Stains & CD markers
GMS

Deputy Editor-in-Chief: Patricia Tsang, M.D., M.B.A.
Fang Zhou, M.D.

Topic Completed: 7 May 2021

Minor changes: 18 June 2021

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PubMed Search: Gomori methenamine silver "last 5 years"[dp]

Fang Zhou, M.D.
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Cite this page: Zhou F. GMS. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/stainsgms.html. Accessed September 21st, 2021.
Definition / general
  • Grocott-Gomori methenamine silver (GMS) is a special stain to detect fungi
  • Also positive in some nonfungal organisms and nonorganisms
Essential features
  • Outlines fungal organisms by staining polysaccharides in cell walls
  • Fungal morphology on GMS usually not specific enough to allow definitive species identification
  • Stains some nonfungal organisms: bacteria, mycobacteria, Strongyloides, viral inclusions
  • Artifacts, mimickers and other pigments are common confounders to accurate interpretation
Terminology
  • Other names for GMS:
    • Grocott stain
    • Grocott methenamine (hexamine) silver stain
  • Disambiguation from other similar terms:
Pathophysiology
Clinical features
  • GMS stain cannot provide definitive organism identification
  • Identification is preferably by other methods:
    • Culture (which can also gather susceptibility data)
    • Alternative testing of nontissue samples (e.g. antibody detection, antigen detection, galactomannan, β-D-glucan, PCR, blood culture, etc.)
    • Molecular testing
      • Few clinically validated tests are available for testing of formalin fixed, paraffin embedded (FFPE) blocks
      • Many false negatives due to formalin crosslinking
    • In a few instances, additional special stains on formalin fixed, paraffin embedded (FFPE) blocks
  • Reference: Clin Microbiol Rev 2011;24:247
Interpretation
  • Sharply outlines fungal cell walls
  • Gray to black with peripheral outlines
  • Organisms may be very few and pale
  • Artifacts are common
    • Irregular sizes and shapes
    • No peripheral outline
    • Not associated with tissue reaction
    • Out of tissue plane
  • Counterstain: light green
    • Can also use light H&E (e.g. when a case sent for consult contains only one unstained slide)
  • Signs of infection: inflammation with or without granulomas, necrosis, hemorrhage, angioinvasion
  • Otherwise, it may be colonization rather than true infection; clinical correlation is required
  • In comment, describe the fungal elements seen on GMS
    • Hyphae: Septated or nonseptated? Branching or nonbranching? Acute or right angle branching?
    • Yeasts: Budding or nonbudding? Broad based or narrow based budding?
    • Presence of spherules or endospores
  • If a fungal identity in the report is requested by clinician, then state the fungi most frequently associated with this morphology and that morphologic mimickers exist; include a statement about the importance of clinical correlation
  • Reference: Clin Microbiol Rev 2011;24:247
Uses by pathologists
  • GMS is ordered when fungi are suspected on H&E or cytology preparations
    • Granulomatous reaction is most common
    • Wide range of other reactions: exudative, necrotic or little cellular response (immunocompromised)
    • On H&E and cytologic preparations, fungi can be stained at varying intensities, appear refractile (capsule) or may not be visible
    • More than one organism may be identified in the same lesion
  • Advantages
    • Relatively quick and cost effective
    • GMS positive fungus in tissue helps confirm a positive culture result for environmentally ubiquitous fungi (versus contaminant)
    • Culture may be false negative
    • Pneumocystis cannot be grown in culture (mBio 2018;9:e00939)
    • Antibody testing can be negative in immunodeficient patients
    • Antibody and antigen tests may crossreact between different organisms
  • Disadvantages
    • Low sensitivity
    • Cannot definitively identify fungal species
    • Cannot provide antifungal susceptibility data
Microscopic (histologic) images

Contributed by Fang Zhou, M.D.

Positive staining: normal
Keratin debris

Keratin debris

Cytoplasmic mucin, peribronchial glands Cytoplasmic mucin, peribronchial glands

Cytoplasmic mucin, peribronchial glands

Cytoplasmic mucin

Cytoplasmic mucin, sinonasal mucosa

Thin extracellular mucin

Thin extracellular mucin


Thick extracellular mucin

Thick extracellular mucin

Neutrophil cytoplasm

Neutrophil cytoplasm

Foreign bodies near fungus

Foreign bodies near fungus

Artifacts out of plane Artifacts out of plane

Artifacts out of plane


Polarizable foreign fibers Polarizable foreign fibers

Polarizable foreign fibers

Polarizable foreign fibers Polarizable foreign fibers

Polarizable foreign fibers



Positive staining: fungal organisms
Fungal hyphae

Fungal hyphae

Fungal yeasts Fungal yeasts

Fungal yeasts

Keratin debris

Fungal pseudohyphae and yeasts


Probable <i>Cryptococcus</i> spp. Probable <i>Cryptococcus</i> spp.

Probable Cryptococcus spp.

Probable <i>Cryptococcus</i> spp. Probable <i>Cryptococcus</i> spp.

Probable Cryptococcus spp.



Positive staining: nonfungal organisms
Gram positive coccal bacteria Gram positive coccal bacteria

Gram positive coccal bacteria

Gram positive coccal bacteria Gram positive coccal bacteria

Gram positive coccal bacteria


Filamentous bacteria

Filamentous bacteria

Mycobacteria Mycobacteria

Mycobacteria



Other confounding pigments
Calcium phosphate deposits Calcium phosphate deposits

Calcium phosphate deposits

Melanin pigment Melanin pigment

Melanin pigment

Anthracotic pigment Anthracotic pigment

Anthracotic pigment



Contributed by Andrey Bychkov, M.D., Ph.D. and Jijgee Munkhdelger, M.D., Ph.D.

