Histopathological features of reversal reactions in Morbus Hansen

The reversal reaction on Morbus Hansen is a type IV hypersensitivity reaction to M. leprae antigens. The clinical symptoms of a reversal reaction are that some or all of the existing lesions become more numerous and active in a short time. Hypopigmented lesions become more erythematous, erythematous lesions become increasingly erythematous, macular lesions become infiltrating, and old lesions increase in size. The histopathological feature of the reversal reaction showing dermal edema, stretching of the granulomas followed by loss of the well form granuloma arrangement, and predominance of lymphocytes are described as the hallmarks of a reversal reaction. Several additional characteristics were obtained in the form of an increase in the number of Langhans giant cells, as well as pyknosis/shrinkage of the lymphocyte nucleus. Although not a diagnostic criterion for a reversal reaction, histopathological examination of a lesion biopsy is needed to differentiate a reversal reaction in Morbus Hansen from other differential diagnoses.