| Rare
cases of Malakoplakia have been reported in the middle ear.
Malakoplakia
(from the Greek malacos,
soft, and placos, plaques) is a rare granulomatous disease that
occurs commonly in the urinary tract. It
was first described by Michaelis and Gutmann in 1902.
Other organs
like the genito-urinary tract, testis, epididymis, lymph nodes,
nasopharynx , tonsil and retroperitoneal tissue have been also
involved though less frequently.
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Pathogenesis:
1) Microorganisms might play a role in the pathogenesis. The
organisms include Escherichia coli (found in more than two thirds of
cases), Mycobacterium tuberculosis , Proteus ,and
Staphylococcus aureus. Specific bacteria are found in certain
categories of patients, for example, coliform bacteria in patients
with chemotherapy and Rhodococcus equi in patients with acquired
immunodeficiency syndrome.
2) An abnormal or altered immune response
has been also implicated in the pathogenesis.
3) The third
hypothesis is an abnormal macrophage response because of defective lysosomal function. It is suggested that macrophages in malakoplakia
are capable of phagocytosis but unable to digest the bacteria.
Partially digested bacteria accumulate in monocytes or macrophages
and lead to the deposition of calcium and iron on residual bacterial
glycolipid.
Gross features:
Grossly, malakoplakia can present as soft tan yellow plaques and
nodules or even extensive bands. The lesion is usually solitary but
can be multiple
Microscopic
features:
Malakoplakia- Histopathology Image
Histologically, it is defined by sheets of histiocytes (Hansemann
cells) with accumulation of granular basophilic periodic acid-Schiff
- positive, diastase-resistant inclusions and calcified
Michaelis-Gutmann bodies, which are pathognomonic but not necessary
for diagnosis. The composition of Michaelis-Gutmann bodies has
been shown to be 94.6% organic and 5.4% inorganic, with the
inorganic components being calcium, phosphorus, and iron. |
