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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_182_библиотеки_им_акад_М_И_Перельмана.pdf
ASPERGILLOSIS
Aspergillus fruiting bodies are seen in this cell block
(from an FNA) from a patient with chronic pulmonary
aspergillosis. Although rare in human infection, the forms
appear in chronic disease.
Fungal Infections: Morphological Diagnosis of Fungal Infections
TERMINOLOGY
Definitions
Latin: "Aspergillum" (a liturgical instrument to sprinkle
holy water)
Aspergillosis: Infection caused by Aspergillus species
ETIOLOGY/PATHOGENESIS
Infectious Agents
Member of the phylum Ascomycota
Ubiquitous species in environment
> 180 known species, ~ 20 of which are known to be
harmful to humans and other animals
Most common species of clinical significance:
Aspergillus fumigatus, followed by Aspergillus flavus,
Aspergillus niger, Aspergillus terreus
Reproduce asexually by producing unbranched chains
of conidia from a bulbous structure called a vesicle
(fruiting body)
CLINICAL ISSUES
Presentation
Pulmonary aspergillosis
Allergic bronchopulmonary aspergillosis (ABPA)
Hypersensitivity reaction to Aspergillus spp.
A. fumigatus is the most common etiologic agent
Primarily in patients with cystic fibrosis or steroid-
dependent asthma
Characterized by mucoid impaction of bronchi,
eosinophilic pneumonia, and bronchocentric
granulomatosis; patients can be asymptomatic in
early stage with only infiltrates on chest x-rays
Disease is irreversible once patient has reached
III
1
fibrotic stage
Aspergillus spp. are cultured from sputum in up to
2/3 of patients with ABPA
PAS lung section shows acutely branched septate hyphae.
Terminal swellings , which mimic yeast forms, are
present. Culture shows Aspergillus fumigatus and no
isolation of yeast.
Good response to steroids
Tracheobronchitis: Risk factors include solid organ
transplant, hematologic malignancies, HIV infection
Chronic pulmonary aspergillosis
Evolves slowly; duration of disease is usually
longer than 3 months
Most common sign is hemoptysis, but some
patients can be asymptomatic
Spectrum of chronic pulmonary aspergillosis
Aspergilloma: Fungus ball with Aspergillus hyphae,
fibrin, and cellular debris within a pulmonary
cavity
Chronic cavitary pulmonary aspergillosis:
Formation and expansion of 1 or more pulmonary
cavities over months
Chronic fibrosing pulmonary aspergillosis: Disease
progression to marked and extensive lung fibrosis
Chronic necrotizing pulmonary aspergillosis:
Usually associated with immunocompromised
states, e.g., diabetes, HIV infection, advanced age,
chronic steroid use, malnutrition
Invasive (systemic/disseminated) aspergillosis
Mostly in severely immunocompromised patients
Endophthalmitis may be a presenting feature
Relapsed invasive aspergillosis
Risk factors: Prolonged neutropenia, no remission
of underlying hematologic malignancy, use of
systemic glucocorticoids
Rhinosinusitis: Infection of paranasal sinuses
Endocarditis
Second to Candida spp. as a cause of fungal
endocarditis
Primarily seen in intravenous drug users or in
patients with prosthetic heart valves or indwelling
central venous catheters
Blood cultures are rarely positive
Cutaneous aspergillosis
Primarily from direct inoculation in setting of
trauma, e.g., burn victims
2
ASPERGILLOSIS
Etiology
Most common species of clinical significance includes
A. fumigatus, followed by A. flavus, A. niger, A. terreus
Imaging Findings
Invasive lung infection can manifest on CT scan
as a lung nodule with halo sign (ground-glass
opacity surrounding nodule) or air crescent sign that
occurs when there is fungal vascular invasion and
hemorrhage
Microscopic Pathology
Septate hyphae (3-6 m in diameter)
Dichotomous branching at 45 angles
Tend to grow radially from hematogenous lesions in
tissue
Gastrointestinal aspergillosis: Relatively rare, but risk
factors include neutropenia, receipt of glucocorticoids,
and mucosal breakdown
Central nervous system involvement
Occur in setting of disseminated infection or from
local extension from paranasal sinuses
Mycotic aneurysms develop in some cases and can
rupture, resulting in a hemorrhagic cerebrovascular
accident, subarachnoid hemorrhage, &/or empyema