Candida esophagitis

Esophagitis

Virtual slides

Images hosted on other servers:

Invasive aspergillosis, sinonasal

Deep fungal infection, skin

Fungal dermatitis

Positive staining - normal
Positive staining - disease
  • Fungal yeasts (diameter 2 - 15 microns) (Clin Microbiol Rev 2011;24:247)
    • Blastomyces dermatitidis
    • Cryptococcus spp.
    • Histoplasma capsulatum
    • Candida glabrata: yeasts only (other Candida spp. show mixed yeasts and pseudohyphae)
    • Pneumocystis jirovecii: will not grow in culture
    • Penicillium marneffei
    • Paracoccidioides brasiliensis
    • Sporothrix schenckii
    • Emmonsia crescens
    • Lacazia loboi
    • Other emerging opportunistic fungi, etc.
  • Fungal hyphae (diameter 2 - 6 microns) (Clin Microbiol Rev 2011;24:247)
    • Often ubiquitous in the environment (especially soil) and can contaminate cultures, so seeing hyphae in infected tissue is helpful to confirm culture results (Clin Microbiol Rev 2011;24:247)
    • Aspergillus spp.
    • Mucorales order: stains poorly with GMS; add PAS stain
      • Mucor spp. and Rhizopus spp. (mucormycosis / zygomycosis)
      • Entomophthorales spp.
    • Dematiaceous (melanin+) fungi
      • Madurella spp., Fonsecaea spp., Cladophialophora spp., Exophiala spp., Curvularia spp., Bipolaris spp., etc.
    • Other hyphae seen in tissue infections: Trichosporon spp., Fusarium spp., Scedosporium spp., Trichoderma spp., Paecilomyces spp., Pseudoallescheria spp., Scopulariopsis spp., Acremonium spp., Schizophyllum spp., Phaeoacremonium spp., Trichophyton spp., Phialophora verrucosa, Bipolaris spicifera, Curvularia lunata, etc. (other emerging opportunistic fungi)
  • Mixture of fungal yeasts and pseudohyphae:
  • Mixture of fungal spherules and endospores:
  • Nonfungal organisms (J Am Soc Cytopathol 2017;6:223, Diagn Cytopathol 2017;45:1105, Suvarna: Bancroft's Theory and Practice of Histological Techniques, 8th Edition, 2019, Clin Microbiol Rev 2011;24:247)
    • Must tell them apart from fungi (use size, shape)
    • May be helpful in challenging or sparse cases to prompt the ordering of additional validated confirmatory stains or clinical tests for the nonfungal organisms
      • In absence of other confirmatory results, interpret the GMS with caution (contaminants, artifacts, mimickers)
    • Mycobacterium
      • Fatty capsule may be lost due to antimycobacterial therapy and tissue processing, causing acid fast stains to fail or stain fewer bacilli
      • Sometimes, GMS can still stain residual cell wall carbohydrates
    • Bacteria (Gram stain may be lost due to necrosis or antibiotics)
      • Streptococcus spp.
      • Staphylococcus spp.
      • Filamentous: Nocardia and Actinomyces spp.
      • Bacillus cereus
      • Bartonella henselae
      • Bartonella quintana
    • Strongyloides stercoralis
    • Schistosoma eggs
    • Cytomegalovirus inclusions
    • Toxoplasma
Negative staining
  • Organisms mimicking fungi that are GMS negative (Clin Microbiol Rev 2011;24:247)
    • Rhinosporidium seeberi
    • Trypanosoma cruzi
    • Leishmania spp.
  • Nonorganisms (may resemble fungi on H&E but do not contain carbohydrates and are negative for GMS)
Sample pathology report
  • Sinonasal mucosa, biopsy:
    • Invasive fungal sinusitis (see comment)
    • Comment: GMS stain on block A1 shows broad, nonseptate fungal hyphae with right angle branching, associated with tissue necrosis and angioinvasion, consistent with invasive fungal sinusitis. Dr. _ was notified at 10:00am on 4/19/2021 with repeat back verification.
Board review style question #1

GMS stain performed on an esophageal biopsy from a patient with AIDS shows a mixture of yeasts and pseudohyphae, suggestive of Candida species. Which species can be ruled out based on this morphology?

  1. Candida albicans
  2. Candida dubliniensis
  3. Candida glabrata
  4. Candida parapsilosis
  5. Candida tropicalis
Board review style answer #1
C. Candida glabrata, formerly known as Torulopsis glabrata, is the only Candida species that does not form pseudohyphae in tissue. It was formerly considered a saprophytic organism that is commonly found in normal human flora but it has emerged as an opportunistic organism with both innate and acquired antifungal resistance (Microorganisms 2019;7:39, J Clin Microbiol 2004;42:4419).

Comment Here

Reference: GMS
Board review style question #2
A biopsy from a solid lung nodule shows granulomatous inflammation and fungal hyphae are seen on GMS stain. Which of the following is the most likely causative organism?

  1. Blastomyces dermatitidis
  2. Cryptococcus spp.
  3. Histoplasma capsulatum
  4. Pneumocystis jirovecii
  5. Scedosporium spp.
Board review style answer #2
E. Among the listed organisms, only Scedosporium spp. (though uncommon) are usually encountered as hyphae in infected tissue specimens (Clin Microbiol Rev 2008;21:157). It is an opportunistic fungus with intrinsic antifungal resistance (Med Mycol 2018;56:102). The other organisms in the answer choices are more commonly encountered dimorphic fungi that are usually seen as yeast forms in infected tissues.

Comment Here

Reference: GMS
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