Dimorphic fungi

Dimorphic fungi US Medical PG Question 1: A 34-year-old woman presents with multiple round, scaly patches on her chest and back. The lesions are hypopigmented and slightly pruritic. KOH preparation of skin scrapings shows short, angular hyphae. Which of the following best describes the causative organism's morphology in culture?

• A. Branching, septate hyphae with characteristic 'spaghetti and meatballs' appearance (Correct Answer)
• B. Non-septate hyphae with sporangiospores
• C. Branching, septate hyphae with tear-drop microconidia
• D. Pseudohyphae with blastoconidia

Dimorphic fungi Explanation: ***Branching, septate hyphae with characteristic 'spaghetti and meatballs' appearance*** - The clinical presentation of **hypopigmented, scaly patches** on the trunk, especially with mild pruritus, is highly suggestive of **tinea versicolor**. - A **KOH preparation** showing **short, angular hyphae** is characteristic of *Malassezia furfur*, which when cultured, displays both **mycelial elements (spaghetti)** and **yeast forms (meatballs)**. *Non-septate hyphae with sporangiospores* - This morphology is characteristic of **zygomycetes** (e.g., *Rhizopus*, *Mucor*), which cause diseases like mucormycosis, a much more severe and rapidly progressive infection, not tinea versicolor. - **Zygomycetes** are typically associated with invasive infections in immunocompromised individuals. *Branching, septate hyphae with tear-drop microconidia* - This describes the typical dermatophyte, *Trichophyton rubrum*, which causes conditions like tinea pedis, tinea cruris, and tinea corporis, usually presenting with **erythematous, annular lesions** with active borders, different from tinea versicolor. - While it also has septate hyphae, the distinct microconidia morphology differentiates it from *Malassezia*. *Pseudohyphae with blastoconidia* - This morphology is typical of **Candida species**, which cause conditions like candidiasis (e.g., thrush, diaper rash, vulvovaginitis). - Though *Candida* can cause skin infections, the hypopigmentation and characteristic KOH findings of short, angular hyphae are inconsistent with *Malassezia*.

Dimorphic fungi US Medical PG Question 2: A young woman from the Ohio River Valley in the United States currently on corticosteroid therapy for ulcerative colitis presented to a clinic complaining of fever, sweat, headache, nonproductive cough, malaise, and general weakness. A chest radiograph revealed patchy pneumonia in the lower lung fields, together with enlarged mediastinal and hilar lymph nodes. Skin changes suggestive of erythema nodosum (i.e. an acute erythematous eruption) were noted. Because the patient was from a region endemic for fungal infections associated with her symptoms and the patient was in close contact with a person presenting similar symptoms, the attending physician suspected that systemic fungal infection might be responsible for this woman’s illness. Which of the following laboratory tests can the physician use to ensure early detection of the disease, and also effectively monitor the treatment response?

• A. Skin tests
• B. Fungal staining
• C. Antigen detection (Correct Answer)
• D. Culture method
• E. Antibody testing

Dimorphic fungi Explanation: ***Antigen detection*** - **Antigen detection assays** (e.g., *Histoplasma galactomannan antigen*) are highly sensitive for **disseminated histoplasmosis**, especially in immunosuppressed patients like this one on corticosteroids. - They provide **early diagnosis** and are effective for **monitoring treatment response**, as antigen levels typically decrease with successful therapy. *Skin tests* - **Skin tests** (e.g., *histoplasmin skin test*) indicate **prior exposure** to the fungus and are not useful for diagnosing active, acute infection. - A positive skin test does not differentiate between past exposure and current disease, making it unsuitable for early detection or monitoring. *Fungal staining* - **Fungal staining** of patient samples (e.g., sputum, biopsy) can reveal fungal elements but has **limited sensitivity** and may not identify the specific pathogen. - It often requires **invasive procedures** to obtain suitable specimens and is not ideal for routine monitoring of treatment response due to variability. *Culture method* - **Fungal cultures** are a **definitive diagnostic method** but can take **several weeks** to yield results, which is too slow for early detection in an acutely ill patient. - While useful for species identification and susceptibility testing, the **delayed turnaround time** makes it impractical for monitoring rapid treatment changes. *Antibody testing* - **Antibody tests** for fungal infections can be useful but may show **false negatives in immunocompromised patients** (like this patient on corticosteroids) due to a blunted immune response. - Seroconversion or a significant rise in antibody titers can indicate infection, but antibodies may **persist long after resolution**, making them less reliable for monitoring acute treatment efficacy.