formation
Treatment
Azoles, polyenes, and echinocandins are classes of
antifungals that can be used
Choice of drugs depends on clinical response, presence
of antifungal resistance, drug interaction with
chemotherapeutic regimens, and patient’s tolerance of
drugs
Initial therapy
Usually a combination of voriconazole and an
echinocandin; monotherapy with voriconazole has
also been used
Amphotericin B is preferred in cases of azole
intolerance, in patients who have recently received
azoles, or as empiric treatment in patients who have
suspected invasive mucormycosis or aspergillosis
before definitive diagnosis is made
Salvage therapy
For patients who do not respond to initial therapy
Combination of antifungals are used depending on
clinical response
Surgical debridement or resection: Helpful in cases in
which drugs cannot be delivered to large symptomatic
lesions or when there is an imminent threat to vessels
Allergic bronchopulmonary aspergillosis: Oral steroids
are needed usually for a prolonged period of time
Prognosis
Invasive aspergillosis carries a poor prognosis
Successful treatment depends on site of lesion and
immune status of host
Key Facts
Acute inflammation is often present in invasive
disease; lesions show little inflammatory reaction in
neutropenic patients
Angioinvasion is commonly present in invasive
disease
Ancillary Tests
Hyphae highlighted by periodic acid-Schiff and
fungal silver stains
Cases of invasive aspergillosis generally show serum
positivity of galactomannan and 1,3--D-glucan
Top Differential Diagnoses
Candidiasis
Mucormycosis
Hyalohyphomycosis
Concurrent infections with other fungi
IMAGE FINDINGS
Radiographic Findings
Invasive lung infection can manifest on CT scan as a
lung nodule with
MICROSCOPIC PATHOLOGY
Histologic Features
Septate hyphae (3-6 m in diameter) with acute-angle
branching at 45
Tend to grow from hematogenous lesions in tissues in
radial fashion (especially when infarcted/necrotic)
Vesicles with conidia ("fruiting bodies") can be
observed when fungi are in oxygenated areas such as
cavitary lung lesions or paranasal sinuses
Terminal swellings of hyphae may be present in
oxygenated areas (mimicking yeast)
Presence of dark brown or black pigments may be
present in infection caused by A. niger, which produces
pigmented conidiospores
Invasive diseases
Halo sign: Ground-glass opacity surrounding nodule
Not specific for aspergillosis
Can also be seen with neoplasia, infections caused
by other fungi or bacteria such as Pseudomonas
aeruginosa or mycobacteria
Air crescent sign when there is fungal vascular
invasion and hemorrhage
This finding, however, is not specific and can be
seen with dematiaceous fungi; therefore, correlation
with clinical, culture, and molecular findings is
needed
Acute inflammation with neutrophils and necrotic
debris; little inflammatory reaction in neutropenic
patients
Angioinvasion is commonly present, resulting
in thrombosis, hemorrhagic lesions and tissue
infarction
Fungal Infections: Morphological Diagnosis of Fungal Infections
III
1
3
ASPERGILLOSIS
Granulomatous response may be present
occasionally
Calcium oxalate crystalloids can be present if
primary lesion is longstanding
Allergic or hypersensitivity aspergillosis
Hypersecretion of mucus with neutrophils and
eosinophils
Charcot-Leyden crystals are sometimes seen
Aspergillomas
Fungus destroys lung tissue, forming a cavity in
which a fungus ball (aspergilloma) can be produced
Cavity wall may contain inflammatory granulation
tissue, fibrous tissue, granulomas, eosinophils or
eosinophilic material
Calcium oxalate crystalloids, hemorrhage or
hemosiderin-laden macrophages can be present
ANCILLARY TESTS
Histochemistry
Hyphae highlighted by silver stains (Gomori
methenamine silver [GMS] or methenamine silver
Fungal Infections: Morphological Diagnosis of Fungal Infections
III
[MSS] and periodic acidSchiff [PAS])
PCR
Mixed results in terms of sensitivity and specificity
Systemic review and meta-analysis suggested that
sensitivity and specificity of PCR to detect invasive
aspergillosis was 88% and 75%, respectively
Serological Immunoassays
Galactomannan
Galactomannan antigen is present on cell walls of
Aspergillus spp.
