Keratoacanthoma (KA) is a common epidermal tumor that originates from the hair follicle of the skin. It is generally considered as a benign neoplasm, but in rare cases, it can also transform into squamous cell carcinoma. Although surgical excision with a safety margin is considered to be the gold standard treatment for most subtypes of KA, several other treatment options are also available. Intralesional therapy is one of these options, which could be cosmetically and functionally a better alternative to surgical removal, while it provides similar outcomes. It is more effective than topical treatments, yet fewer side effects may be seen than in systemic treatments. Based on the literature, the most commonly used intralesional agent is methotrexate, followed by 5‐fluorouracil and interferon alpha. Regardless of the advantages, which make intralesional therapy a desirable treatment alternative, guidelines for the intralesional treatment of KA are not yet established. A histopathological confirmation before the start of treatment is still recommended to prevent any possible misdiagnosis of KA for SCC. In our present study, we set out to review the current state of the art of the intralesional treatment of KA.

Pseudoxanthoma elasticum (PXE, OMIM 264800) is a rare autosomal recessive disorder with ectopic mineralization and fragmentation of elastin fibers. It is caused by mutations of the ABCC6 gene that leads to decreased serum levels of inorganic pyrophosphate (PPi) anti-mineralization factor. The occurrence of severe complications among PXE patients highlights the importance of early diagnosis so that prompt multidisciplinary care can be provided to patients. We aimed to examine dermal connective tissue with nonlinear optical (NLO) techniques, as collagen emits second-harmonic generation (SHG) signal, while elastin can be excited by two-photon excitation fluorescence (TPF). We performed molecular genetic analysis, ophthalmological and cardiovascular assessment, plasma PPi measurement, conventional histopathological examination, and ex vivo SHG and TPF imaging in five patients with PXE and five age- and gender-matched healthy controls. Pathological mutations including one new variant were found in the ABCC6 gene in all PXE patients and their plasma PPi level was significantly lower compared with controls. Degradation and mineralization of elastin fibers and extensive calcium deposition in the mid-dermis was visualized and quantified together with the alterations of the collagen structure in PXE. Our data suggests that NLO provides high-resolution imaging of the specific histopathological features of PXE-affected skin. In vivo NLO may be a promising tool in the assessment of PXE, promoting early diagnosis and follow-up.