Dimorphic fungi US Medical PG Question 3: An investigator is studying growth patterns of various fungal pathogens. Incubation of an isolated fungus at 25°C shows branching hyphae with rosettes of conidia under light microscopy. After incubation at 37°C, microscopic examination of the same organism instead shows smooth, white colonies with rounded, elongated cells. Infection with the investigated pathogen is most likely to cause which of the following conditions?

• A. Pityriasis versicolor
• B. Candidiasis
• C. Cryptococcosis
• D. Sporotrichosis (Correct Answer)
• E. Coccidioidomycosis

Dimorphic fungi Explanation: ***Sporotrichosis*** - The description of a fungal pathogen exhibiting **thermal dimorphism** (different forms at 25°C and 37°C) is characteristic of **Sporothrix schenckii**. - At 25°C, it typically grows as **mold with branching hyphae and conidia in rosettes**, and at 37°C, it grows as **yeast-like cells (cigar-shaped bodies in tissue)**, which can appear rounded and elongated. *Pityriasis versicolor* - Caused by **Malassezia globosa**, which is a **lipophilic yeast** and does not exhibit thermal dimorphism described here. - Characterized by **hypo- or hyperpigmented skin patches**, not deep tissue infection with dimorphic growth. *Candidiasis* - Caused by **Candida species**, which are **opportunistic yeasts** that can form pseudohyphae and true hyphae but do not display the specific dimorphism with rosettes of conidia at 25°C. - Infections range from superficial mucocutaneous to systemic, but the fungal morphology described does not fit. *Cryptococcosis* - Caused by **Cryptococcus neoformans** or **Cryptococcus gattii**, which are **encapsulated yeasts** and do not exhibit dimorphism (mold at 25°C, yeast at 37°C). - Primarily causes **meningoencephalitis** or pulmonary disease, and is identified by its capsule and yeast form. *Coccidioidomycosis* - Caused by **Coccidioides immitis** or **Coccidioides posadasii**, which are **thermally dimorphic fungi**, but their morphology differs from the description. - At 25°C, they grow as molds with **arthroconidia**, and at 37°C, they form **spherules containing endospores** in tissue, not smooth, white colonies with rounded, elongated cells.

Dimorphic fungi US Medical PG Question 4: A 73-year-old man presents to the office, complaining of “weird blisters” on his right hand, which appeared 2 weeks ago. The patient says that he initially had a rash, which progressed to blisters. He denies any trauma or known contact with sick people. He is worried because he hasn’t been able to garden since the rash appeared, and he was planning on entering his roses into an annual competition this month. His vital signs are stable. On physical exam, the patient has multiple bullae accompanied by red, papular lesions on his right hand, which progress to his forearm. The right axillary lymph nodes are swollen and tender. What is the treatment for the most likely diagnosis of this patient?

• A. Itraconazole (Correct Answer)
• B. Azithromycin
• C. Topical corticosteroids
• D. Doxycycline
• E. Potassium iodide solution

Dimorphic fungi Explanation: ***Itraconazole*** - This patient likely has **sporotrichosis**, a subcutaneous fungal infection, given the history of **gardening** (exposure to soil/plants), **papular lesions progressing to blisters**, and **lymphatic spread** (swollen axillary lymph nodes). - **Itraconazole** is the **first-line treatment** for cutaneous and lymphocutaneous sporotrichosis. *Azithromycin* - **Azithromycin** is an **antibiotic** used to treat bacterial infections, not fungal infections like sporotrichosis. - It is often used for respiratory tract infections, sexually transmitted infections, and some skin infections. *Topical corticosteroids* - **Topical corticosteroids** are anti-inflammatory agents that would likely worsen a fungal infection by suppressing the immune response. - They are used for inflammatory dermatoses like eczema or psoriasis and would not be effective against sporotrichosis. *Doxycycline* - **Doxycycline** is a broad-spectrum **antibiotic**, effective against a variety of bacterial infections, including some atypical pathogens. - It has no antifungal activity and would not be an appropriate treatment for sporotrichosis. *Potassium iodide solution* - While traditionally used for sporotrichosis, **potassium iodide (KI) solution** is now considered a **second-line treatment** due to its side effects and the availability of more effective and safer antifungals like itraconazole. - It is used only in cases where itraconazole is contraindicated or ineffective.