Immunoassay approved by the FDA for use only
on serum and bronchoalveolar lavage fluid, but
galactomannan can also be detected in other
samples, e.g., pleural fluid and cerebrospinal fluid
Positive in serum in patients with invasive
aspergillosis
Assay sensitivities: 40-100%; specificities: 56-100%
Sensitivity of serum detection decreased by
concomitant administration of antifungal drugs
Can be detected in serum before presence of clinical
symptoms in some patients
Other fungi can produce positive results due to
presence of galactomannans or polysaccharides
containing galactofuranose residues on their cell
walls
e.g., Penicillium, Paecilomyces, Alternaria, and
Histoplasma, hence correlation with clinical,
culture, and histologic findings is needed
False-positive results have been reported in the
following settings
Patients receiving certain -lactam antibiotics,
e.g., intravenous piperacillin-tazobactam, due
to presence of galactomannan or cross-reactive
antigen in antibiotic formulations
Contamination of foods with Aspergillus spp. or
closely related fungi, such as Penicillium spp.
Patients receiving transfusions of blood
products that are collected in bags containing
galactomannan antigen
Serial testing of sera helps to determine whether
patient has invasive disease, is responding to
treatment, or is merely colonized with Aspergillus
spp.
Serum galactomannan level at time of diagnosis and
the 1-week galactomannan decay were found to be
predictive of all-cause mortality in cases of invasive
aspergillosis
1,3--D-glucan
Cell wall component of many fungi
Positive in serum in patients with invasive
aspergillosis
Not specific for aspergillosis; can be detected in
patients with other invasive fungal infection, e.g.,
candidiasis, infection of Pneumocystis jirovecii
Typically negative in patients with mucormycosis or
cryptococcosis
False-positive results have been reported in the
following settings
Patients receiving intravenous immunoglobulin
or blood products filtered through cellulose filters
containing -D-glucan antigen
Hemodialysis with cellulose membranes
Patients with serosal exposure to gauze packs
containing -D-glucan
Aspergillus antibodies (precipitins)
Allergic bronchopulmonary aspergillosis: Elevated
serum IgE and IgG antibodies specific to Aspergillus
spp. can be detected
Total serum IgE is also elevated
Chronic pulmonary aspergillosis: Elevated specific
IgG detected in most cases and elevated specific IgE
detected in ~ 50% of cases; however, standardization
of this testing is not well established for this
indication
No role in diagnosis of invasive aspergillosis
Skin Test
In cases of allergic aspergillosis, positive skin reactivity
to Aspergillus antigens can be detected
Cultures
Cultures from bronchoalveolar fluids may reflect
colonization and not actual infection
Blood cultures are positive in ~ 5% of invasive cases
Positive culture from a normally sterile site, or
positive culture in combination with presence of
tissue invasion provides good evidence of invasive
aspergillosis
Other Assays in Development
Lateral flow device (LFD) that detects an extracellular
antigen secreted by Aspergillus spp. using a
monoclonal JF5 antibody has been approved for use in
Europe
Detection of secondary metabolites in human breath
using thermal desorption-gas chromatography/mass
spectrometry
1
4
ASPERGILLOSIS
DIFFERENTIAL DIAGNOSIS
Candidiasis
Aspergillus spp. are distinguished by presence of
dichotomous branching at acute angles
Hyphae of Aspergillus spp. may be mistaken for
nonbudding yeast cells when cut transversely
When exposed to oxygen, Aspergillus hyphae may
produce terminal swellings, mimicking yeast forms
Candida spp. are positive by Gram stain, while
Aspergillus spp. are negative
Correlation with culture and molecular findings is
needed when histochemical findings are equivocal
Mucormycosis
Angioinvasion is commonly present in invasive
disease of mucormycosis and aspergillosis
Mucorales exhibit few septations and right-angle
branching
Serum galactomannan and -D-glucan are typically
negative in invasive mucormycosis, while they are
usually positive in cases of invasive aspergillosis
Hyalohyphomycosis
Fusarium, Penicillium spp., and other hyaline
septate molds like dermatophytes may present as
dichotomous fungi similar to Aspergillus spp.
Aspergillus spp. can be distinguished by presence of
fruiting heads, but these are usually present only in
well-oxygenated lesions or cavities
Correlation with culture or molecular findings is
needed for definitive classification
Concurrent Infections With Other Fungi
Concurrent infection with Aspergillus spp., Candida
spp. or Mucor spp. have been reported
Alternative diagnostic testing of tissues, such as
immunohistochemistry, in situ hybridization, or PCR,
may be needed for definitive classification
DIAGNOSTIC CHECKLIST
Clinically Relevant Pathologic Features
Usually opportunistic invaders
Cultures from bronchoalveolar fluids may reflect
colonization and not actual infection
Positive culture in combination with presence of tissue
invasion or positive culture from a normally sterile site
provides good evidence of invasive aspergillosis
Pathologic Interpretation Pearls
Septate hyphae (3-6 m in diameter) with
dichotomous branching at 45 angles
Tend to grow radially from hematogenous lesions in
tissue
In invasive disease, angioinvasion by hyphae produces
necrosis or hemorrhage of surrounding tissue; degree
of inflammation can be minimal in neutropenic
patients
Correlation with clinical, culture, and molecular
findings is needed to make definitive diagnosis when
histologic findings are equivocal
SELECTED REFERENCES
1. Schuetz AN: Invasive fungal infections: biomarkers
and molecular approaches to diagnosis. Clin Lab Med.
