Infections & Infestations (incl. regional)

A 6-year-old boy has honey-colored crusts around the nostrils without fever. First-line treatment?

A 3-year-old develops flaccid bullae on trunk; cultures grow S. aureus producing exfoliative toxin. Best therapy?

A 35-year-old fisherman has sharply demarcated, fiery-red facial plaque with fever following minor cheek abrasion. Diagnosis and step?

A 52-year-old with recurrent cellulitis of the leg also has interdigital scaling and maceration between toes. Key preventive measure?

After hot-tub exposure, a 20-year-old develops widespread pruritic papulopustules in swimsuit distribution. Best management?

A landscaper develops a painless, ulcerated nodule on forearm with lymphangitic spread of subcutaneous nodules. Most likely and treatment?

A 28-year-old with intensely pruritic serpiginous track on plantar foot after beach trip. Best therapy?

A 4-year-old with scalp scaling, alopecia patches, and posterior cervical nodes. Best treatment?

A 33-year-old has annular scaly plaque with active border and central clearing on thigh; KOH positive for hyphae. First-line?

A 40-year-old with folliculocentric pustules on back and chest fails repeated oral antibiotics; KOH shows budding yeast. Diagnosis/therapy?

A 25-year-old with crusted, hyperkeratotic widespread scabies and nail involvement; lives in nursing facility. Best regimen?

A mother asks how to manage contacts for classic scabies in her child. Correct advice?

A 30-year-old woman in first trimester has generalized pruritus with nocturnal exacerbation, burrows on wrists/finger webs. Best treatment?

After successful scabies treatment, pruritus persists for 3 weeks without new burrows. Explanation?

A 7-year-old with pediculosis capitis; family asks best first-line.

A 24-year-old with multiple dome-shaped, umbilicated papules on thighs/genitals; mild eczema around lesions. Best management?

A 36-year-old diabetic with rapidly progressive painful erythematous skin, violaceous bullae, crepitus, and systemic toxicity. Next best step?

A neutropenic patient develops painless black necrotic ulcers with surrounding erythema on the trunk; blood cultures pending. Likely pathogen and step?

A 29-year-old woman with recurrent painful nodular lesions in hair-bearing labia majora diagnosed as furunculosis; culture MRSA. Best outpatient therapy?

A 55-year-old with sharply demarcated brown-red patches in groin; Wood lamp shows coral-red fluorescence. Best treatment?

A 34-year-old with a chronic crusted painless papule on forearm acquired after travel to the Middle East; smear shows intracellular amastigotes. Best therapy?

A 26-year-old pregnant woman with suspected cutaneous leishmaniasis (PCR positive). Preferred management?

A 49-year-old man with anesthetic hypopigmented patch on elbow, thickened ulnar nerve, and reduced pinprick sensation. Most likely diagnosis?

A patient with leprosy develops tender subcutaneous nodules, fever, and malaise during treatment (ENL). Best acute management?

A hyperpigmented, scaly macular eruption on trunk; KOH shows “spaghetti and meatballs.” First-line?

A 60-year-old with painful vesicles in trigeminal V1 distribution and eye redness. Immediate management?

A 22-year-old with recurrent “cold sores” worsened by sun exposure. Best suppressive strategy?

A 45-year-old with onychomycosis of toenails confirmed by KOH. Best systemic therapy and key monitoring?

A 19-year-old with painful vesiculopustular eruption limited to eczematous areas; fever and malaise. Next step?

A 38-year-old with perianal itchy plaques and satellite pustules; KOH positive for pseudohyphae. Best therapy?

A traveler develops painless black eschar with surrounding edema on forearm after handling animal hides. Likely diagnosis?

A 27-year-old man with tinea cruris fails OTC steroids/antifungal combo; lesion worsened with steroid. Best current management?

A 55-year-old gardener with verrucous plaque on leg; biopsy shows pigmented “copper penny” sclerotic bodies. Diagnosis/therapy?

A 30-year-old farmer with chronic draining sinuses and “grains” from plantar foot swelling. Likely condition and first-line?

