Psoriasis is a common chronic relapsing inflammatory cutaneous disease; the main role in the inflammation of this condition is played by lymphocyte Th1, Th17 and their cytokines. The activity of these cells is modulated by a particular kind of T cells recently described: the T regulatory cells (T_reg). These are able to inhibit the immunological response and to maintain the cutaneous immunological homeostasis, thus preventing autoimmunity against self antigens. Few data are available in the literature as to T_reg in psoriasis; several studies demonstrate that the function of these cells is impaired in this condition and treatments for psoriasis may increase the number and activity of T_reg. The role of these cells in the pathogenesis of psoriasis is very important to understand how they may contribute to the development of this cutaneous disorder. In the near future it would be possible to target therapies at these defects, improving the activity of these cells and maintaining cutaneous homeostasis, preventing psoriasis or other inflammatory cutaneous conditions.

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Background: Current literature addressing dermatologic conditions associated with Down syndrome is limited, with emphasis on rare skin conditions and lack of consensus on the incidence of more common disorders. Objective: We sought to evaluate dermatologic conditions in patients with Down syndrome diagnosed and managed by dermatologists. Methods: This was a retrospective analysis of 101 pediatric and adult patients with Down syndrome seen by the University of Massachusetts Dermatology Department between 2008 and 2018. Results: Folliculitis was the most common diagnosis overall (30.7%), followed by seborrheic dermatitis (26.7%) and hidradenitis suppurativa (22.8%). Eczematous dermatitis, alopecia areata, and xerosis were the most common diagnoses observed in children aged 0-12 years; hidradenitis suppurativa, folliculitis, and seborrheic dermatitis in adolescents aged 13-17 years; and folliculitis, seborrheic dermatitis, and xerosis in adults 18 years and older. Other notable diagnoses present overall included onychomycosis (9.9%) and psoriasis (8.9%). Malignant cutaneous tumors were present in two patients, specifically basal cell carcinoma and malignant melanoma in situ. Limitations: This was a retrospective, single-institution study. Conclusion: Dermatologic conditions in patients with Down syndrome vary by age but are most often adnexal and eczematous disorders. Trisomy of chromosome 21 and the resulting downstream effects, specifically on the immune system, may account for these findings.

Cutaneous mixed tumor (chondroid syringoma) is the cutaneous counterpart of pleomorphic adenoma of salivary glands, comprised of both epithelial and mesenchymal components. Malignant transformation is exceptionally rare, with only a few cases reported. We report a case of a malignant cutaneous mixed tumor in an 86-year-old white man who presented with a pink indurated plaque on his left scapula. He had a history of nonmelanoma skin cancers, a stage IB malignant melanoma of a lower extremity and Gleason 4 + 3 prostate cancer treated with brachytherapy, external beam irradiation, and bicalutamide. A shave biopsy was performed and histologic examination revealed infiltrative single-unit atypical cells and small ducts in a superficially transected sclerotic dermis suggestive of a poorly differentiated adenocarcinoma. No epidermal connection was identified. Immunohistochemical studies revealed that the tumor was positive for CK7, CAM5.2, and mCEA and negative for CK20, epithelial membrane antigen, P63, prostate-specific antigen, prostatic specific acid phosphatase, and alpha-methylacyl-coenzyme A racemase. A metastasis of the breast or upper digestive tract was favored, although a primary eccrine carcinoma was also considered. Imaging was performed and no other masses were identified. A slow Mohs excision was performed with negative margins. Microscopic examination revealed a biphasic neoplasm comprised of infiltrative epithelial strands and tubules consistent with an eccrine carcinoma in a hyalinized and chondromyxoid stroma within the dermis, arising from a well-circumscribed chondroid syringoma located in the deep dermis and subcutis. Areas of clear cell change, intracytoplasmic vacuolization, and mucin pools were noted. Multiple foci of perineural invasion were identified. Additional immunohistochemical studies revealed that the tumor was positive for S100 and negative for CK5/6, calponin, glial fibrillary acidic protein, GATA3, GCDFP-15, and mammoglobin. Based on the morphologic features and immunoprofile, this was diagnosed as a malignant cutaneous mixed tumor. This case highlights the importance of obtaining adequate tissue for histologic evaluation, as they can be confused with other skin neoplasms because of their clinically ambiguous presentations. Although rare, an accurate diagnosis is important given that long-term follow-up is recommended because of the risk of local recurrence and both lymph node and distant metastases.

Keratoacanthoma (KA), an epithelial neoplasm occurring in sun-exposed skin of the elderly, is considered a well-differentiated form of conventional squamous cell carcinoma (SCC) that often follows a course of spontaneous regression. Distinguishing KA from conventional SCC or pseudocarcinomatous epithelial hyperplasia ensures proper diagnosis, treatment and management. For some time, perforating elastic fibers have been utilized in differentiating KA from SCC. This phenomenon may also occur in association with scars and hypertrophic lupus erythematosus (LE). To assess the diagnostic utility of perforating elastic fibers, we compared their incidence in KA, SCC, scars with overlying pseudocarcinomatous hyperplasia, hypertrophic LE, hypertrophic lichen planus (LP) and lichen simplex chronicus (LSC). A retrospective case search identified 359 lesions and the presence of perforating elastic fibers was evaluated using routinely stained sections. This phenomenon was documented in all studied groups except hypertrophic LP. The incidence was found to be 71% in KA, 37% in SCC, and was lowest in inflammatory conditions with associated pseudocarcinomatous hyperplasia (hypertrophic LP 0%, hypertrophic LE 5.9% and LSC 28.2%). The observed frequency in pseudocarcinomatous hyperplasia overlying scars (57.8%) vs. KA (71%) was not statistically different. Although elastic fiber trapping has potential value as a diagnostic criterion for KA, dermatopathologists should consider its limitations. Its diagnostic utility was greatest in distinguishing KA from hypertrophic LE and hypertrophic LP. Conversely, elastic trapping is not helpful differentiating pseudocarcinomatous hyperplasia from recurrent/persistent KA following surgery.