Dimorphic fungi US Medical PG Question 5: A 19-year-old woman comes to the physician because of worsening pain with swallowing for 3 days and a dry sensation in the mouth over the past week. She has a history of asthma controlled with inhaled fluticasone and albuterol. Physical examination shows white plaques on the dorsal surface of the tongue and buccal mucosa that bleed when scraped off. Which of the following is the most appropriate pharmacotherapy?

• A. Amphotericin B
• B. Nystatin (Correct Answer)
• C. Acyclovir
• D. Griseofulvin
• E. Triamcinolone

Dimorphic fungi Explanation: **Nystatin** - The patient's presentation with **white plaques on the dorsal surface of the tongue and buccal mucosa that bleed when scraped off**, along with a history of inhaled fluticasone use, is highly suggestive of **oral candidiasis (thrush)**. - **Nystatin** is an antifungal medication typically used as a **topical swish and swallow solution** for oral candidiasis, effectively treating localized infections with minimal systemic absorption. *Amphotericin B* - **Amphotericin B** is a potent systemic antifungal used for **severe, invasive fungal infections**, often given intravenously due to significant side effects. - It is **not the first-line treatment** for localized oral candidiasis, which is typically managed with less toxic topical agents. *Acyclovir* - **Acyclovir** is an **antiviral medication** used to treat **herpes simplex virus (HSV)** infections, such as oral herpes or cold sores. - The patient's symptoms are characteristic of a fungal infection, not a viral one. *Griseofulvin* - **Griseofulvin** is an **oral antifungal primarily used for dermatophyte infections** of the skin, hair, and nails (e.g., tinea capitis, onychomycosis). - It is ineffective against *Candida* species and therefore not appropriate for oral candidiasis. *Triamcinolone* - **Triamcinolone** is a **corticosteroid** used to reduce inflammation and is often found in topical creams or inhaled formulations. - Corticosteroids can actually **worsen fungal infections** like candidiasis by suppressing the immune response, and are therefore contraindicated.

Dimorphic fungi US Medical PG Question 6: A 40-year-old farmer from Ohio seeks evaluation at a clinic with complaints of a chronic cough, fevers, and anorexia of several months duration. On examination, he has generalized lymphadenopathy with hepatosplenomegaly. A chest radiograph reveals local infiltrates and patchy opacities involving all lung fields. Fine needle aspiration of an enlarged lymph node shows the presence of intracellular yeast. A fungal culture shows the presence of smooth, thin-walled microconidia and tuberculate macroconidia. Which of the following is the most likely diagnosis?

• A. Coccidioidomycosis
• B. Blastomycosis
• C. Cryptococcosis
• D. Histoplasmosis (Correct Answer)
• E. Sporotrichosis

Dimorphic fungi Explanation: ***Histoplasmosis*** - **Histoplasmosis** is characterized by the presence of **intracellular yeast** in tissue samples and **tuberculate macroconidia** in fungal cultures, which are key diagnostic findings in this case. - The patient's presentation with chronic cough, fevers, anorexia, generalized lymphadenopathy, hepatosplenomegaly, and lung infiltrates, along with geographic exposure in **Ohio** (part of the Ohio River Valley endemic area), is highly consistent with disseminated histoplasmosis. *Coccidioidomycosis* - While coccidioidomycosis can cause lung infiltrates, it is typically endemic to the **southwestern United States** and Mexico, not Ohio. - Microscopic examination would reveal **spherules** containing endospores, not intracellular yeast with tuberculate macroconidia. *Blastomycosis* - Blastomycosis is also endemic to the Ohio River Valley, but it is characterized by **broad-based budding yeast** in tissue, and its cultures typically do not show tuberculate macroconidia. - While it causes pulmonary and disseminated disease, the specific microscopic and culture findings differentiate it from histoplasmosis. *Cryptococcosis* - Cryptococcosis primarily affects immunocompromised individuals and is characterized by encapsulated yeast, which would be visible with India ink stain. - It typically presents as **meningitis** or pneumonia, and its culture morphology does not include tuberculate macroconidia. *Sporotrichosis* - Sporotrichosis is commonly associated with **cutaneous lesions** following traumatic inoculation of spores from soil or vegetation, and it rarely causes disseminated disease with extensive systemic symptoms like those described. - The yeast forms in tissue are typically smaller and cigar-shaped, and the culture morphology differs significantly from what is described.