33(3):505-25, 2013
2.
Martn-Rabadn P et al: False-positive Aspergillus
antigenemia due to blood product conditioning fluids.
Clin Infect Dis. 55(4):e22-7, 2012
3. Baxter CG et al: Pulmonary aspergillosis: an alternative
diagnosis to lung cancer after positive [18F]FDG positron
emission tomography. Thorax. 66(7):638-40, 2011
4. Guarner J et al: Histopathologic diagnosis of fungal
infections in the 21st century. Clin Microbiol Rev.
24(2):247-80, 2011
5. Koo S et al: Prognostic features of galactomannan
antigenemia in galactomannan-positive invasive
aspergillosis. J Clin Microbiol. 2010 Apr;48(4):1255-60.
Epub 2010 Feb 10. Erratum in: J Clin Microbiol.
48(5):1994, 2010
6. Lee S et al: Discrepancy between histology and culture in
filamentous fungal infections. Med Mycol. 48(6):886-8,
2010
7. Sherif R et al: Pulmonary aspergillosis: clinical
presentation, diagnostic tests, management and
complications. Curr Opin Pulm Med. 16(3):242-50, 2010
8. Marty FM et al: Role of (1-->3)-beta-D-glucan in the
diagnosis of invasive aspergillosis. Med Mycol. 47 Suppl
1:S233-40, 2009
9. Maschmeyer G et al: Invasive mould infections: a multidisciplinary update. Med Mycol. 47(6):571-83, 2009
10. Mengoli C et al: Use of PCR for diagnosis of invasive
aspergillosis: systematic review and meta-analysis. Lancet
Infect Dis. 9(2):89-96, 2009
11. Riscili BP et al: Noninvasive pulmonary Aspergillus
infections. Clin Chest Med. 30(2):315-35, vii, 2009
12. Wheat LJ: Approach to the diagnosis of invasive
aspergillosis and candidiasis. Clin Chest Med. 30(2):367-77,
viii, 2009
13. Sipsas NV et al: Clinical issues regarding relapsing
aspergillosis and the efficacy of secondary antifungal
prophylaxis in patients with hematological malignancies.
Clin Infect Dis. 42(11):1584-91, 2006
14. Marr KA et al: Antifungal therapy decreases sensitivity of
the Aspergillus galactomannan enzyme immunoassay. Clin
Infect Dis. 40(12):1762-9, 2005
15. Klont RR et al: Utility of Aspergillus antigen detection in
specimens other than serum specimens. Clin Infect Dis.
39(10):1467-74, 2004
16. Walsh TJ et al: Detection of galactomannan antigenemia in
patients receiving piperacillin-tazobactam and correlations
between in vitro, in vivo, and clinical properties of the
drug-antigen interaction. J Clin Microbiol. 42(10):4744-8,
2004
Fungal Infections: Morphological Diagnosis of Fungal Infections
III
1
5
Radiologic and Microscopic Features
g
A
p
A
A
A
(Left) Chest CT scan of lungs
shows the presence of an
irregular nodule surrounded by
round-glass opacity ("halo"
sign) . Biopsy and ancillary
testing confirms the presence
of an aspergilloma. (Right)
gross lung section shows
a nodular lesion , which
on subsequent histologic
examination demonstrated
a focus of aspergillosis
surrounded by infarcted tissue.
Disseminated aspergillosis
often produces hemorrhagic
lesions at any site due to blood
vessel invasion.
Fungal Infections: Morphological Diagnosis of Fungal Infections
(Left) Septate hyphae with
acute angle-branching
consistent with Aspergillus
spp. as seen on PAS stain
fill the vessel and invade
into surrounding lung tissue
causing infarction. Transverse
cuts of the hyphae mimic
yeasts such as Candida spp.,
which should stain positive on
Gram stain. (Right) Numerous
fungal hyphae causing
infarction and hemorrhage in
lung tissue. Narrow hyphae
are shown with septa and
acute-angle branching
favors Aspergillus being the
etiologic agent.
