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Hansen’s Disease
Hansen’s disease is a study in the relationships between immune status and histologic patterns. It is a disease manifested in the histologic features of a cell-mediated immune
response but, in making this assessment, it would be inaccurate to assume that there is no role for humoral factors. In fact, plasma cells are a part of the reaction in the skin, as well as in other organ systems.
They are a prominent feature of the changes in lymph nodes; hypergammaglobulinemia also is a feature of the disease. The common approach to the morphology of the disease emphasizes polar expressions with gradations
among the poles. From a clinically ambiguous expression of early disease (indeterminate leprosy) (S11C6P1-1, & S11C7P2-1 & 2), the subsequent patterns range from tuberculoid (S11C9P4-1-3), to borderline (S11C8P3-5, & S11C10P5-1-4), to lepromatous (S11C6P1-1-4, & S11C7P2-3-5), not necessarily in that order. Tuberculoid leprosy is rare in comparison to borderline and lepromatous leprosy. In
tuberculoid leprosy, the infiltrates extend to the dermal-epidermal interface; giant cells are a prominent feature (S11C9P4-1-3). In
lesions of leprosy, the load of bacilli is proportional to the integrity of the immune response, particularly cell-mediated immunity. The disease is manifested in tuberculoid patterns (acidophilic histiocytes
clustered in granulomatous patterns, including tubercle-like patterns) (S11C6P1-5 & 6); in diffuse infiltrates of foamy histiocytes
(S11C7P2-6 & 7, & S11C8P3-1 & 2); or in
combinations of the two. It is tempting to interpret the lepromatous patterns as evidence of a failing immune system in response to a heavy load of bacilli (a blockade of the reticulo-endothelial system), but the
relationships are difficult to define. The identification of inflammatory infiltrates involving peripheral nerves (often with hyperplasia of Schwann and perineurial cells) is an aid in diagnosis for cases in which
organisms are few in number (S11C6P1-7)
The chronic manifestations of Hansen’s disease may be modified by reactions, by nodular panniculitis (erythema nodosum leprosum), or by the Lucio phenomena. The
latter two processes may be evidence of immune-complex disease.
In patients who have received treatment, the disease may stabilize; in the event, the histologic changes become less impressive. Rarely, lesions, which have stabilized following
treatment, become nodular; they show a lepromatous pattern in a background that has fibrohistiocytic qualities (S11C8 3P-4); this type
of disease, in a patient who has developed resistance to drug therapy, is histoid leprosy.
When I think of leprosy, I think of Dick Mansfield
and the interest he had in the subject. I am indebted to Dick for some of the histologic sections used in the preparation of this material. He is not to blame for the poor quality of the photomicrographs. I suppose, if I were to ask Dick whom he thinks of in reference to this disease, he would name Chapman Binford.
Modlin RL, Rea TH: Leprosy: new insights into an ancient disease. J Am Acad Dermatol 1987;17: 1-13.
Granulomatous Dermatitis
(Variations)
Granulomas are variable in their patterns. For some disorders, infiltrates are rich in histiocytes, but the cells are loosely arranged and rounded in outline; these patterns are
commonly classified as granulomatous. If activated histiocytes in epithelioid patterns (closely aggregated histiocytes that are molded against their neighbors and are not associated with appreciable intercellular
matrix) are a requisite for the diagnosis of granuloma, diffuse, loose infiltrates do not qualify; such lesions (i.e., those with diffuse infiltrates) might be better characterized as histiocytic dermatitides;
examples would include the infiltrates of granuloma inguinale (S11C14P9-1-6), and malakoplakia.
An important variation of a granuloma is a process showing focal areas of suppuration, with epithelioid histiocytes in palisades about the areas of suppuration. Such lesions qualify
as suppurative granulomas (S11C10P5-5); they are important as a marker for infectious processes. In the face of suppurative
granuloma, the burden of proof would be on both the pathologist and the clinician to exclude an infectious process.
Another variation is the granuloma with central, acellular, acidophilic necrosis and with palisades of epithelioid histiocytes at the periphery of the zone of necrosis. These
associations may be seen in lesions of tuberculosis in which the central zone of necrosis often is characterized as caseous necrosis. On the other hand, similar patterns may be seen in lupus miliaris disseminatus facei (S11C10P5-6), without the implication that there is an associated, demonstrable pathogen.
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