Dimorphic fungi US Medical PG Question 7: A 44-year-old man comes to the physician because of a 3-week history of productive cough, fever, and lethargy. He also has several skin lesions over his body. His symptoms began 3 weeks after he returned from a camping trip in Kentucky. Three years ago, he underwent kidney transplantation for polycystic kidney disease. Current medications include sirolimus and prednisone. His temperature is 38°C (100.4°F). Diffuse crackles are heard over the lung fields. There are 4 white, verrucous skin patches over his chest and upper limbs. A photomicrograph of a skin biopsy specimen from one of the lesions is shown. Which of the following is the most likely diagnosis?

• A. Coccidioidomycosis
• B. Mucormycosis
• C. Blastomycosis (Correct Answer)
• D. Cryptococcosis
• E. Histoplasmosis

Dimorphic fungi Explanation: ***Blastomycosis*** - The patient's history of **camping in Kentucky**, along with the presence of **pulmonary symptoms** (productive cough, fever, crackles) and **verrucous skin lesions**, are classic for blastomycosis. - The photomicrograph showing **broad-based budding yeast** is pathognomonic for *Blastomyces dermatitidis*. *Coccidioidomycosis* - This is typical in the **Southwestern United States and parts of Mexico**, not Kentucky. - Microscopic examination would reveal **spherules containing endospores**, which are not seen in the provided image. *Mucormycosis* - This infection is characterized by **irregular, broad, non-septate hyphae** with **wide-angle branching**, often invading blood vessels, leading to tissue necrosis. - It primarily affects immunocompromised patients but typically presents as **rhinocerebral** or **pulmonary infection**, less commonly with verrucous skin lesions of this type. *Cryptococcosis* - Primarily affects the **lungs and central nervous system**, especially in immunocompromised individuals. - Microscopy typically shows **encapsulated yeast** cells, which would be visible with India ink stain, and are not represented by the broad-based budding in the image. *Histoplasmosis* - Prevalent in the **Ohio and Mississippi River Valleys**, which includes Kentucky, and is often associated with **bird or bat droppings**. - On microscopy, it presents as **small intracellular yeast** within macrophages, which is morphologically distinct from the large, broad-based budding yeast shown.

Dimorphic fungi US Medical PG Question 8: A 16-year-old boy presents to his pediatrician because he has noticed white plaques forming on his tongue over the last 5 days. He recently returned from a boy scout trip where he traveled across the country and hiked through the woods. His past medical history is significant for asthma for which he uses an inhaler as needed. He says that during the trip he felt short of breath several times and had to use the inhaler. He also says that several of his friends appeared to get sick on the same trip and were coughing a lot. He has not experienced any other symptoms since returning from the trip. On presentation, he is found to have white plaques on the tongue that can be scraped off. Which of the following is a characteristic of the most likely cause of this patient's disease?

