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Sarcoidosis or Tuberculoid leprosy?


Dr. Mona Abdel-Halim

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It is common in our practice as dermatopathologists to receive specimens with a differential diagnosis of sarcoidosis vs. tuberculoid leprosy for histopathological verification. Interestingly enough, on mere morphological basis, one might be unable to differentiate between these two conditions.

Both present with non caseating granulomas. Whereas, sarcoidosis is typically characterized by discrete uniform naked granulomas, tuberculoid leprosy granulomas tend to be oval and surrounded with dense lymphocytic infiltrate and are usually seen around nerves. However, as usual in dermatopathology, diseases do not follow exactly textbooks. Granulomas in sarcoidosis may be lymphocyte rich, may be oval in shape and may be seen around nerves making differentiation from tuberculoid leprosy difficult.

In such conditions, morphological clues of sarcoidosis include the discrete uniform nature of the granulomas, the presence of foci of fibrinoid necrosis and the presence of perigranulomatous fibrosis. Although, granulomas in sarcoidosis may surround nerves, this is not associated with evident nerve destruction which is typical of tuberculoid leprosy. Confirmation of nerve destruction sometimes requires work up with S100, EMA or silver stains. Detection of lepra bacilli by Fite stain will confirm a diagnosis of tuberculoid leprosy, but sometimes this stain is not available and in some cases of tuberculoid leprosy the organisms are so sparse and may not be found in skin lesions.

Accordingly, it is the constellation of all the findings of the clinical picture, the histopathological morphology and the auxiliary work up that will finalize the diagnosis.
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Mark A. Hurt MD

Posted

Dr. Halim,

This is very instructive. In your experience, how often do you find AFB in lesions you expect to be tuberculous? Second, do you stain for all of these granulomas (I do)? Third, what is your most important lesson learned in evaluating these kinds of lesions?

MAH
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Robledo F. Rocha

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Differentiate microscopically sarcoidosis from tuberculoid leprosy may be a Herculean task. For me as one who lives in a highly endemic area of leprosy, most of the cases don’t represent a great challenge since history, clinical presentation and microscopic features are generally straightforward.
Sometimes, without any reliable data, this differentiation becomes a diagnostic dilemma. In such situations, the features that I use to value in order to construe a diagnosis of tuberculoid leprosy are marked destruction of nerves and elongated granulomata following neurovascular bundles.
I routinely perform Fite-Faraco staining in every single case suspected of leprosy, but it almost always results negative in tuberculoid leprosy.
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Dr. Mona Abdel-Halim

Posted

Dear Dr Mark, unfortunately, staining for AFB is not available in all labs. The clinical presentation aids a lot in our country as we have areas in Egypt endemic with leprosy and we are very familiar with its variable clinical presentation. We use slit smear examination in all our cases of leprosy, however tuberculoid cases are usually negative or paucibacillary. Sometimes differentiation from sarcoidosis is very difficult. I am intending to study S100 and EMA staining in these cases to verify their efficacy in assessing nerve destruction.
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