A sexually active 24-year-old pregnant woman has exophytic anogenital warts. Best management?

A 42-year-old with acute paronychia after nail-biting presents with throbbing pain and erythema. Best next step?

A 60-year-old with green nail discoloration after chronic water exposure and onycholysis. Diagnosis and therapy?

A 22-year-old with tinea barbae from a pet kitten shows inflammatory plaques with pustules on beard area. Best treatment?

A 34-year-old develops nodular lymphangitis after sandfly bites; lesion aspirate shows amastigotes. Best systemic option for complicated disease?

A 48-year-old with painful, foul-smelling plantar pits and hyperhidrosis from occlusive shoes. Most likely and treatment?

A 38-year-old aquarium hobbyist develops violaceous papulonodules along a scratch on the hand with sporotrichoid spread; culture grows photochromogenic mycobacteria. Best treatment?

A 29-year-old wrestler has annular scaly plaques on face and neck; teammates affected. Best initial management?

A 48-year-old fisherman presents with a violaceous, painful plaque on the finger after handling raw fish; no systemic symptoms. Likely pathogen and therapy?

A 7-year-old boy with tender honey-crusted ulcers penetrating into the dermis on shins; regional nodes palpable. Therapy?

A pregnant 26-year-old with erythema migrans after tick bite. Best treatment?

A 55-year-old with a persistent subcutaneous painless nodule on forearm with a central punctum and movement sensation; recently returned from the tropics. Diagnosis/management?

A 9-year-old with intensely pruritic papules in linear clusters on exposed arms after travel; morning examination shows small blood spots on sheets. Likely cause and step?

A 30-year-old with acne on long-term oral antibiotics develops pustular folliculitis by Gram-negative rods. Best next step?

A 40-year-old butcher develops a single umbilicated violaceous nodule on the hand after lambing season; no systemic signs. Most likely?

A 32-year-old with tinea pedis (moccasin type) and unilateral scaly palm (“two feet–one hand” syndrome). Best therapy?

A 65-year-old with recurrent cellulitis of the leg and chronic edema. Preventive strategy besides tinea care?

A 23-year-old diver develops verrucous plaques on the dorsum of the hand after coral injury; KOH negative; culture grows dematiaceous fungi. Diagnosis/therapy?

A 42-year-old with chronic wet work has painful swollen proximal nail folds with transverse nail ridging. Likely and management?

A 36-year-old develops subcutaneous nodules and lymphangitis after thorn injury; smear shows branching filamentous, weakly acid-fast organisms. Best therapy?

A 28-year-old returns from West Africa with a painful papule on the toe with a central black dot; radiograph shows a small intradermal cavity. Diagnosis/management?

A 52-year-old diabetic with interdigital maceration develops malodorous ulcers with green hue and undermined borders on the foot. Best empiric coverage?

A 6-year-old child has high fever then sudden defervescence with rose-pink macules on trunk/neck. Diagnosis?

A 22-year-old college student with fever, malaise, and painful oral ulcers plus targetoid macules on hands/feet after HSV outbreak. Diagnosis/management?

A 35-year-old HIV+ (CD4 90) with multiple molluscum contagiosum on face/eyelids. Best approach?

A 44-year-old gardener has painful nodules and draining sinuses on leg; grains are white-to-yellow and culture grows Nocardia brasiliensis. Diagnosis/therapy?

A 58-year-old with burning grouped vesicles on erythematous base on the chest; Tzanck smear shows multinucleated giant cells. Most appropriate step?

A 27-year-old with papulovesicles and intense itch on finger webs/penile shaft; pink-brown nodules on scrotum persist after therapy. Management for nodules?

A 31-year-old with tender red nodules on shins (panniculitis), recent sore throat, and arthralgia. Most likely diagnosis/next step?

A 47-year-old presents with an enlarging boggy plaque with broken hairs and pustules on the scalp; KOH positive for dermatophyte. Best treatment?