• A. Acute angle branching
• B. Spherules containing endospores
• C. Germ tube formation (Correct Answer)
• D. Latex agglutination
• E. Broad-based budding

Dimorphic fungi Explanation: ***Germ tube formation*** - This patient presents with **oral thrush (candidiasis)**, characterized by **white plaques on the tongue that can be scraped off**. His history of **asthma and inhaler use** (likely corticosteroids) is a risk factor. - **Germ tube formation** is a rapid diagnostic test for *Candida albicans*, the most common cause of oral thrush, where yeast cells produce filament-like extensions when incubated in serum. *Acute angle branching* - This is characteristic of **Aspergillus species**, which typically cause invasive mold infections in immunocompromised individuals, or allergic bronchopulmonary aspergillosis, not oral thrush. - *Aspergillus* infections are not typically associated with easily scraped-off oral plaques. *Spherules containing endospores* - **Spherules containing endospores** are the characteristic tissue form of **Coccidioides immitis/posadasii**, a dimorphic fungus causing coccidioidomycosis (Valley fever), typically presenting as a pulmonary infection. - This feature is not associated with *Candida albicans* or oral thrush, though the patient's travel history could suggest dimorphic fungal exposure. *Latex agglutination* - **Latex agglutination** is a serological test primarily used for detecting **cryptococcal capsular antigen** in cerebrospinal fluid or serum, indicating cryptococcosis. - It is not a characteristic feature or primary diagnostic method for *Candida* infections like oral thrush. *Broad-based budding* - **Broad-based budding** is a microscopic characteristic of **Blastomyces dermatitidis**, a dimorphic fungus causing blastomycosis, typically a pulmonary infection that can disseminate to skin, bone, or other organs. - This feature is not associated with *Candida albicans* or oral thrush.

Dimorphic fungi US Medical PG Question 9: A 50-year-old HIV-positive male presents to the ER with a two-day history of fever and hemoptysis. Chest radiograph shows a fibrocavitary lesion in the right middle lobe. Biopsy of the afflicted area demonstrates septate hyphae that branch at acute angles. Which of the following is the most likely causal organism?

• A. Mycobacterium tuberculosis
• B. Pneumocystis jirovecii
• C. Aspergillus fumigatus (Correct Answer)
• D. Candida albicans
• E. Mucor species

Dimorphic fungi Explanation: ***Aspergillus fumigatus*** - The combination of **fever**, **hemoptysis**, a **fibrocavitary lesion** in an **HIV-positive** patient, and the presence of **septate hyphae branching at acute angles** on biopsy are classic findings for invasive **aspergillosis**. - **Aspergillus** specifically targets individuals with compromised immune systems, and the pathological description of the hyphae is highly characteristic of this fungus. *Mycobacterium tuberculosis* - While **Mycobacterium tuberculosis** can cause **fever**, **hemoptysis**, and **cavitary lesions** in HIV-positive patients, the microscopic description of **septate hyphae branching at acute angles** is not consistent with bacterial infection. - Tuberculosis is characterized by **acid-fast bacilli** and granulomatous inflammation, not fungal hyphae. *Mucor species* - **Mucor** (along with Rhizopus) causes **mucormycosis**, an invasive fungal infection that can affect immunocompromised patients and present with pulmonary involvement and cavitary lesions. - However, mucormycosis is characterized by **non-septate (aseptate) hyphae branching at right (90-degree) angles**, not septate hyphae at acute angles, making it distinguishable from Aspergillus. *Pneumocystis jirovecii* - **Pneumocystis jirovecii** is a common cause of pneumonia in HIV-positive patients, typically presenting as **diffuse interstitial infiltrates** rather than cavitary lesions. - Microscopic examination would reveal **cysts** and **trophozoites**, not septate hyphae, making it inconsistent with the biopsy findings. *Candida albicans* - While **Candida albicans** can cause infections in immunocompromised individuals, it typically presents as **oral thrush**, esophagitis, or disseminated candidiasis. - Pulmonary involvement is less common and usually manifests as **pneumonitis** rather than cavitary lesions, and its hyphae are typically **pseudohyphae** or budding yeasts, not septate hyphae branching at acute angles.

Dimorphic fungi US Medical PG Question 10: A 28-year-old woman with a past history of type 1 diabetes presents to your office with a 2-week history of vaginal itching and soreness accompanied by a white, clumpy vaginal discharge which she says resembles cheese curds. Her last HbA1c from a month ago was 7.8%, and her last cervical cytology from 10 months ago was reported as normal. She has a blood pressure of 118/76 mmHg, respiratory rate of 14/min, and heart rate of 74/min. Pelvic examination reveals multiple small erythematous lesions in the inguinal and perineal area, vulvar erythema, and excoriations. Inspection demonstrates a normal cervix and a white, adherent, thick, non-malodorous vaginal discharge. Which of the following is most likely to be present in a saline wet mount from the vaginal discharge of this patient?

