Drug‐Induced Blaschkitis Associated With Dipeptidyl Peptidase‐4 Inhibitor: A Case Report and Review of the Literature

Blaschkitis is an acquired Blaschko-linear inflammatory dermatosis similar to classic lichen striatus. Although the pathomechanisms have not yet been fully elucidated, it has been reported that some cases were triggered by viral infections, vaccines, or drugs. We recently encountered a patient who developed multiple broad bands of erythematous papular plaques accompanied by vesicles along Blaschko lines on the left side of the trunk while taking sitagliptin, a dipeptidyl peptidase-4 inhibitor (DPP-4i) for type 2 diabetes mellitus. Histopathology showed necrotic keratinocytes in the epidermis accompanied by subepidermal blisters with infiltration of CD8-positive T cells and eosinophils in the upper dermis. Negative direct and indirect immunofluorescence ruled out DPP-4i-associated bullous pemphigoid. Within 1 week after withdrawal of DPP-4i, the skin lesions resolved, with no subsequent relapse. Furthermore, the distribution of the lesions along Blaschko lines is suggestive of cutaneous mosaicism and may be associated with immune-inflammatory responses induced by DPP-4i. Based on the clinical characteristics of this case, we speculate that DPP-4i activated T lymphocytes, which subsequently reacted to mosaic skin areas and induced blaschkitis. Accordingly, the diagnosis was DPP-4i-associated blaschkitis. We report this case together with a review of the relevant literature on drug-induced blaschkitis and lichen striatus.