A 60-year-old immunosuppressed patient develops painful necrotic eschars in beard area after “barber shave.” KOH shows hyphae invading follicles. Diagnosis/therapy?

A 25-year-old with grouped vesicles on an erythematous base on the lip border; precipitated by sun. Best acute and preventive strategy?

A 19-year-old student with painful dark necrotic papules on trunk/extremities, arthralgia, and tenosynovitis. Likely diagnosis/therapy?

A 33-year-old returns from Mediterranean trip with fever, headache, and maculopapular rash plus black eschar at bite site (“tache noire”). Likely disease/therapy?

A 54-year-old with a non-healing verrucous plaque at prior BCG vaccination site; biopsy: granulomas with caseation; culture positive for M. tuberculosis. Diagnosis?

A 42-year-old with multiple hyperpigmented macules with fine scale on trunk; KOH is negative after recent azole use. Best confirmatory test now?

A 30-year-old with intensely pruritic, serpiginous, rapidly moving linear rash on buttock after camping in Thailand. Most likely and therapy?

A 62-year-old with vesicular eruption on ear (concha) plus facial palsy and ear pain. Diagnosis/initial step?

A 36-year-old HIV+ with pruritic papulopustular eruption on face/forehead; KOH negative, responds to topical ivermectin. Diagnosis?

A 58-year-old with hand-foot-mouth disease exposure develops tender hemorrhagic vesicles on fingers and oral ulcers; Coxsackie A6 confirmed. Best management?

A 27-year-old with a painless papule that ulcerates and forms a black eschar after rabbit exposure; regional nodes enlarged. Diagnosis/therapy?

A 70-year-old with linear burrows on the scalp/face and crusting due to cognitive impairment. Diagnosis and best therapy?

A 45-year-old with thick brown-black non-scaly patch on the palm; KOH shows pigmented yeast. Diagnosis/therapy?

A 33-year-old returns from Amazon with multiple intensely pruritic bites that swell and persist on exposed legs; no burrows. Most likely and step?

A 52-year-old with chronic scalp scaling and broken hairs; Wood’s lamp shows bright green fluorescence. Likely organism/treatment?

A 61-year-old with chronic onychomycosis asks about liver safety. Correct counseling?

A nurse develops a throbbing, tender vesicular lesion around the distal finger after caring for a patient with HSV. Best management?

A 5-year-old has a bright red, sharply demarcated perianal rash with pain on defecation and blood-streaked stools. Rapid strep test positive. Best therapy?

An HIV patient (CD4 80) has multiple friable, violaceous papules and nodules resembling “angiomas” on face/arms. Biopsy: vascular proliferation with bacilli on Warthin–Starry. Best treatment?

A traveler from rural West Africa presents with a painless undermined ulcer on the calf; biopsy shows mycolactone-mediated necrosis; PCR positive for M. ulcerans. Therapy?

A 32-year-old with a draining submandibular sinus overlying matted cervical nodes; CXR shows apical cavitation; biopsy: granulomas with caseation. Diagnosis/management?

After ocean swimming in Florida, a 20-year-old develops intensely pruritic papules confined under the swimsuit; onset within hours. Best step?

A camper develops intensely itchy papules within hours of lake exposure on thighs and torso sparing covered areas. Likely cause/management?

A collegiate wrestling team has clustered painful facial/neck vesicles; one athlete febrile. Best team-level measure?

A 61-year-old asks about shingles prevention. He had chickenpox in childhood. Best vaccine counseling?

A 70-year-old with healed thoracic shingles now has severe burning pain for months. First-line options?

A febrile 2-day-old infant develops diffuse tender erythema and flaccid bullae with positive Nikolsky sign; mucosa spared. Best management?

Patient with recurrent MRSA skin abscesses asks about prevention. Evidence-based decolonization?

A 24-year-old from the Amazon has gritty black concretions encasing scalp hairs; microscopy shows dematiaceous fungal nodules cementing the shaft. Best treatment?

A man with malodor and yellow concretions on axillary hair; Wood’s lamp shows yellow fluorescence. Most appropriate step?

