Cutaneous infections Flashcards
What is the characteristic clinical feature of impetigo?
A) Hypopigmented macules with fine scaling
B) Honey-colored crusted papules, plaques, or bullae
C) Annular scaly plaques with central clearing
D) Inflammatory nodules with sinus tracts
Answer: B) Honey-colored crusted papules, plaques, or bullae
Rationale: Impetigo presents with honey-colored crusts, which are hallmark features of this bacterial skin infection caused by Group A Streptococcus and Staphylococcus aureus.
A patient presents with an annular scaly plaque with central clearing on the thigh. Which of the following is the most likely etiology?
A) Candida albicans
B) Malassezia furfur
C) Trichophyton spp.
D) Staphylococcus aureus
Answer: C) Trichophyton spp.
Rationale: Dermatophytosis (ringworm) is caused by Trichophyton, Epidermophyton, or Microsporum species and presents as annular, scaly plaques with central clearing.
Which of the following findings is characteristic of tinea versicolor on a KOH preparation?
A) Hyphae only
B) Pseudohyphae
C) “Spaghetti and meatballs” appearance
D) Gram-positive cocci in clusters
Answer: C) “Spaghetti and meatballs” appearance
Rationale: Tinea versicolor (caused by Malassezia furfur) exhibits both hyphae and spores, creating the classic “spaghetti and meatballs” pattern on KOH preparation.
What is the preferred treatment for dermatophytosis?
A) Topical selenium sulfide
B) Topical nystatin
C) Systemic or topical azoles, terbinafine, or griseofulvin
D) Oral acyclovir
Answer: C) Systemic or topical azoles, terbinafine, or griseofulvin
Rationale: Dermatophytosis is treated with topical azoles or systemic antifungals like terbinafine or griseofulvin (for extensive or scalp involvement). Nystatin is ineffective against dermatophytes.
A patient is diagnosed with impetigo. What is the recommended treatment?
A) Oral acyclovir
B) Topical selenium sulfide
C) Systemic or topical antistaphylococcal and antistreptococcal antibiotics
D) Oral griseofulvin
Answer: C) Systemic or topical antistaphylococcal and antistreptococcal antibiotics
Rationale: Impetigo is a bacterial infection caused by Staphylococcus aureus or Group A Streptococcus, treated with topical mupirocin or systemic antibiotics (e.g., cephalexin) in severe cases.
What is the first-line treatment for tinea versicolor?
A) Oral terbinafine
B) Topical selenium sulfide or azoles
C) Oral fluconazole
D) Topical mupirocin
Answer: B) Topical selenium sulfide or azoles
Rationale: Tinea versicolor (caused by Malassezia furfur) is treated with topical selenium sulfide, ketoconazole, or other azoles. Systemic therapy is reserved for extensive or recurrent cases.
Which dermatophyte infection is characterized by opacified, thickened nails and subungual debris?
A) Tinea capitis
B) Tinea corporis
C) Tinea unguium
D) Tinea cruris
Answer: C) Tinea unguium
Rationale: Tinea unguium (onychomycosis) affects the nails, causing thickening, discoloration, and subungual debris accumulation.
Which of the following fungal species is most commonly responsible for tinea capitis?
A) Malassezia furfur
B) Candida albicans
C) Trichophyton tonsurans
D) Epidermophyton floccosum
Answer: C) Trichophyton tonsurans
Rationale: Tinea capitis (scalp ringworm) is most commonly caused by Trichophyton tonsurans in the U.S., leading to hair loss and scaling.
What is the best diagnostic method for confirming dermatophytosis?
A) Wood’s lamp examination
B) Direct microscopic examination with KOH
C) Gram stain
D) Skin biopsy with hematoxylin and eosin (H&E) stain
Answer: B) Direct microscopic examination with KOH
Rationale: KOH preparation is the preferred initial diagnostic test, allowing visualization of fungal hyphae in skin, hair, or nail scrapings.
Which oral antifungal agent is FDA-approved for the treatment of onychomycosis?
A) Griseofulvin
B) Fluconazole
C) Itraconazole
D) Nystatin
Answer: C) Itraconazole
Rationale: Itraconazole and terbinafine are approved for the treatment of onychomycosis. Griseofulvin is effective but not specifically FDA-approved for this indication.
What is the causative organism of tinea (pityriasis) versicolor?
A) Trichophyton rubrum
B) Epidermophyton floccosum
C) Malassezia furfur
D) Candida albicans
Answer: C) Malassezia furfur
Rationale: Tinea versicolor is caused by Malassezia furfur, a dimorphic fungus that is a normal skin inhabitant but can overgrow in warm and humid conditions.
Which of the following is a characteristic feature of tinea versicolor on a KOH preparation?
A) Hyphae with chlamydospores
B) Septate branching hyphae
C) Pseudohyphae with budding yeast
D) Short hyphae and round spores (“spaghetti and meatballs”)
Answer: D) Short hyphae and round spores (“spaghetti and meatballs”)
Rationale: Tinea versicolor exhibits a characteristic “spaghetti and meatballs” appearance under KOH microscopy, showing clusters of short hyphae and spores.
