scattered eosinophils (seven eosinophils per 10 high-power fields), some extravasated red blood cells, and no evidence of vasculitis were observed, as seen in Figure 3,

FIGURE 4: Scattered eosinophils (seven eosinophils per 10 high-power fields).
Immunofluorescent studies for IgA, IgG, IgM, C3, and fibrinogen were negative. The lesions resolved with post-inflammatory hyperpigmentation spontaneously within two weeks, as shown in Figure 5. Based on the clinical and histopathological features, the diagnosis of AB with spongiotic dermatitis and the coexistent lichenoid infiltrate with eosinophils was considered. The patient was prescribed topical mometasone cream 0.1% and a poor compliance was reported but was nonetheless satisfied with the outcome. CBC repeated after 12 weeks revealed no eosinophilia and there was no recurrence of lesions.

Discussion
AB is one of the disorders comprising BLAISE along with many others including LS, LP, psoriasis, lichen nitidus, atopic dermatitis, lupus erythematosus, and graft-versus-host disease [4]. AB and LS are still considered under the same disease spectrum; however, few differences have been recognized, such as age of onset, distribution, histopathology, and response to treatment [6][7][8][9] (Table 1). 2021   LS is representative of acquired cutaneous linear inflammatory dermatosis running along the BL, usually in a unilateral fashion and mainly over extremities [6][7][8][9]. LS primarily occurs in children between 5 and 15 years of age. Involvement of the nail in LS is rare and may occur before, concurrently, or after the skin lesion [25]. The affected nail may present as pitting, longitudinal ridging, fissuring, splitting, fraying, striate or punctate leukonychia, overcurving, thinning or thickening of the nail plate, irregular transverse grooves, onycholysis, subungual hyperkeratosis, and nail loss. The presentations may only include the lateral or medial portion of the nail plate of only one digit [25]. The case series reported by Lunge et al. showed resolution of LS lesions within three months of tazarotene use with minimal discomfort due to irritation [26]. Topical steroids had been used for itchy LS lesions with inconsistent results [26]. However, calcineurin inhibitors and calcipotriol with topical or intralesional steroids have been used successfully [26]. Spontaneous resolution of LS had been reported within 3-12 months [26].
We report here a case of AB with spongiotic dermatitis and coexistent lichenoid infiltrate with concurrent tissue and blood eosinophilia. Persistent eosinophilia for more than three months can fall into three categories: reactive, clonal, or syndromic such as hypereosinophilic syndrome [27]. Many diseases including allergic conditions such as atopic dermatitis, drugs, infections, autoimmune, and malignancy could lead to eosinophilia [27]. Clinical history is the most important guide to the cause. The lack of any specific finding that points to the cause of eosinophilia in this case including atopic dermatitis made AB the probable cause of eosinophilia. Eosinophils are rare in LP and its variants; however, some cases of hypertrophic LP have eosinophils in the absence of drug history [28]. Hypertrophic LP is to be included in the differential diagnosis of lichenoid dermatitis with eosinophils [28]. Nonetheless, the lack of pruritis, the morphology of the lesions, the short duration, and histopathology are against LP.
We suggest that this patient presentation could be triggered by an allergic reaction to an unknown inciting agent or a true additional feature of AB and to include it in the differential diagnosis of lichenoid dermatitis with eosinophils. Performing a full blood count of such cases may shed light on the etiology and the features of this disease entity.

Conclusions
In conclusion, AB, a diagnosis subjected to major scrutiny, shares many features with LS and LP. The age of onset, the short duration of the disease, and the histopathological features, all collectively point in favor of AB. Features against LP include the lack of intense pruritis and the clinicopathological features. AB triggers can be diverse; an allergic hypersensitivity reaction could be added to the list and we suggest obtaining eosinophils count to try to understand the triggering factors for such a presentation. Skin eruption resolves spontaneously without treatment with post-inflammatory hyperpigmentation as with our patient and other reported cases. More case reports are needed to understand the triggers of such a presentation to improve our true understanding of the pathogenesis of AB and its associated features.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.