EMREE - DFT - 13-10-2025 - Dermatology

A 34 Y/O M office worker presents with an intensely pruritic rash on his abdomen x2W. He reports the rash began shortly after purchasing a new belt. O/E, there is a well-demarcated, erythematous plaque with overlying papules and microvesicles in the periumbilical region. The rash's shape and location correspond precisely to where his new belt buckle rests against the skin. The rest of the cutaneous exam is unremarkable.What is the most likely diagnosis and its underlying immunological mechanism?

• Irritant contact dermatitis; Direct epidermal injury

• Atopic dermatitis; Type I IgE-mediated hypersensitivity

• Allergic contact dermatitis; Type IV delayed-type hypersensitivity

• Tinea corporis; Fungal proliferation in the stratum corneum

• Seborrheic dermatitis; Inflammatory reaction to Malassezia yeast

Answer explanation

The correct answer is Allergic contact dermatitis (ACD), which is a classic Type IV delayed-type hypersensitivity reaction. The vignette describes a textbook presentation of nickel allergy from a belt buckle. The key features are the localization and sharp demarcation of the eczematous rash to the area of contact with the allergen (the metal buckle) and the delay in onset (2 weeks). This type of reaction is T-cell mediated.

A 35 Y/O F c/o a pruritic, erythematous rash with scaling on her neck x10D. The rash has a linear and pendulous distribution corresponding to where she wears a new piece of metallic jewelry. O/E: Erythema, papules, and mild excoriations are noted in a defined pattern on the anterior neck. The patient has no Hx of atopy or psoriasis.What is the most appropriate next step in management?

• Prescribe oral terbinafine

• Advise application of petrolatum jelly and observation

• Perform a skin biopsy for histopathology

• Recommend avoidance of the trigger and prescribe a topical corticosteroid

• Initiate a course of oral prednisone

Answer explanation

The history and presentation are highly suggestive of allergic contact dermatitis. The cornerstone of management is twofold: (1) identification and avoidance of the offending allergen (the jewelry) and (2) suppression of the localized inflammation with a topical corticosteroid (e.g., mid-potency like triamcinolone).

A 4th-year medical student is on a dermatology rotation and is asked by the attending physician to identify the primary lesion associated with several common skin conditions. Which of the following options correctly pairs the primary dermatologic lesion with its representative disease?

• Vesicle - Psoriasis; Plaque - Urticaria; Wheal - Herpes zoster; Bulla - Bullous pemphigoid

• Vesicle - Herpes zoster; Plaque - Bullous pemphigoid; Wheal - Psoriasis; Bulla - Urticaria

• Vesicle - Herpes zoster; Plaque - Psoriasis; Wheal - Urticaria; Bulla - Bullous pemphigoid

• Vesicle - Urticaria; Plaque - Psoriasis; Wheal - Bullous pemphigoid; Bulla - Herpes zoster

Answer explanation

This option makes all correct associations. Vesicles (<1 cm fluid-filled blisters) are characteristic of herpes zoster (shingles). Plaques (raised, flat-topped lesions >1 cm) are the hallmark of psoriasis. Wheals (transient, edematous papules/plaques) are the primary lesion of urticaria. Bullae (>1 cm fluid-filled blisters) are pathognomonic for bullous pemphigoid.

A 35 Y/O hairdresser presents with a chronic, fissured hand rash x8mo, unresponsive to topical steroids. O/E: Lichenified, erythematous plaques on the dorsal hands. Her work involves constant exposure to hair dyes and chemicals. No Hx of atopy.What is the most appropriate Ix to identify the causative agent?

• Skin prick testing

• Serum total IgE

• Patch testing

• Skin biopsy

• RAST test

Answer explanation

Patch testing is the gold standard for identifying specific allergens causing allergic contact dermatitis (Type IV reaction), which is highly suspected given her occupation and chronic, localized rash.