ASPERGILLOSIS
(Left) Narrow septate
hyphae with acuteangle branching are
resent in a bronchoalveolar
lavage (ThinPrep). Culture
confirms the presence of
spergillus fumigatus. (Right)
spergilloma on PAS stain in a
nasal biopsy shows SplendoreHoeppli phenomenon.
Presence of calcium oxalate
and pigments suggest
. niger, which is confirmed by
culture findings. Several fungi
in the differential diagnosis
may also be pigmented;
therefore, culture or molecular
testing is key.
III
1
6
Variant Microscopic Features
A
A
A
ASPERGILLOSIS
(Left) Tissue section shows
necrosis associated with
large hyphal forms
collection of calcium oxalate
crystals
spergillus spp. (Right)
Tissue section shows hyphal
forms and collections
of Aspergillus-associated
calcium oxalate crystals
microscopy.
, consistent with
under polarized light
and
Fungal Infections: Morphological Diagnosis of Fungal Infections
(Left) High-magnification
GMS-stained
bronchoalveolar lavage (cell
block preparation) shows
hyphae with acute-angle
branching and septa .
Other fungi, e.g., agents
of hyalohyphomycosis,
may be indistinguishable
from Aspergillus in this
setting. (Right) Medium
magnification of a GMSstained tissue biopsy shows
necrosis and Aspergillus spp.
with thick and ribbonous
hyphal forms similar to
Mucor spp. Culture of
this sample confirms the
diagnosis of aspergillosis.
(Left) High magnification
of lung tissue section shows
crowding Aspergillus hyphae
with terminal swellings
mimicking yeast forms.
Terminal swellings result
from exposure to oxygen.
lthough Aspergillus spp.
do not produce yeast or
yeast-like elements, other
hyaline fungi may do so.
(Right) High magnification
of a GMS-stained lung tissue
section shows numerous
spergillus hyphae with
terminal swellings , which
may be confused with yeast
forms.
III
1
7
BLASTOMYCOSIS
High magnification of a skin section on H&E stain shows
multiple multinucleate Blastomyces yeast cells. Thick cell
wall as well as broad-based budding at early and late
stage are seen.
Fungal Infections: Morphological Diagnosis of Fungal Infections
TERMINOLOGY
Synonyms
Gilchrist disease
Definitions
Greek: "Blasto" (bud, sprout, embryo) + "myces" (fungi)
ETIOLOGY/PATHOGENESIS
Environmental Exposure
Infection most often occurs via inhalation of
Blastomyces dermatitidis conidia
Conidia convert to yeast phase in tissue
Yeast forms with thick cell wall are more resistant
than conidia forms to phagocytosis and killing
mediated by immune cells
Endemic areas in North America
Southeastern and south central United States
including Mississippi and Ohio River valleys
Midwestern part of United States and Canadian
provinces around Great Lakes
Small area in New York and Canada along St.
Lawrence River
Sporadic cases in North America, e.g., Ontario,
Manitoba, Wisconsin
Cases reported outside of North America: Africa (most
frequent), Central and South America, Mexico, India,
and Middle East
Outbreaks associated with waterways have been
reported
Infectious Agent
B. dermatitidis
Asexual state of Ajellomyces dermatitidis
Exhibits thermal dimorphism: Yeast phase at 37 C
III
and mycelial phase at room temperature
High magnification of this tissue section on GMS stain
shows Blastomyces yeast forms with characteristic broadbased budding and a thick cell wall.
