Erosive Pustular Dermatosis of the Scalp Arising on Long-Standing Burn Scars: A Report of Three Cases and Brief Review of Literature

Abstract Introduction: Erosive pustular dermatosis of the scalp (EPDS) is a rare and recalcitrant condition in which chronic scalp pustules and erosive patches are diagnosed by nondiagnostic laboratory tests and histopathological tests. Although various precipitating factors including trauma have been reported, erosive pustular dermatosis arising on the long-standing burn scars is rare. Case Presentation: We report three cases of EPDS arising on long-standing burn scars. Based on clinical and histological findings, erosive pustular dermatosis was diagnosed and successfully treated with topical steroid ointment. Conclusion: We propose that chronic burn scar is another precipitating factors for EPDS and clinicians should consider EPDS in differential diagnoses of erosive pustular dermatosis in long-standing burn scars on the scalp. Established Facts Erosive pustular dermatosis of the scalp is rare, and the exact pathogenesis remains unknown, although trauma or actinic damage has been suggested.

that lead to destruction of hair follicles and scarring alopecia.Because the exact pathogenesis of EPDS is unknown, previous studies have described the associations between EPDS and various predisposing factors, including trauma, actinic damage, immunosenescence, and autoimmune diseases [2].However, EPDS arising on childhood burn scars has rarely been reported.We present three cases of EPDS arising on preexisting longstanding burn scars of the scalp.

Case Report
Case 1 A 66-year-old Asian woman presented with atrophic confluent scalp erosions with crusts arising on a long-standing burn scar (Fig. 1a).The patient reported that the burn scars occurred 60 years prior, and she had recently bumped into a desk.A biopsy specimen showed subcorneal pustule, ulcer, and neutrophilic infiltration in the dermis (Fig. 1b).She was treated with topical clobetasol propionate, oral cephalosporin, and intralesional corticosteroid injection.After 8 weeks, inflammatory signs regressed, and the lesions healed with scarring.During 63 months of follow-up, EPDS lesions relapsed after the patient dyed her hair.

Case 2
A 79-year-old Asian woman presented with a 10-month history of persistent scalp plaques with crusts, pustules, and erosions arising on a childhood burn scar (Fig. 2a).Histopathological examination showed ulcer and neutrophilic infiltration in the dermis (Fig. 2b).She was treated with clobetasol propionate and 0.1% tacrolimus ointment.One month later, the lesions showed rapid improvement.

Case 3
A 57-year-old Asian woman who presented with a 1-month history of ill-defined erythematous scalp patches with erosions, crusts, and pustules arising on a childhood burn scar (Fig. 3a).
The patient reported that the burn scars occurred 55 years prior and denied recent trauma history.Histopathological examination revealed microabscess within the hair follicles and inflammatory infiltrates in the dermis (Fig. 3b).She was treated with topical clobetasol propionate, oral prednisolone (20 mg/ day), and minocycline (100 mg/day).After 7 days, the eroded surface improved, and oral prednisolone was tapered.One month later, we initiated systemic isotretinoin (10 mg/day), and there have been no signs of recurrence after 10 months of follow-up.

