Lobomycosis Workup

Updated: Mar 07, 2022
  • Author: Manuel Valdebran, MD; Chief Editor: Dirk M Elston, MD  more...
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Workup

Laboratory Studies

Laboratory studies are not required.

Lesions can be gently scraped with a sterile scalpel blade and placed on a microscope slide with a coverslip with or without the use of 10% potassium hydroxide (KOH) or the use of a calcofluor preparation of strips of vinyl adhesive tape may demonstrate the yeast. [13, 54, 76]

Sarmiento-Lacera et al noted the utility of fixing lobomycosis skin biopsies for electron microscopy in 4% glutaraldehyde and post-fixing with 1% osmium tetroxide (OsO4) followed by 0.2% ruthenium tetroxide (RuO4). This technique provided for excellent visualization of cellular structures. [77]

An experimental research technique has been developed to determine the viability of L. loboi to gauge success of therapy. The method uses fluorescein diacetate-ethidium bromide (FD-EB) vital staining and appears to be reliably sensitive and specific for viability determination of L. loboi. [78]

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Histologic Findings

 

Histologic examination reveals a granuloma with mostly histiocytes, multinucleated giant cells (average of 10 nuclei), asteroid bodies (ABs), and numerous fungal cells lined up in rows like a child's pop beads. [18, 74, 79] The identified inflammatory cells in a granuloma show the following frequency: CD68+ histiocytes > CD3+ T lymphocytes > CD4+ T lymphocytes > CB8+ T lymphocytes > CD57+ natural-killer cells > CD79+ plasma cells > CD20+ B lymphocytes. [74]

Granulomas are limited in distribution to the dermis, [63] and a delicate layer of collagen may separate the granuloma from the epidermis. [80] The epidermis can be normal, atrophic, or it may have pseudoepitheliomatous hyperplasia, [80] or its papillae may be short. [63]

Xanthomized histiocytes with clear or finely granular eosinophilic cytoplasm occasionally may be seen. [47]

Necrosis is rarely present. [50] Fungal cells are abundant in the macrophages. [24] The fungal cells are highlighted with Gomori Methenamine silver and periodic acid-Schiff stains. [54] Lymphocytes, plasma cells, and leukocytes are found in small numbers. [18] No nerve infiltration is present, and blood and lymphatic vessels are normal. [18]

The presence of intracellular ABs has been described in infiltrating giant cells in granulomatous conditions, including lobomycosis. These ABs have been confused with similar-appearing structures in pathologic specimens obtained from patients with sporotrichosis. Whereas ABs of sporotrichosis consist of a central yeast surrounded by eosinophilic spicules, ABs of lobomycosis are intracellular filamentous structures that contain lipid myelin figures. [81, 82]

See the image below.

Characteristic histologic appearance of the organi Characteristic histologic appearance of the organism. Courtesy of Dr Roberto Baruzzi, Sao Paulo, Brazil.

 

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