A child from the Pacific develops concentric polycyclic scaly rings over trunk; siblings affected. Diagnosis/therapy?

A 40-year-old with painful maceration at mouth angles; KOH shows yeast and fissuring. Best treatment?

An HIV+ patient has white corrugated lateral tongue plaques that do not scrape off; asymptomatic. Best management?

A 32-year-old with creamy white oral plaques that scrape off leaving erythema; HIV negative, recent antibiotics. First-line?

A painless indurated genital ulcer with clean base and firm edges appears 3 weeks after unprotected sex; painless nodes present. Treatment?

A 28-year-old with diffuse non-pruritic papulosquamous rash involving palms/soles and “mucous patches” in mouth. Next step?

A 23-year-old with multiple anogenital warts, immunocompetent, desires self-applied therapy. Best option?

A 29-year-old with numerous genital molluscum contagiosum lesions. Appropriate counseling/management?

A healthy adult with common warts on hands asks about the most evidence-based home therapy.

Multiple recalcitrant warts on knees in an adult after failure of cryotherapy. Next option?

Painful periungual warts threaten nail matrix. Best approach?

A 6-year-old with bright “slapped-cheek” rash then lacy exanthem on trunk; otherwise well. Diagnosis?

A febrile adult with cough, conjunctivitis, Koplik spots, then morbilliform rash from head to toe. Management?

A young woman with low-grade fever, posterior auricular lymphadenopathy, and fine maculopapular rash. She is 10 weeks pregnant. Best action?

A 28-year-old nonimmune pregnant woman had close contact with a child with chickenpox. Best prophylaxis?

A cat bite to the hand 8 hours ago shows puncture wounds, mild erythema, no abscess. Best empiric therapy?

A 20-year-old with tender axillary nodes after kitten scratch; small papule at site. Best management?

A homeless man has chronic necrotic ulcers with gray membrane on legs; culture grows toxigenic Corynebacterium diphtheriae. Best step?

A child with fever, sore throat, and diffuse erythematous “sandpaper” rash with strawberry tongue. Treatment?

A tampon user presents with fever, hypotension, diffuse erythematous rash including palms/soles; labs show multi-organ involvement. Next step?

A 26-year-old with intense pubic itching; exam shows blue-gray macules (maculae ceruleae) and attached insects on hair. Management?

A man with body lice infestation and pruritic seams on clothing; febrile with headache. Concern and step?

A 7-year-old with head lice failed permethrin. Evidence-based next options?

A 28-year-old adult with inflammatory tinea capitis (kerion) from T. tonsurans. Optimal therapy?

A 3-month-old infant with scabies has facial/scalp papules and severe itch. Preferred regimen?

A 35-year-old from Brazil has chronic ulcerative nasal/oral lesions after a prior cutaneous ulcer on the leg. Likely organism and therapy?

A 63-year-old cirrhotic man develops hemorrhagic bullae and sepsis after a cut sustained while shucking oysters. Best empiric therapy?

A 44-year-old with freshwater laceration develops rapidly progressive cellulitis; culture later shows Aeromonas hydrophila. Initial empiric coverage should have included?

A 35-year-old returns from a safari with a painful chancre at a tsetse bite site and fever. Skin finding suggests?

A 52-year-old gardener with a verrucous, crusted plaque on forearm; biopsy: broad-based budding yeasts. Best therapy?

A 61-year-old with fever, severe headache, and petechial rash starting at wrists/ankles spreading to trunk; tick exposure in spring. Best immediate therapy?

A 28-year-old asplenic patient develops fulminant sepsis 24 hours after a dog bite. Likely pathogen and empiric therapy?

A 40-year-old woman after “fish pedicure” develops furuncle-like nodules; culture grows rapidly growing mycobacteria. Most likely organism/therapy?

A 33-year-old had cosmetic filler injections; weeks later, indurated nodules appear; biopsy: “cording” granulomas with AFB-negative initially; culture later RGM. Best step?

