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Background: Differentiating lymphocytic scarring alopecias may be difficult clinically as well as histopathologically. Objective: To investigate plasmacytoid dendritic cell (PDC) presence and distribution patterns and their diagnostic value in differentiating scarring alopecias of lupus erythematosus (LE) from lichen planopilaris (LPP) and frontal fibrosing alopecia (FFA). Methods: Seventeen LE-associated alopecia, 20 LPP and 10 FFA cases were immunohistochemically tested for PDC presence/distribution and activity. Results: LE-associated alopecia showed increased PDC content (≥10% PDCs in all cases and ≥50% in 94% of cases), PDC clusters (100% of cases), and deeper dermal and perieccrine distribution (100% of cases) with involvement of the dermoepidermal junction (DEJ, 94% of cases), while the majority of LPP and FFA had <10% PDC content that was mainly confined to the upper dermis surrounding the hair infundibulum with rare DEJ involvement and rare clustering. Conclusions: Specific PDC-related parameters may serve as a useful diagnostic adjunct in the differentiation between LE-associated alopecia versus LPP and FFA.

Skin biopsy is a common dermatologic procedure that is typically required to assess cutaneous neoplasms and to evaluate indistinct skin eruptions for which a clinical differential diagnosis is considered. Although plenty of literature exists on the histopathologic features of different skin diseases, clues and methods that help maximize the diagnostic results and avoid common pitfalls in the processing of skin biopsies have received little attention. In cutaneous biopsy, interpretation is very important, as is the process of choosing the appropriate biopsy technique. As soon as the decision to perform a skin biopsy is taken and until microscopic slide evaluation occurs, multiple opportunities for error may arise, any of which may disadvantage the pathologist in efforts to reach a definitive diagnosis. Therefore, it is exceptionally important that clinicians work closely with pathologists to optimize biopsy results. The purpose of this review is to increase awareness of the potential for error in the course of obtaining and interpreting biopsy specimens. The process consists of several steps that refer to, respectively: choice of biopsy site; choice of technique; tissue fixation; tissue processing; the pathologist's interpretation; and clinicopathologic correlation. Avoiding these pitfalls may, in turn, maximize the pathologist's ability to make the correct diagnosis and thus provide better patient care.

Pure hair and nail ectodermal dysplasia (PHNED) is a rare genetic disorder characterized by hypotrichosis or complete alopecia, as well as nail dystrophy. Mutations in the type II hair keratin gene KRT85 and the HOXC13 gene on chromosome 12q have recently been identified in families with autosomal-recessive PHNED. In the present study, we have analyzed a consanguineous Syrian family with an affected girl having complete alopecia and nail dystrophy since birth. The family clearly showed linkage to chromosome 12q13.13-12q14.3, which excluded the KRT85 gene. Sequencing of another candidate gene HOXC13 within the linkage interval identified a homozygous frameshift mutation (c.355delC; p.Leu119Trpfs*20). Expression studies in cultured cells revealed that the mutant HOXC13 protein mislocalized within the cytoplasm, and failed to upregulate the promoter activities of its target genes. Our results strongly suggest crucial roles of the HOXC13 gene in the development of hair and nails in humans.

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