Discussion
EPDS was first described by Burton and Pye in 1979 [1], and it manifests as pustules, ulcers, erosive patches, and thickened crusts, which lead to scarring alopecia.Because of its rarity and diagnostic challenges, the exact incidence of EPDS remains unknown.However, the number of reports is increasing, suggesting underdiagnosis of EPDS [3].EPDS is diagnosed based on high clinical suspicion and diagnosis of exclusion after ruling out other conditions by histologic examination and microbial cultures.The most common differential diagnosis includes bacterial or fungal infection, squamous cell carcinoma, folliculitis decalvans, pemphigus foliaceus, cicatricial pemphigoid, impetiginized eczema, pustular psoriasis, dermatitis artefacta, and pustular pyoderma gangrenosum.
Histopathologic findings often are non-specific, but skin biopsy is important to exclude other differential diagnosis.In the early stage, the epidermis shows hyperkeratosis and psoriasiform hyperplasia, and the papillary dermis presents a mixed inflammatory infiltration composed of neutrophils and lymphocytes ).We received the patient's consent form about publishing all photographic materials.[3].Over time, atrophic epidermis, extensive fibrosis, and absence of pilosebaceous units are observed.Although the clinical presentation of EPDS is similar to a bacterial or fungal infection, bacterial and mycologic cultures often reveal only normal flora, and even when isolated, responsiveness to appropriate antibiotics is poor.These observations suggest that the microorganisms represent a secondary colonization rather than primary infection [4].In our cases, the lesions showed pustules, ulcers, and erosive patches arising on a childhood burn scar.To exclude the possibility of cutaneous malignancy within a burn scar (Marjolin ulcer), we performed a skin biopsy, and histopathologic examination showed non-specific inflammatory reactions.Table 1 summarizes the clinical and histopathologic features of our cases.Based on clinical and histopathologic features, EPDS was diagnosed.
Although the pathogenesis of EPDS remains unknown, actinic damage, trauma, immunosenescence, androgenetic alopecia, hormones, and autoimmune diseases have been regarded as predisposing conditions [2,3].Considering classic clinical features and histopathologic findings, actinic damage and androgenetic alopecia were the common predisposing factors [3,5], and associated skin atrophy and aberrant wound healing are considered key causes of EPDS.The most widely accepted hypothesis is that physical damage to the actinic or atrophic skin induces delayed wound healing or chronic ulcers that stimulate immunologic dysregulation and abnormal neutrophil chemotaxis against unknown skin antigens [5,6].There have been several studies focused on the association between hair follicles and development of EPDS, and some authors focused on immunologic dysregulation toward the hair follicles induced by trauma with subsequent chronic inflammation [7].Recently, another study revealed that a key histologic feature of EPDS is destruction of hair follicles [5], which act as a reservoir for keratinocytes and as wound healing promoters [6,8].Burn scar tissue is composed of hyalinized collagen and decreased elastic fibers, vessels, and adnexal structures [9].With less elasticity and decreased re-epithelialization, a burn scar is damaged easily by trauma and heals slowly.Considering burn scars are susceptible to injury, repetitive irritation could cause erosions or ulcers, which trigger abnormal autoimmune reactions and persistent erosive dermatosis.EPDS arising on burn scars susceptible to injury and with decreased hair follicle density not only emphasizes the association between hair follicles and development of EPDS, but also highlights the importance of aberrant wound healing as an important predisposing factor.Although it is not possible to determine whether decreased hair density precedes EPDS or whether immunologic dysregulation against hair follicles occurs in EPDS, this study emphasizes the importance of hair in the pathogenesis and reports longstanding burn scars as a new precipitating factor of EPDS.Due to its tendency to recur, treatments for EPDS often focus on reducing inflammation and preventing progression of scarring alopecia [3].Ultrapotent and potent topical corticosteroids are the most frequently used and effective treatment for EPDS, but skin atrophy and telangiectasia could be problematic in long-term use.Topical calcineurin inhibitor has the advantage of a better safety profile than topical corticosteroids as a maintenance therapy [10].Although there have been few reports about vitamin A derivates (i.e., acitretin and isotretinoin) [11], calcipotriol [12], and photodynamic therapy [13], prospective controlled trials have been limited.
Here, we propose that chronic burn scar is another precipitating factor for EPDS and recommend that clinicians consider EPDS in differential diagnoses of erosive pustular dermatosis in long-standing burn scars on the scalp.To clarify the pathogenesis of EPDS, multicenter, epidemiological studies about the association between EPDS and hair follicle destruction are needed.

Statement of Ethics
This study protocol was reviewed and approved by the Ethics Committee and Institutional Review Board at Kangbuk Samsung Hospital, Seoul, Korea (approval No. KBSMC-2023-04-004).

Fig. 1 .
Fig. 1. a Multiple erosive lesions with black-colored, lupoid, thick crusts on the vertex of a 66-year-old female patient at baseline and 8-week follow-up.b Histopathological examination revealed hyperkeratosis, subcorneal pustules, ulcer, and neutrophilic infiltration in the dermis (hematoxylin-eosin [HE], original magnification: ×100).We received the patient's consent form about publishing all photographic materials.

Fig. 2 .Fig. 3 .
Fig. 2. a Multiple keratotic plaques with crusts, pustules, and erosions on the vertex of a 79-year-old female patient at baseline and 4-week follow-up.b Histopathological examination revealed ulcer, acanthosis, and neutrophilic infiltration in the dermis (hematoxylin-eosin [HE], ×100).We received the patient's consent form about publishing all photographic materials.

Table 1 .
Summary of clinical and histopathologic features of our cases