Noncandidal Fungal Infections of the Mouth Workup

Updated: Mar 01, 2018
  • Author: Manuel Valdebran, MD; Chief Editor: William D James, MD  more...
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Workup

Laboratory Studies

Tests can include cytology smears; biopsy and staining with PAS or Gomori methenamine silver stain; cultures; DNA probing, which is becoming increasingly available but at present is not sufficient alone; and, in some circumstances, serodiagnosis, which is available for aspergillosis (galactomannan antigen testing) and cryptococcosis (capsular polysaccharide antigen testing). However, serodiagnosis is not adequate without the other tests mentioned, which are confirmatory tests.

General laboratory testing can include the following:

  • Comprehensive metabolic panel (eg, to evaluate for diabetes or malnutrition)

  • CBC count with differential (eg, to evaluate for neutropenia or lymphopenia)

  • HIV serostatus testing

  • Immunologic testing

The diagnosis of aspergillosis is confirmed by smear results and lesional microscopy findings. Staining with PAS or Gomori methenamine silver shows regular, narrow (4 µm wide), branching, and septate hyphae of Aspergillus species. However, hyphae of Fusarium species, Mucor species, and Pseudallescheria boydii may cause confusion. Immunostains may help for definitive diagnosis. Culture of tissue or fluids on Sabouraud or Mycosel agar may return positive results, but this is not invariable. Furthermore, the organisms are ubiquitous; therefore, isolation of Aspergillus organisms is not proof of disease. Estimations of serum precipitin and immunoglobulin E–specific antibody levels may support the diagnosis.

The diagnosis of blastomycosis is based on smear or culture results. Biopsy may show Blastomyces species in the tissue, with granulomas. Staining with PAS, methenamine silver nitrate, or Fontana-Masson stain helps in the identification. The organism can be mistaken for H capsulatum, C neoformans, Bipolaris species, or Wangiella dermatitidis. Direct immunostaining is the most useful means of confirmation. DNA probes can yield an answer in 2 hours. Skin test and serology results are, unfortunately, unreliable, although serotesting has improved.

Coccidioidomycosis is diagnosed mainly by means of a thorough history and physical examination supported by histology findings that show granulomas with spherules containing endospores. DNA probes are now available. Also helpful are serology and the Spherulin or coccidioidin skin tests. Culture, although useful, is potentially hazardous to laboratory staff.

Cryptococcosis is confirmed by microscopy or by staining with PAS, mucicarmine, or methenamine silver stain. The stains show granulomas. Smears may also be stained with India ink or nigrosin. The yeast cell is round or elliptical, 4-6 µm in diameter, clear, and capsulated. It also fluoresces in ultraviolet light. Culture and assay of serum or cerebrospinal fluid for capsular antigen and antibody (latex agglutination test) may help in diagnosis.

Histoplasmosis is confirmed with microscopy, which shows granulomas with PAS-positive spores with a narrow halo in macrophages and microabscesses with necrosis. DNA probes are now available. Culture results on Sabouraud agar are also confirmatory. Complement fixation tests may be of value; a titer greater than 1:32 indicates infection, but several other serological tests are also available. The histoplasmin skin test result is of little importance in diagnosis.

A diagnosis of mucormycosis is confirmed with smears or the histologic demonstration of tissue invasion by broad (5-50 µm), irregularly wide, nonseptate, branching hyphae. These hyphae characteristically invade blood vessels and cause thrombosis, ischemia, infarction, and necrosis. Methenamine silver or PAS staining is best to show the fungi, which are difficult to culture from a swab sample.

Paracoccidioidomycosis is diagnosed using pus or scrapings from a lesion. Examined in potassium hydroxide, the samples may show the rounded, refractive cells of P brasiliensis, which have characteristic multiple budding. Biopsy is required for definitive diagnosis; it reveals suppurative granulomas with giant cells and blastospores, which are double-contoured, cystlike structures approximately 30 µm in diameter. These are often surrounded by daughter spores (Mickey Mouse appearance). Methenamine silver nitrate or PAS stain is particularly useful to demonstrate the organisms, and direct immunostaining with Blastomyces antiserum is less frequently used.

Cytological examination, although rapid and available, [39] is usually complemented by other investigations. Smear or culture can also be diagnostically useful, but P brasiliensis grows extremely slowly. Serologic examination by means of immunodiffusion, or particularly complement fixation, is useful in epidemiologic studies. Reliable skin tests are not available.

For the diagnosis of geotrichosis, direct examination may provide a rapid diagnosis when multiple hyphae and conidia are present. However, conidia may have features similar to those of Candida species. Therefore, cultures are preferred to establish an accurate diagnosis, ands they present as white, membranous, villous, wet colonies showing multiple rectangular conidia under the microscope. [22]

For Rhodotorula infections, Gram staining demonstrates a gram-positive yeast with a thin capsule on India ink. Cultures show a coral-pink, moist-to-mucoid yeast-like appearance. They differ from Candida species by producing pink-to-red colonies, owing to its inability to ferment sugars and the lack of pseudohyphae. [37]

Histological findings of hyaline and septate filaments that dichotomize at right angles  may resemble those of Aspergillus; therefore, cultures are essential in the diagnosis of Fusarium infection. Microscopic visualization from cultures shows fusoid banana-shaped multicellular macroconidia with foot cells at the base. [25, 38]

Chromogenic culture media such as CHROMagar Candida® can be used to identify these species. Finally, molecular biology can be used distinguish between G candidum and G capitatum. [22]

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Imaging Studies

Imaging studies can include chest radiography and plain radiography, CT scanning, or MRI to evaluate the submucosal extent, especially if the palate is involved.

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Procedures

Incisional biopsy with special stains (eg, PAS, methenamine silver) and cytologic smears can be performed.

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