Leprosy: a diagnostic trap for dermatopathologists in nonendemic area

Leprosy is a chronic infectious disease caused by Mycobacterium leprae, presenting with different clinicopathological forms. These great variety of presentations make the diagnosis of leprosy a difficult challenge in countries where the disease is not endemic. Moreover, a discordance between the clinical and histopathological diagnosis in classifying a case of leprosy can complicate the issue. We report a 43-year-old woman in whom the diagnosis of leprosy was challenging, especially, because the biopsy was sent without any clinical suspicion and Italy is a nonendemic area. The clinical informations described simply an annular lesion, and histopathology disclosed a superficial and deep moderate perivascular and periadnexal infiltrate in the dermis, predominantly made of lymphocytes with some histiocytes, in the absence of granuloma formation, foamy histiocytes, or giant cells. Only the clinicopathological correlation based upon the patient's family history, her Brazilian origin, and her anesthetic lesions led us to the suspicion of leprosy. We reviewed the slides with more serial cuts and with special stains that eventually revealed a slight perineural lymphohistiocytic infiltrate and the presence of rare bacilli in the nerves, more consistent with indeterminate leprosy. However, the clinical features and the detection of just few bacilli in the skin lesions and skin smears were more consistent with a borderline leprosy. The discordance between the clinical and histopathological diagnosis in the setting of leprosy is discussed.