Background: Lepra reactions are not always diagnosable under the microscope. We analyzed skin histopathology in 64 cases of lepra reaction.
Aim: To make detailed observations on histopathologic features of type 1 and type 2 lepra reaction (erythema nodosum leprosum, ENL).
Materials and methods: In this retrospective study, we included 64 patients diagnosed during a 3-year period as lepra reaction based on clinico-pathological co-relation.
Results: Out of the 64 patients, 22 were of type 1 reaction and 42 of ENL. The most consistent finding in type 1 reaction was papillary dermal edema (86%) followed by pyknosis of lymphocytes (77%) and intercellular edema within granuloma (73%). Surprisingly, folliculotropism of lymphocytes was seen in 55% and subcutaneous infiltration in 36%. In ENL, the most common finding was presence of neutrophils within the granuloma (100%), followed by leukocytoclasia (81%), papillary dermal edema (81%), and neutrophilic panniculitis (69%). Fibrin in the vessel wall or/and granulomas was noted in only 38% while fibrin thrombi in the vessel walls were seen in only 12% of cases.
Conclusion: Infiltration of macrophage granulomas by neutrophils is a reliable sign of ENL. Classical signs of vasculitis are not always present in ENL. Folliculotropism and lymphocytic panniculitis were frequent in type 1 reactions while neutrophilic panniculitis was common with ENL.
Keywords: Erythema nodosum leprosum; lepra reaction; vasculitis.