A 29-year-old refugee presents with multiple papillomatous ulcers on lower limbs; dark-field negative; endemic tropical region. Likely diagnosis and therapy?

A 36-year-old from rural Latin America with blue-black plaques that later hypopigment/depigment (carate). Likely entity and treatment?

A 27-year-old develops severe cellulitis after a clenched-fist injury (“fight bite”). Best empiric antibiotic?

A 58-year-old with painful necrotic ulcer and surrounding violaceous undermined border is suspected to have pyoderma gangrenosum; cultures negative. Appropriate initial action?

A 34-year-old with scabies started on high-dose steroids for asthma develops Gram-negative sepsis and serpiginous perianal tracks. Concern?

Before initiating high-dose steroids in a migrant from Southeast Asia with eosinophilia, what screen prevents deadly complication?

A 22-year-old MSM presents with fever, lymphadenopathy, and deep-seated vesiculopustular lesions with central umbilication on genitals and perianal pain. Likely diagnosis/first-line?

A 31-year-old with classic bullous impetigo asks how it differs from SSSS. Correct statement?

A 48-year-old with chronic tinea pedis and onychomycosis develops erysipelas. Most impactful preventive measure?

A 26-year-old with genital ulcers that are painful, shallow, and recurrent with tender nodes; PCR positive for HSV-2. Counseling/treatment?

A 59-year-old with verrucous draining plaque on dorsal foot; grains are black; culture shows Madurella spp. Best management?

A 32-year-old with tender red nodules on shins after valley fever diagnosis. The nodules likely represent?

A 45-year-old dairy worker develops a violaceous, firm nodule on hand after milking; similar to orf but in cattle. Diagnosis?

A 70-year-old with shingles asks about antiviral timing. Best advice?

A 25-year-old with suspected Lyme disease asks about rash appearance. Accurate description?

A 32-year-old with chronic interdigital maceration, malodor, and coral-red fluorescence in toe webs. Diagnosis and treatment?

A 50-year-old with immunosuppression develops numerous disseminated molluscum lesions. First priority?

A 41-year-old with thickened, anesthetic hypopigmented plaques and marked neuritis during MDT for leprosy; no systemic symptoms. Reaction type/management?

A 23-year-old with painful clustered vesicles on the finger pulp; co-worker suggests I&D. Appropriate advice?

A 58-year-old with diabetic foot infection has green, malodorous discharge and colonized nails. Besides antibiotics/debridement, what local measure helps?

A 7-year-old with tinea capitis and household cat with alopecia. Best adjunct to systemic therapy?

A 62-year-old with zoster ophthalmicus has tip-of-nose vesicles (Hutchinson sign). Why urgent ophthalmology?

A 30-year-old with MRSA furuncles asks about bleach baths for prevention. Proper guidance?

A 54-year-old with perioral crusted lesions; bacterial culture positive for MSSA; mupirocin failure. Next reasonable step?

A 46-year-old with chronic interdigital tinea pedis and onychomycosis wants an alternative to continuous terbinafine. Option?

After a freshwater lake swim, a patient develops papulopustular folliculitis on buttocks; culture: Pseudomonas. Management?

A 39-year-old on long-term antibiotics for acne develops fullness/tenderness in submandibular area and malodorous draining tract from lower molar. Diagnosis/treatment?

A 21-year-old with painful perianal ulcers and tender suppurative nodes; Gram stain from lesion shows small Gram-negative coccobacilli; STI exposure. Likely and therapy?

A 33-year-old diver with puncture wound from sea urchin now has persistent granulomatous nodules; X-ray shows retained spines. Best management?

A 42-year-old has expanding annular erythema with central clearing after hiking; no systemic symptoms. Best diagnostic approach?

A 24-year-old bitten by a stray dog on the calf; never vaccinated for rabies. Best PEP regimen?

A 58-year-old immunosuppressed patient with fever and umbilicated papules on face/trunk; biopsy: yeast with narrow-based budding in histiocytes. Likely diagnosis/therapy?