Leprosy in its indeterminate form (I) is a clinical presentation of the disease
preceding the forms described in the Ridley and Jopling (R & J) classification and any
other special forms of leprosy or the reactions. In this chapter, the histopathological and
bacilloscopic characteristics of the I form of leprosy are described, and the main
differential diagnoses are discussed. The histopathological criteria that distinguish the I
form from the other forms of leprosy and the reaction processes that may occur during
the disease course are also discussed. The identification of the histopathological
characteristics of I leprosy is of great importance with respect to the selection of the
treatment. I leprosy should not be confused with other forms of leprosy, especially the
multibacillary forms, which require more prolonged treatment and which can develop
reaction phenomena, causing permanent sequelae.
Keywords: Bacilloscopy, Hansen’s disease, Histopathology, Indeterminate leprosy, Leprosy, Mycobacterium leprae.
