Leprosy pathology

Introduction

Leprosy is a chronic infection caused by Mycobacterium leprae, a must intracellular, Gram positive organism. The main clinical types correlate with a specific histopathological pattern.

Histology of leprosy

Lepromatous leprosy: below normal epidermis and grenz zone, there are sheets or groups of macrophages (Figure 1). Macrophages are abundant pink to pale in color. cytoplasm which corresponds to numerous intracellular (parasitized) organisms (Figure 2). The Associated infiltrate is generally scarce and mainly lymphocytic. In older lesions, macrophages may have bubbling cytoplasm (Figure 2). Unlike tuberculoid leprosy, there are no well-formed granulomas or infiltration of nerves.

Tuberculoid leprosy: there is a tuberculoid or sarcoid granulomatous reaction throughout dermis consisting of some Langhans giant cells, macrophages in tight groups, and few companions lymphocytes (figure 3). The infiltrate can infiltrate widely peripheral nerves (figure 4, arrow), vessels, overlying epidermis and arrectores pilorum.

Indeterminate leprosy: the infiltrate is strongly lymphocytic with a smaller number of epithelioid histiocytes in clusters The infiltrate often involves peripheral nerves. The organisms are usually very difficult to find.

Erythema leprous nodosum: shows a dense infiltrate that extends towards the subcutis, particularly around the vasculature. In addition to the epithelioid histiocytes with large bubbly pink cytoplasm seen in other clinical types, there is a polymorphous population of acute and chronic inflammatory cells.

Special studies for leprosy.

Leprosy organisms can be demonstrated with a modified Ziehl-Neelsen (Wade-Fite) stain. Lepromatous leprosy lesions will show numerous organisms that are easy to identify. Cases of tuberculoid, indeterminate, and erythema nodosum leprosum can be difficult as the organisms may be rare. Polymerase chain reaction (PCR) studies may be useful in confirming the diagnosis of leprosy.

Differential diagnosis of leprosy pathology

Granulomatous disorders: Tuberculoid leprosy may resemble sarcoidosis or other granulomatous disorders. Special studies and clinical correlation can help in difficult cases.

Histiocytic reactions: the foamy histiocytes, laden with organisms in lepromatous leprosy, can mimic the histiocytic reactions seen with statement aluminum chloride (a common antiperspirant and hemostatic agent) or orthopedic hardware.

Tuberculosis and other mycobacterial infections: Other mycobacterial infections often cause tissue necrosis and are associated with suppuration. M. avium complex can closely mimic lepromatous leprosy. Special studies can help in the differential.

Lymphoma – T cell Lymphomas may be neurotropic and associated with scattered histiocytes, producing a pattern similar to indeterminate leprosy. Sometimes special studies are needed to reveal a T cell clone and/or isolate the organisms.