• A. Clue cells on saline smear
• B. Gram-negative diplococci
• C. Hyphae (Correct Answer)
• D. Motile flagellates
• E. Multinucleated giant cells

Dimorphic fungi Explanation: ***Hyphae*** - The patient's symptoms of **vaginal itching**, soreness, and a **white, clumpy discharge resembling cheese curds** are classic for **vulvovaginal candidiasis** (yeast infection). - A **saline wet mount** in such cases typically reveals **hyphae** and **budding yeast forms** of *Candida albicans*. *Clue cells on saline smear* - **Clue cells** are characteristic of **bacterial vaginosis**, which is typically associated with a **thin, grayish discharge** and a **fishy odor** (amine odor), neither of which are described here. - The discharge in this patient is described as **thick and non-malodorous**, which is inconsistent with bacterial vaginosis. *Gram-negative diplococci* - **Gram-negative diplococci** are the hallmark of **gonorrhea**, caused by *Neisseria gonorrhoeae*. - Gonorrhea often presents with **purulent discharge** and cervical inflammation, or it can be asymptomatic; it does not typically cause the **clumpy discharge** and intense itching seen in this patient. *Motile flagellates* - **Motile flagellates** are characteristic of **trichomoniasis**, caused by *Trichomonas vaginalis*. - This infection usually presents with a **frothy, yellow-green discharge**, a **fishy odor**, and cervical petechiae (strawberry cervix), which are not a feature of this patient's presentation. *Multinucleated giant cells* - **Multinucleated giant cells** are indicative of **herpes simplex virus (HSV) infection**, particularly when found on a **Tzanck smear** of a lesion. - While the patient has erythematous lesions, the primary complaint of **vaginal discharge** and itching points away from herpes as the main cause of the discharge.

Dimorphic fungi Flashcard 1 of 10

Question: Paracoccidioidomycosis is a _____ fungus that changes form with different temperatures

Answer: dimorphic

Dimorphic fungi Flashcard 2 of 10

Question: Candida albicans is _____, meaning it assumes different forms depending on the temperature of its environment

Answer: dimorphic**

Dimorphic fungi Flashcard 3 of 10

Question: Besides histoplasmosis, which other fungus can be detected through urine antigen testing?_____

Answer: Blastomycosis

Dimorphic fungi Flashcard 4 of 10

Question: Sporothrix schenckii

Answer: dipmorphic, cigar-shaped, budding yeast

Extra Information: "rose gardener's disease"itraconazole or potassium iodide

Dimorphic fungi Flashcard 5 of 10

Question: Dimorphic fungi exhibit a _____ morphology at ambient temperature and _____ morphology at body temperature.

Answer: mold

Dimorphic fungi Flashcard 6 of 10

Question: Histoplasma spp.

Answer: dimorphic

Extra Information: histoplasmosislocal - fluconazole or itraconazole systemic - amphotericin B bird or bat droppingsOhio River valley

Dimorphic fungi Flashcard 7 of 10

Question: Blastomycces spp.

Answer: dimorphic, broad-base budding

Extra Information: pneumonialocal - fluconazole or itraconazole systemic - amphotericin B East of Mississippi and Central America

Dimorphic fungi Flashcard 8 of 10

Question: Coccidiomycces spp.

Answer: dimorphic

Extra Information: pneumonia, meningitislocal - fluconazole or itraconazole systemic - amphotericin B Southwestern US, California, San Joaquin valley

Dimorphic fungi Flashcard 9 of 10

Question: Paracoccidiomycces spp.

Answer: dimorphic, "Captain's Wheel"

Extra Information: pneumonialocal - fluconazole or itraconazole systemic - amphotericin B Latin America

Dimorphic fungi Flashcard 10 of 10

Question: Candida albicans

Answer: dimorphic

Extra Information: systemic or superficial infection (thrush, vulvovaginitis, daiper rash, endocarditis...)local - topical azole systemic - fluconazole, amphotericin B, capsofungin