Case 165. Lepromatous leprosy (35 y-o M)
    Biopsy from erythematous and scaling nodules on the extremities of a Paraguaian Nisei    
Key words : 
Mycobacterium leprae, lepromatous leprosy, tuberculoid leprosy, Fite method    
Mildly elevated indurating nodules are seen on the face and extremities (gross findings).   Infiltration of foamy histiocytes (xanthogranuloma) is seen in the dermis. The papillary dermis is spared (HE).
The xanthogranulomatous lesion is formed around nerve fascicles in the deep dermis, an important hint for the diagnosis of leptomatous leprosy (HE).   For the reproducible histochemical identification of Mycobacterium leprae, the Fite's variation of Ziehl-Neelsen stain, employing oil xylene for deparaffinization, should be applied.
When the deparaffinization is done in a routine way, acid-fastness of M. leprae is markedly diminished (Ziehl-Neelsen, regular method). Compare the result with the Fite's variation.   The bacilli are densely clustered within the cytoplasmic vacuoles of foamy histiocytes. This unique structure called "globi" is demonstrated by the Fite method of Ziehl-Neelsen stain.
The bacilli forming "globi" are stained with PAS method.   The "globi" are also clearly stained with colloidal iron sequence, since M. leprae utilizes hyaluronic acid as a source of proliferation.
Mycobacteria consisting of "globi" are strongly stained with immunostaining for BCG antigens. The antiserum available from DakoCytomation is widely cross-reactive to Mycobacterium species.   Immunoelectron microscopic study demonstrates positively labeled bacilli in the cytoplasm of a foamy histiocyte (pre-embedding method using a paraffin section).
Reference case 165A
Lepromatous leprosy in a Cambodian young guy, presenting multiple skin nodules and depigmentation spots. Incision can be done easily because of decreased sensation. Stamp preparation of the exudate from the skin incision (skin smear test) can be used for the quick and sensitive diagnosis of leprosy.
  Reference case 165A
Ziehl-Neelsen stain for the smear preparation reveals acid-fast bacilli in and outside macrophages. Lepromatous leprosy is also called as the multibacillary type, while the tuberculoid leprosy is categorized as the paucibacillary type.
Reference case 165B
Tuberculoid leprosy seen in a 74 y-o Japanese male, presenting numbness of right hand (gross findings). Erythematous swelling and decreased sensation of the right middle finger are observed.
  Reference case 165B
Skin biopsy shows intradermal formation of epithelioid granulomas without caseous necrosis (HE). The papillary dermis is involved. Acid-fast staining is negative. Diagnostic hints include clinical information of numbness and histologic identification of nerve involvement by the granulomatous lesion.