Mid borderline leprosy in type Bα Blaschko linear pattern: a rare phenomenon

Introduction Leprosy is a chronic granulomatous disease caused by M. leprae. It is a great imitator as it can manifest in different unusual and atypical ways. Mid borderline leprosy (BB) is an unstable form representing the immunologic midpoint in the clinical spectrum. Case report Here, we report a case of BB leprosy having classical inverted saucer‐shaped lesions elsewhere on the body with a linear psoriasiform lesion over the left forearm following the lines of Blaschko. Biopsy from this lesion revealed granulomas consisting of equal admixture of epithelioid cells and macrophages without multinucleate giant cells suggesting mid borderline leprosy. Conclusion Occurrence of lesions in a Blaschko linear pattern supports the role of genetic susceptibility to leprosy. The genetically vulnerable cells along the lines of Blaschko were infected while the surrounding cells remained unaffected. This explains the concept of locus minoris resistentiae due to cutaneous mosaicism.