CLINICAL ISSUES
Presentation
Range from subclinical infection to fatal disseminated
disease
Pulmonary infection
Most common site of involvement
Acute pneumonia
Presentation often indistinguishable from acute
bacterial or viral pneumonia
Subset of patients have self-limited disease
Chronic pneumonia
Often presents with mass-like infiltrates
mimicking pulmonary tuberculosis, malignancy,
or other fungal infections such as histoplasmosis
Adult respiratory distress syndrome (ARDS)
Often presents with diffuse bilateral pulmonary
infiltrates
High mortality
Extrapulmonary infection
Occurs more commonly in men than in women
Cutaneous infection
Skin is 2nd most common site of involvement
Can result from direct inoculation of organisms or
B. dermatitidis dissemination from other sites
Typically presents as ulcerative lesions or raised/
crusted verrucous lesions with irregular borders,
grossly mimicking squamous cell carcinoma, basal
cell carcinoma, pyoderma gangrenosum, or giant
keratoacanthoma
Microabscesses are present
Mucosal lesions of nose, mouth, pharynx or
larynx can occur; verrucous lesions can mimic
squamous cell carcinoma
Osseous infection
3rd most common site of involvement
Can involve any bone; vertebrae, pelvis, and
sacrum are most common sites of involvement
1
8
BLASTOMYCOSIS
Terminology
Infection caused by Blastomyces dermatitidis
Etiology
Infection occurs via inhalation of B. dermatitidis
conidia
Endemic areas in North America: Southeastern, south
central, and midwestern USA including Mississippi
and Ohio River valleys, as well as USA and Canadian
provinces around Great Lakes and St. Lawrence River
Clinical Issues
Most common sites: Pulmonary, cutaneous, osseous
infections
No clinical or radiographic features are specific for
blastomycosis
Extension from osteomyelitis to adjacent joint can
cause purulent arthritis
Extension into soft tissue can lead to formation of
abscesses that track through soft tissues, forming
subcutaneous masses at any spinal level and
draining through skin, resulting in a discharging
sinus or ulcer
Vertebral osteomyelitis due to blastomycosis is
frequently complicated by paravertebral or psoas
abscesses
Other sites of involvement
Virtually any organ can be involved
e.g., genitourinary system: Most common sites of
disease are prostate, testicle, and epididymis
e.g., central nervous system (CNS): Uncommon
in immunocompetent hosts and can present
as meningitis, epidural abscess, or intracranial
abscesses
Laboratory Tests
Wet mount preparations
Fresh wet preparations of clinical specimens can be
examined directly for organisms
Calcofluor white fluorochrome staining is useful
when organisms are sparse, as it allows yeast cells to
fluoresce
Potassium hydroxide (KOH) can enhance the
visibility of the yeast organisms by dissolving tissue
materials
Specimens that can be examined clinically include
sputum, bronchoalveolar lavage fluid, pleural fluid,
cerebrospinal fluid, urine, skin scrapings or purulent
material
Antigen testing
Commercial EIA antigen assay is available for testing
bronchoalveolar lavage fluid, CSF, serum, urine
Overall sensitivity: 93%; specificity: 79%
Can be used to follow response to treatment
Cross-reactivity reported in patients with
histoplasmosis, hence simultaneous testing for
Histoplasma should be done
Key Facts
Immunocompromised patients have more aggressive
clinical course
Microscopic Pathology
Spherical multinucleated yeast cells (8-15 m) with
single broad-based budding, thick refractile wall
Pyogranulomatous inflammation
Ancillary Tests
Positive for GMS/MSS, PAS, Congo red stains;
negative for Gram stain and variable for FontanaMasson stain
Top Differential Diagnoses
Coccidioidomycosis
Paracoccidioidosis
Cryptococcosis
Histoplasmosis
Serologic testing
Treatment
Most patients with blastomycosis require therapy,
although some immunocompetent patients with acute
pulmonary infection spontaneously clear infection
and may not need treatment
Pulmonary involvement
Disseminated involvement
CNS involvement: Initial therapy with amphotericin
B, and step-down therapy of voriconazole, which has
good CNS and cerebrospinal fluid penetration
All immunocompromised patients: Therapy with
amphotericin B, followed by step-down therapy of
itraconazole if there is no CNS involvement
Prognosis
ARDS caused by pulmonary blastomycosis is associated
with high mortality
Prognosis worsens when infection spreads beyond
lungs without treatment
Bone disease is more likely to relapse than other forms
of blastomycosis
Cross-reactivity has also been reported in patients
with paracoccidioidomycosis and penicilliosis
Generally not useful for diagnosis in daily practice
Complement fixation and immunodiffusion: Poor
sensitivity and specificity
Radioimmunodiffusion and enzyme immunoassays
(EIAs): Better sensitivity (77-83%) and specificity
(95%) but are not commercially available
