1. General introduction 18 factors that may play a role in the choice of NFI in clinical practice are costs and ease of use, for example SLIs are relatively easy to use, mobile and cheap. In the more innovative EPIs the volume and pressure can be adjusted, enabling more controlled and reliable drug delivery. The downside is that they are not portable, and relative expensive compared to the first generation SLIs. However, EPIs have shown to facilitate more standardized and consistent drug delivery compared to SLIs. Clinical endpoints In order for a treatment to be effective for keloids, it is important that the reticular dermis is reached.44 A previous ex vivo study by Bik et al. has shown that the formation of a papule is an immediate skin response that is directly visible after NFI-assisted injections, and indicates successful dermal drug delivery in normal skin.29 Therefore, it can be used as clinical endpoint when using NFI. However, the direct skin responses in keloids have not yet been studied, and may differ from normal skin because the fibrous tissue can be very thick and rigid. Intralesional corticosteroid treatment The most commonly used therapy for keloids is intralesional corticosteroid treatment using conventional needle injections, of which triamcinolone acetonide (10 to 40 mg per ml) is most frequently used.45 It is easy to perform, widely available and relatively cheap.46,47 Corticosteroids induce keloid regression through several mechanisms: suppression of inflammation by inhibition of cytokines, vasoconstriction which induces hypoxia, and inhibition of keratinocytes and fibroblasts proliferation due to its antimitotic effect.48,49 Overall, intralesional corticosteroids offer an effective treatment for keloids, and response rates vary from 50 to 100% after one year.49 However, recurrence rates appear to be high, and range from 33%–50% after five years.50 Moreover, intralesional corticosteroids appears to be less effective in severe keloids, and local adverse events such as fat atrophy,
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