Pediatric Sporotrichosis Workup

Updated: Feb 12, 2019
  • Author: William P Baugh, MD; Chief Editor: Russell W Steele, MD  more...
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Workup

Laboratory Studies

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  • Sporotrichosis is a thermally dimorphic fungus that can be grown from infected tissues.

  • S schenckii is easy to grow and is not sensitive to cycloheximide, which is often added to fungal culture media to inhibit growth of saprophytes and to promote growth of dermatophytes.

  • At 25°C on Sabouraud agar, the fungus forms a white-to-cream–colored mold that turns dark brown or black as it ages, often forming a leathery, wrinkled surface.

  • Microscopic examination of a cotton blue or Scotch tape preparation reveals long and slender septate hyphae with hyaline pyriform conidia, often forming flowerlike arrangements.

  • In tissue at 37°C, S schenckii takes on an elongated yeast form, approximately 6-8 mm in length, with rounded ends resembling cigars. Budding from the main yeast bodies may be observed in the tissues.

  • To confirm the identity of this fungus, the hyphal form may be converted into the yeast phase. This is often best achieved by growing the fungus on brain-heart infusion agar supplemented with sheep's blood then raising the temperature from 25°C to 37°C.

  • Fine-needle aspiration of lymphocutaneous sporotrichosis can be followed by periodic-acid Schiff (PAS) and Grocott's methenamine silver (GMS) method.

  • Further laboratory studies (eg, tuberculosis test, antinuclear antibody test) may be needed to identify other potential infectious or noninfectious causes that may mimic sporotrichosis.

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Imaging Studies

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  • If primary pulmonary sporotrichosis is suspected, chest radiography may be helpful.

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Other Tests

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  • Immunoelectrophoresis and agglutination techniques are available in the serodiagnosis of this mycosis. A limitation of these tests, however, is their lack of sensitivity in diagnosing cutaneous sporotrichosis.

  • An enzyme-linked immunosorbent assay (ELISA) has been developed for specific antibody detection in serum specimens of patients with sporotrichosis, which has shown to have higher sensitivity; however, cross-reactions between S schenckii and Leishmania have been reported when using ELISA.

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Procedures

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  • Diagnosis must often await the results of tissue culture. Despite the usual difficulty in visualizing S schenckii yeast cells on routine hematoxylin and eosin (H&E) stains, the organism is usually cultured relatively easily. A punch biopsy or incisional biopsy may provide the best sample for these 2 tests. When tissue is obtained for culture, submit the specimen in (nonbacteriostatic) normal saline to the laboratory without delay.

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Histologic Findings

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  • S schenckii is often very difficult to recognize in regular H&E tissue sections or even when tissue is stained with PAS or GMS. The cigar-shaped yeast cells are usually quite sparse within the tissue. Although geographic differences have been reported in the abundance of S schenckii found in the tissues, as have differences in the ease of identifying them with special stains, the reasons for these differences are unknown.

  • Because these yeast cells are usually difficult to find in the tissue, seeking clues to their presence may increase the likelihood of finding the organism.

  • From a low-power view, the tissue often manifests a pseudoepitheliomatous hyperplasia with microabscess formation. This is a nonspecific finding but is often a clue to deep fungal infection, prompting the investigator to make a close survey of the tissue for infective organisms.

  • A diffuse, mixed, inflammatory cell infiltrate is often found throughout the dermis, extending into the subcutaneous fat. When found, the yeast often resides within microabscesses or within macrophages and giant cells.

  • Asteroid bodies may also be a clue to sporotrichosis. These entities are eosinophilic round bodies with pink material radiating outward from their center. Asteroid bodies most likely form as a result of accumulation of immunoglobulins surrounding a yeast cell.

  • A fluorescent antibody technique may enhance diagnostic specificity. This technique uses anti-Sporothrix immunoglobulins labeled with fluorescein dye to enhance identification of the yeast cells in tissue.

  • Fortunately, even if the fungus cannot be observed in the tissues, it is often very easy to grow in culture.

  • One case reported a histology mimicking that of cutaneous cryptococcosis. [13]

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