34 Y/O M photographer c/o hypopigmented forearm patches appearing after darkroom work. Hx: transient, scaly red papules precede the white marks. Flares occur after eating shellfish. Positive family Hx of atopy. O/E: >8 small, ill-defined hypopigmented macules on bilateral dorsal forearms.What is the most likely diagnosis?

• Chemical leukoderma

• Pityriasis alba

• Psoriasis

• Vitiligo

• Tinea versicolor

Answer explanation

This question tests diagnostic acumen based on a mixed clinical picture. The key is the evolution of the lesions: transient scaly red papules resolving into hypopigmented marks is classic for post-inflammatory changes in psoriasis. The shellfish trigger is also a known flare factor.

A 35-year-old male presents with an itchy rash on his elbows and knees that has been present for 6 months. On examination, there are well-demarcated, red plaques covered with silvery scales. When a scale is removed, pinpoint bleeding occurs (positive Auspitz sign). Examination of his mouth reveals the oral mucosa is clear.What is the most likely diagnosis?

• Lichen Planus

• Pemphigus Vulgaris

• Psoriasis Vulgaris

• Atopic Dermatitis

Answer explanation

The combination of well-demarcated plaques with silvery scales on extensor surfaces, a positive Auspitz sign, and the absence of oral lesions is the classic presentation of Psoriasis Vulgaris.

A 24 Y/O M c/o an intensely itchy rash on his chest and back x3D. Hx reveals he frequently uses a hot tub at his gym after workouts. O/E: Multiple, discrete, erythematous follicular papules and pustules are noted across the chest and upper back. No comedones are present. Vitals are stable, and he is afebrile.What is the most likely causative organism?

• Staphylococcus epidermidis

• Pseudomonas aeruginosa

• Malassezia furfur

• Streptococcus pyogenes

• Candida albicans

Answer explanation

 The combination of folliculitis and recent hot tub use is classic for Pseudomonas aeruginosa folliculitis ("hot tub folliculitis"). This organism thrives in warm, aquatic environments and is the most common cause in this specific clinical context.

A 34 Y/O F with moderate papulopustular perioral dermatitis shows no improvement after 4 weeks of topical metronidazole and complete cessation of all facial creams. The rash remains inflamed and distressing to the patient.What is the most appropriate next step in Rx?

• Oral prednisolone

• Oral doxycycline

• Topical clindamycin

• High-potency topical tacrolimus

Answer explanation

 For moderate-to-severe perioral dermatitis, or cases refractory to initial topical therapy, a course of an oral tetracycline-class antibiotic like doxycycline or minocycline is the standard second-line treatment. They are used for their anti-inflammatory properties.

A 68 Y/O F presents to the clinic c/o a painful rash on her L forearm x3D. The rash was preceded by a 2-day Hx of intense burning & tingling in the same area. O/E, vitals are stable. Examination of the L arm reveals clusters of vesicles on an erythematous base. The lesion is arranged in a linear, band-like distribution that extends from the forearm to the index and middle fingers and does not cross the midline.What is the most likely Dx?

• Allergic contact dermatitis

• Herpes zoster

• Bullous impetigo

• Herpes simplex virus

• Dermatitis herpetiformis

Answer explanation

Herpes zoster (shingles) is the classic presentation. It is caused by the reactivation of the varicella-zoster virus and is characterized by a prodrome of neuropathic pain (burning, tingling) followed by the eruption of a unilateral, dermatomal vesicular rash on an erythematous base. The distribution described is consistent with the C7 dermatome.

21 Y/O M c/o a perioral rash x4D. Hx reveals the lesions began as small vesicles that ruptured. O/E, there are multiple golden, "honey-crusted" lesions on an erythematous base around his mouth. He is afebrile.What is the most likely Dx?

• Herpes simplex labialis

• Allergic contact dermatitis

• Impetigo contagiosa

• Angular cheilitis

• Staphylococcal scalded skin syndrome

Answer explanation

The pathognomonic finding of "honey-crusted" lesions on an erythematous base is classic for non-bullous impetigo contagiosa. The progression from vesicles to crusted lesions is the typical course for this superficial bacterial skin infection.