What is the first-line topical treatment for tinea versicolor?
A) Topical nystatin
B) Selenium sulfide lotion
C) Topical terbinafine
D) Oral ketoconazole
Answer: B) Selenium sulfide lotion
Rationale: Selenium sulfide lotion, along with sulfur and salicylic acid preparations, is the preferred topical treatment for tinea versicolor. It should be used daily for 1–2 weeks and then weekly to prevent recurrence.
What is the most appropriate treatment for oral candidiasis (thrush)?
A) Oral terbinafine
B) Topical nystatin or oral fluconazole
C) Selenium sulfide lotion
D) Griseofulvin
Answer: B) Topical nystatin or oral fluconazole
Rationale: Nystatin is effective for localized oral candidiasis, while fluconazole is used for more extensive or recurrent cases.
In which of the following conditions should oral ketoconazole be avoided?
A) Tinea versicolor
B) Onychomycosis
C) Patients with liver disease
D) Patients with mild tinea pedis
Answer: C) Patients with liver disease
Rationale: Oral ketoconazole has hepatotoxicity concerns and is generally avoided due to the risk of liver damage.
Which HPV types are most strongly associated with cervical and anogenital cancers?
A) HPV 6 and 11
B) HPV 16 and 18
C) HPV 1 and 4
D) HPV 33 and 45
Answer: B) HPV 16 and 18
Rationale: HPV types 16 and 18 are high-risk oncogenic strains linked to cervical, vulvar, anal, and penile squamous cell carcinomas.
Which of the following is a first-line treatment for common warts?
A) Podophyllin
B) Cryotherapy with liquid nitrogen
C) Topical imiquimod
D) Oral acyclovir
Answer: B) Cryotherapy with liquid nitrogen
Rationale: Cryotherapy is a widely used, effective treatment for common warts. It is a quick procedure with minimal side effects and good patient compliance.
Which treatment is FDA-approved for genital warts and works by inducing local cytokine release?
A) Salicylic acid
B) Topical imiquimod
C) Cryotherapy
D) Laser therapy
Answer: B) Topical imiquimod
Rationale: Imiquimod is an immune response modifier that induces cytokine release, helping clear HPV-infected cells in genital warts.
What is the causative bacterial organism implicated in acne vulgaris?
A) Staphylococcus aureus
B) Streptococcus pyogenes
C) Cutibacterium acnes
D) Pseudomonas aeruginosa
Answer: C) Cutibacterium acnes
Rationale: Cutibacterium acnes (formerly Propionibacterium acnes) contributes to inflammation by releasing free fatty acids from sebum, leading to follicular rupture and immune response.
What is the distinguishing feature of a closed comedone (whitehead)?
A) A dilated follicular orifice filled with dark debris
B) An inflamed, pus-filled lesion
C) A 1–2 mm papule with a blocked follicular orifice
D) A painful nodule with scarring potential
Answer: C) A 1–2 mm papule with a blocked follicular orifice
Rationale: Closed comedones (whiteheads) are small, white papules formed by keratin and sebum retention within a blocked follicular orifice. Unlike open comedones (blackheads), they are not oxidized.
Which of the following medications can aggravate acne?
A) Benzoyl peroxide
B) Retinoic acid
C) Lithium
D) Salicylic acid
Answer: C) Lithium
Rationale: Systemic medications like lithium, corticosteroids, androgenic steroids, and certain anticonvulsants (e.g., phenytoin, phenobarbital) can exacerbate or induce acneiform eruptions.
Which combination of topical therapy is recommended to prevent bacterial resistance in acne treatment?
A) Retinoic acid and salicylic acid
B) Benzoyl peroxide and topical antibiotics
C) Salicylic acid and azelaic acid
D) Clindamycin and erythromycin
Answer: B) Benzoyl peroxide and topical antibiotics
Rationale: Benzoyl peroxide reduces bacterial resistance when combined with topical antibiotics (erythromycin or clindamycin), improving treatment efficacy and preventing antimicrobial resistance.
In female patients with acne who do not respond to oral antibiotics, which treatment is often considered?
A) Isotretinoin
B) Spironolactone
C) Minocycline
D) Salicylic acid
Answer: B) Spironolactone
Rationale: Spironolactone is an antiandrogen that reduces sebum production and is effective in female patients who fail to respond to oral antibiotics. Several oral contraceptives are also FDA-approved for acne treatment.
What is the most significant adverse effect of isotretinoin therapy?
A) Hyperpigmentation
B) Teratogenicity
C) Hypoglycemia
D) Liver cirrhosis
Answer: B) Teratogenicity
Rationale: Isotretinoin is highly teratogenic and requires strict pregnancy prevention measures, including two negative pregnancy tests before initiation and monthly pregnancy tests during therapy. Other side effects include dry skin, cheilitis, and hypertriglyceridemia.
