Atopic dermatitis is most closely associated with which type of hypersensitivity reaction?
Options:
Type I (IgE-mediated)
Type II (antibody-mediated cytotoxicity)
Type III (immune complex-mediated)
Type IV (delayed, T-cell mediated)
Type V (stimulating autoantibody)
Type I (IgE-mediated)
Explanation:
AD is associated with elevated IgE levels and Th2 cytokines (IL-4, IL-5, IL-13).
Allergen exposure triggers IgE-mediated mast cell activation, leading to pruritus and inflammation.
Chronic lesions may have Th1 involvement, but the underlying hypersensitivity mechanism is Type I.
In older children and adults, atopic dermatitis most commonly affects which areas of the body?
Options:
Extensor surfaces (elbows, knees)
Flexor surfaces (antecubital and popliteal fossae) and face
Palms and soles
Trunk only
Scalp and neck only
Flexor surfaces (antecubital and popliteal fossae) and face
Explanation:
In infants, AD typically affects the face and extensor surfaces.
In older children and adults, lesions shift to the flexor surfaces (e.g., antecubital and popliteal fossae) and the face may still be involved.
Distribution is often symmetric, and chronic lesions show lichenification from scratching.
What type of hypersensitivity reaction is allergic contact dermatitis?
Options:
Type I (IgE-mediated)
Type II (antibody-mediated)
Type III (immune complex-mediated)
Type IV (T-cell mediated / delayed)
Type V (stimulating antibodies)
: Type IV (T-cell mediated / delayed)
Explanation:
Allergic contact dermatitis is a delayed hypersensitivity reaction.
Sensitization occurs on first exposure to the allergen, with T-cell mediated inflammation on re-exposure.
Which of the following is a common trigger for allergic contact dermatitis?
Nickel jewelry
Poison ivy/oak
Latex
Fragrances in cosmetics
All of the above
Back:
Answer: All of the above
A 17-year-old girl presents with severe nighttime genital itching and vulvar excoriations. Her sexual partner has similar symptoms. Microscopy of an epilated pubic hair shows a nit attached to the hair shaft. Which organism is most likely responsible?
Options:
Phthirus pubis
Pediculus humanus
Enterobius vermicularis
Epidermophyton floccosum
Sarcoptes scabiei
Phthirus pubis
Explanation:
Pediculosis pubis (crab lice) is caused by Phthirus pubis, a sexually transmitted parasite.
Presents with intense pruritus, worse at night, and excoriations in the pubic area.
Nits are attached to pubic hair shafts.
Condoms do not prevent transmission, as lice are spread by direct contact.
Pediculus humanus causes head or body lice; Enterobius causes perianal itching; Epidermophyton causes fungal infections; Sarcoptes causes scabies with burrows.
A 45-year-old man experiencing homelessness presents with a 1-week history of a red, itchy rash on his hands. The itching is worse at night and several shelter residents have similar symptoms. Physical exam shows linear burrows and excoriations. Which topical drug mechanism is most likely effective?
Binding to sodium channels
Inhibition of nuclear factor-κB
Decrease in peptidoglycan synthesis
Inhibition of histamine-1 receptors
Increase in keratinocyte turnover
Binding to ergosterol
Binding to sodium channels
Explanation:
The patient has scabies caused by Sarcoptes scabiei, transmitted via close contact.
Topical permethrin is first-line treatment.
Mechanism: Permethrin binds to sodium channels in the parasite’s nerve and muscle cells, causing delayed depolarization → paralysis and death.
A 30-year-old man presents with a 2-week history of well-demarcated, erythematous, scaly plaques on his elbows. No systemic illness or medications. Which is the most appropriate treatment?
Options:
Dapsone
Terbinafine
Ketoconazole
Calcipotriene
Diphenhydramine
Calcipotriene
Explanation:
The patient has mild plaque psoriasis: well-demarcated, erythematous plaques with silvery-white scale on extensor surfaces.
First-line treatment for mild disease: topical therapies such as calcipotriene (vitamin D analog) or corticosteroids.
Mechanism: Calcipotriene binds vitamin D receptor → promotes keratinocyte differentiation and inhibits proliferation.
Other options:
Dapsone: used for dermatitis herpetiformis (pruritic vesicles, celiac disease)
Terbinafine/Ketoconazole: antifungals, used for dermatophytes or seborrheic dermatitis
Diphenhydramine: antihistamine, only relieves itching
What is the mechanism of action of Calcipotriene?
Synthetic form of vitamin D used primarily to treat plaque psoriasis, helping to regulate skin cell growth and reduce scaling.
This patient’s tender blue-red lesion under the left thumbnail, with pain that worsens with exposure to cold temperatures, suggests a
Glomus tumors
Glomangiomas
A type of rare, benign neoplasm that originates from glomus bodies in the skin, which are involved in temperature regulation. Most commonly manifest as a singular, paroxysmally painful, blue-red soft mass in the subungual regions of the digits or the deep dermis of the palm, wrist, forearm, and foot.
Rash starts on face → spreads to trunk, postauricular & suboccipital lymphadenopathy, mild fever
Rubella (German measles) — Togavirus, ssRNA (+)
Rash starts on face → spreads slowly, Koplik spots, high fever, cough, coryza, conjunctivitis
Measles (Rubeola) — Paramyxovirus, ssRNA (-)
High fever for 3–5 days → fever breaks → maculopapular rash appears on trunk
Roseola (HHV-6/HHV-7)
Vesicular rash in different stages of healing, starts on trunk → spreads to face
Varicella-zoster virus (Chickenpox)
Painful grouped vesicles on an erythematous base
HSV-1 or HSV-2 (DNA virus)
Tender lymphadenopathy, rash resolves in 3 days, immigrant child, unimmunized
Rubella again — think MMR vaccine prevention
Complication of measles years later
Subacute sclerosing panencephalitis (SSPE)
A 19-year-old woman notices blue staining of her clothes after exercise and dark discoloration in her axillae, areolae, and perineum. Biopsy shows lipofuscin granules within coiled secretory glands in the lower dermis whose ducts empty into hair follicles.
Which term best describes these glands?
Answer choices:
A. Autocrine
B. Holocrine
C. Endocrine
D. Paracrine
E. Eccrine
F. Apocrine
F. Apocrine
F. Apocrine
🧩 Explanation:
Apocrine glands are sweat glands located in the axillae, areolae, perineum, and genital area.
They secrete a viscous, milky fluid into hair follicles and become active at puberty.
The secretions contain proteins, lipids, and steroids, and bacterial decomposition of these products causes odor or colored sweat stains (chromhidrosis).
Histologically, apocrine glands have large lumens and contain lipofuscin pigment within secretory cells.
Other gland types:
Which sweat glands are used for thermoregulation?
Eccrine glands.
What kind of secretion do eccrine glands use?
A: Merocrine (exocytosis).
: What activates eccrine glands?
A: Sympathetic cholinergic fibers (M3 receptors).
Where are apocrine glands located?
A: Axillae, areolae, perineum, and genital region.
Q: When do apocrine glands become active?
A: After puberty.
Q: Where do apocrine glands secrete?
A: Into the hair follicle.
Q: What condition causes colored sweat from apocrine glands?
A: Chromhidrosis (lipofuscin pigment in apocrine secretion).