Mild to moderate disease: Azole, usually itraconazole
Moderately severe to severe disease: Amphotericin
B; lipid formulation of amphotericin B is preferred
to avoid nephrotoxicity of amphotericin B
deoxycholate
Mild to moderate disease with no CNS involvement
Oral azole, usually itraconazole
Moderately severe to severe with no CNS
involvement
Amphotericin B until improvement is observed,
followed by oral itraconazole
Fungal Infections: Morphological Diagnosis of Fungal Infections
III
1
9
Blastomycosis has been reported to have more
aggressive course and more likely to relapse in
immunocompromised patients
IMAGE FINDINGS
Radiographic Findings
Radiographic features are not specific
Lung involvement
Alveolar or mass-like infiltrates are the most
common findings
Patients with chronic pneumonia more often
present with mass-like infiltrates
Reticulonodular and miliary patterns are less
common and are usually associated with ARDS
Cavitation of lung parenchyma can be seen but is
rare
Radiographic differentials include tuberculosis,
histoplasmosis, and coccidioidomycosis
Bone involvement
Can appear as a clearly demarcated osteolytic lesion
or as a diffuse, destructive process with periosteal
Fungal Infections: Morphological Diagnosis of Fungal Infections
new bone formation
MICROBIOLOGY
Culture
Sabouraud dextrose agar or brain heart infusion agar
B. dermatitidis can take up to 3 weeks to grow or may
not grow at all in culture, depending on the clinical
specimen
Sensitivity varies depending on the sample and may
range from 62-100%
MICROSCOPIC PATHOLOGY
Histologic Features
Spherical yeast cells (8-15 m in diameter) with single
broad-based budding
Smaller yeast forms (2-4 m in diameter) have been
reported in cases of blastomycosis
Thick refractile wall may give appearance of a space
between fungal cell contents and surrounding tissue
on H&E stain
Multiple nuclei of yeast may be seen inside yeast cells
on H&E stain
Associated with pyogranulomatous reaction
Acute infection: Neutrophilic inflammation
predominates and yeast organisms can be detected
easily
Chronic infection: Granulomata, which are usually
noncaseating, may form, and yeast organisms can be
difficult to find
Skin and mucosal specimens
Blastomycosis is often associated with formation of
microabscesses, as well as pseudoepitheliomatous
hyperplasia, which can resemble squamous cell
III
carcinoma
Cases with concomitant presence of neoplasias and
tuberculosis have been reported
1
BLASTOMYCOSIS
ANCILLARY TESTS
Histochemistry
Organisms are positive for Grocott methenamine silver
(GMS) stain and periodic acid-Schiff (PAS) stain
Positive for Congo red stain
Negative for Gram stain and variably positive on
Fontana-Masson stain (~ 50%)
Negative or weakly positive for mucicarmine stain
PCR
PCR-based assays have been tested in culture
specimens and paraffin-embedded tissue, as well
as clinical specimens such as bronchial washings,
bronchoalveolar fluid, pleural fluid, sputum, blood
No cross-reactivity to other fungal DNA has been
reported
Utility still needs to be confirmed in large prospective
studies
Molecular Diagnostics
DNA hybridization
Commercially available chemiluminescent DNA
probe (AccuProbe; Gen-Probe, Inc., San Diego,
CA) that hybridizes to rRNA of B. dermatitidis can
provide rapid results with good sensitivity (> 87%)
and specificity (100%)
Cross-reacts with Paracoccidioides brasiliensis,
as well as rare human pathogens Gymnascella
hyalinospora and Emmonsia parva
DIFFERENTIAL DIAGNOSIS
Candidiasis
Candida spp. can be distinguished from Blastomyces
spp. by their positivity for Gram stain, presence of
pseudohyphae, and lack of broad-based budding
Coccidioidomycosis
Coccidioides spp. usually present as spherules with
multiple endospores
Coccidioides endospores outside spherules, or young
spherules without endospores can be confused with
Blastomyces spp., particularly when 2 spherules abut
one another, mimicking broad-based budding
Examination of serial sections for diagnostic forms
of either fungus may be helpful but not useful when
organisms are sparse in tissue
B. dermatitidis is reported to be weakly positive for
Alcian blue (pH 2.5) and acid-fast stain in a large
proportion of cases whereas Coccidioides immitis/
Coccidioides posadasii are negative for those stains
Paracoccidioidosis
Yeast phase of Paracoccidioides brasiliensis is
distinguished from B. dermatitidis by presence of
multiple, narrow-based buds arranged around
periphery of mother cell, whereas B. dermatitidis
typically present as thick-walled yeast cells with single
broad-based budding
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BLASTOMYCOSIS
Fungal Infections: Morphological Diagnosis of Fungal Infections
Paracoccidioidomycosis occurs almost exclusively in
South America and Central America and is rarely seen
in United States
Cryptococcosis
Nonbudding cells of B. dermatitidis may be confused
with Cryptococcus spp.
Cryptococcus spp. usually exhibits narrow-based
budding and has a capsule that is strongly positive
for mucicarmine, whereas B. dermatitidis usually
manifests broad-based budding and is negative or
weakly positive for mucicarmine stain
Capsule-deficient forms of Cryptococcus spp. can be
differentiated based on their positivity for FontanaMasson stain, as B. dermatitidis is negative for melanin
stains
Histoplasmosis
Very small yeast forms of B. dermatitidis (2-4 m) may
be confused with H. capsulatum
H. capsulatum may show narrow-based buds while B.
dermatitidis more often shows broad-based buds
Microforms of B. dermatitidis can be distinguished
by their positivity for Congo red stain, for which H.
capsulatum is negative
DIAGNOSTIC CHECKLIST
Clinically Relevant Pathologic Features
No clinical or radiographic abnormalities are
absolutely specific for blastomycosis
Spectrum of disease overlaps with those of other
fungal pathogens, mycobacteria, and malignancy
Visualization of characteristic yeast forms or growth of
fungus in culture is necessary to definitively diagnose
blastomycosis
Pathologic Interpretation Pearls
Round to oval multinucleated yeast (8-15 m in
diameter) cells with single broad-based budding and
thick refractile wall
Blastomycosis is often associated with formation
of microabscesses and pseudoepitheliomatous
hyperplasia in skin, and mucosal infection
Important to make use of special stains to look
for fungal organisms or concomitant infection by
mycobacteria if clinically indicated
5. Axelson GK et al: Evaluation of the use of Congo red
staining in the differential diagnosis of Candida vs.
various other yeast-form fungal organisms. J Cutan Pathol.
35(1):27-30, 2008
6. Chapman SW et al: Clinical practice guidelines for the
management of blastomycosis: 2008 update by the
Infectious Diseases Society of America. Clin Infect Dis.
46(12):1801-12, 2008
7. Johnson MD et al: Fungal infections of the bones and
joints. Curr Infect Dis Rep. 3(5):450-60, 2007
8. Pounder JI et al: Identification of Histoplasma capsulatum,
Blastomyces dermatitidis, and Coccidioides species
by repetitive-sequence-based PCR. J Clin Microbiol.
44(8):2977-82, 2006
9. Wheat LJ: Antigen detection, serology, and molecular
diagnosis of invasive mycoses in the immunocompromised
host. Transpl Infect Dis. 8(3):128-39, 2006
10. Durkin M et al: Antigen assay with the potential to aid in
diagnosis of blastomycosis. J Clin Microbiol. 42(10):4873-5,
2004
11. Bradsher RW et al: Blastomycosis. Infect Dis Clin North
Am. 17(1):21-40, vii, 2003
12. Martynowicz MA et al: Pulmonary blastomycosis: an
appraisal of diagnostic techniques. Chest. 121(3):768-73,
2002
13. Pappas PG: Blastomycosis in the immunocompromised
patient. Semin Respir Infect. 12(3):243-51, 1997
14. Stockman L et al: Evaluation of commercially available
acridinium ester-labeled chemiluminescent DNA probes
for culture identification of Blastomyces dermatitidis,
Coccidioides immitis, Cryptococcus neoformans, and
Histoplasma capsulatum. J Clin Microbiol. 31(4):845-50,
1993
15. Sheflin JR et al: Pulmonary blastomycosis: findings on
chest radiographs in 63 patients. AJR Am J Roentgenol.
154(6):1177-80, 1990
16. Drutz DJ et al: Intracellular and extracellular defenses
of human phagocytes against Blastomyces dermatitidis
conidia and yeasts. J Lab Clin Med. 105(6):737-50, 1985
17. Wages DS et al: Acid-fastness of fungi in blastomycosis and
histoplasmosis. Arch Pathol Lab Med. 106(9):440-1, 1982
SELECTED REFERENCES
1. Sidamonidze K et al: Real-time PCR assay for identification
of Blastomyces dermatitidis in culture and in tissue. J Clin
Microbiol. 50(5):1783-6, 2012
2. Guarner J et al: Histopathologic diagnosis of fungal
infections in the 21st century. Clin Microbiol Rev.
24(2):247-80, 2011
3. Bariola JR et al: Blastomycosis of the central nervous
system: a multicenter review of diagnosis and treatment in
the modern era. Clin Infect Dis. 50(6):797-804, 2010
4. Saccente M et al: Clinical and laboratory update on
blastomycosis. Clin Microbiol Rev. 23(2):367-81, 2010
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