CAQ-Derm key terms

Loss of cohesion between keratinocytes due to breakdown of desmosomes, leading to intraepidermal clefts or blisters. Seen in pemphigus vulgaris, Hailey-Hailey disease, and Darier disease.

Pinpoint bleeding that occurs when scale is removed from a psoriatic plaque, caused by dilated capillaries in the dermal papillae. It is a clinical clue to psoriasis.

Development of new skin lesions at sites of trauma or injury in individuals with certain skin diseases, classically psoriasis, lichen planus, and vitiligo. Also called isomorphic response.

Separation of the upper epidermis with gentle lateral pressure, indicating intraepidermal blistering. Positive in pemphigus vulgaris and toxic epidermal necrolysis, negative in bullous pemphigoid.

An intensely pruritic, vesicular eruption on extensor surfaces associated with gluten-sensitive enteropathy. Direct immunofluorescence shows granular IgA deposits at the dermal papillae.

An autoimmune blistering disease caused by IgG antibodies against desmoglein 1 and 3, producing flaccid intraepidermal blisters and mucosal erosions. Direct immunofluorescence shows intercellular IgG deposition.

An autoimmune subepidermal blistering disease with tense bullae, caused by IgG antibodies against hemidesmosomal proteins BP180 and BP230. Direct immunofluorescence shows linear IgG and C3 along the basement membrane.

A cell-cell adhesion structure that connects keratinocytes by linking intermediate filaments to the plasma membrane. Autoantibodies against desmosomal proteins cause acantholysis in pemphigus.

A structure that anchors basal keratinocytes to the underlying basement membrane by connecting intermediate filaments to laminin and collagen. Autoantibodies against hemidesmosomal antigens cause bullous pemphigoid.

A laboratory test that detects antibodies or complement deposited in a patient's skin biopsy using fluorescent-labeled antisera. It is essential for diagnosing autoimmune blistering diseases and lupus.

A chronic immune-mediated inflammatory skin disease characterized by well-demarcated erythematous plaques with silvery scale, commonly on extensor surfaces. It is associated with arthritis and metabolic syndrome.

An inflammatory disease affecting skin and mucous membranes, presenting with pruritic, purple, polygonal, planar papules. Oral lesions appear as white lacy plaques, and skin lesions may koebnerize.

Fine white lines forming a reticulated pattern on the surface of lichen planus lesions, especially on mucous membranes. They are a helpful diagnostic clue.

A severe, life-threatening mucocutaneous reaction, usually drug-induced, causing widespread epidermal detachment and mucosal erosions. It is characterized by full-thickness epidermal necrosis and a positive Nikolsky sign.

A severe mucocutaneous reaction, often drug-induced, with epidermal detachment involving less than 10% of body surface area. It is distinguished from toxic epidermal necrolysis by the extent of detachment.

A malignant neoplasm arising from melanocytes, often from a preexisting nevus or de novo. Key prognostic features include Breslow thickness, ulceration, and mitotic rate.

The vertical depth of melanoma invasion measured from the granular layer of the epidermis to the deepest tumor cell, in millimeters. It is the most important prognostic factor for localized melanoma.

A mnemonic for melanoma warning signs: Asymmetry, Border irregularity, Color variation, Diameter greater than 6 mm, and Evolution or change. It aids in early detection.

The most common skin cancer, arising from basal keratinocytes and locally destructive but rarely metastatic. It presents as a pearly papule with telangiectasia, often on sun-exposed skin.

A malignant tumor of keratinocytes that may arise from actinic keratosis or de novo, with potential for metastasis. It often presents as a scaly, crusted, or ulcerated nodule on sun-damaged skin.

A precancerous lesion of the epidermis caused by chronic ultraviolet exposure, presenting as a rough, scaly macule on sun-exposed skin. It may progress to squamous cell carcinoma.

A chronic, pruritic inflammatory skin disease with a relapsing course, often starting in childhood and associated with atopy. It features impaired skin barrier function and eczematous lesions.

A protein essential for skin barrier formation by aggregating keratin filaments and contributing to the cornified envelope. Loss-of-function mutations are a major risk factor for atopic dermatitis.

A disseminated herpes simplex virus infection complicating atopic dermatitis, presenting as monomorphic punched-out vesicles or erosions. It is a medical emergency requiring antiviral therapy.

An inflammatory skin reaction caused by direct contact with an irritant or allergen, presenting as erythema, vesicles, or scaling. It is classified as irritant or allergic.

A diagnostic procedure for allergic contact dermatitis in which allergens are applied to the skin under occlusion and read at 48 and 72–96 hours. It detects delayed-type hypersensitivity.

A delayed, T-cell-mediated immune reaction that peaks 48–72 hours after antigen exposure. It underlies allergic contact dermatitis and is detected by patch testing.

A vascular reaction of the skin characterized by transient, pruritic wheals and sometimes angioedema, caused by histamine release from mast cells. Individual lesions resolve within 24 hours.

A form of physical urticaria in which stroking the skin produces a linear wheal within minutes. It is caused by mast cell degranulation and is usually idiopathic.

An acute, self-limited mucocutaneous eruption characterized by target lesions, often triggered by infections such as herpes simplex. It is distinct from Stevens-Johnson syndrome.

A skin lesion with three concentric zones: a dusky center, a pale ring, and an erythematous halo. It is characteristic of erythema multiforme.

A panniculitis presenting as tender, erythematous nodules on the shins, often associated with streptococcal infection, sarcoidosis, or inflammatory bowel disease. It is a delayed hypersensitivity reaction.

Inflammation of the subcutaneous fat, presenting as tender nodules or plaques. It can be classified as septal or lobular and may be associated with systemic disease.

A dermatophyte infection of the glabrous skin, presenting as an annular, scaly plaque with central clearing and an active border. Diagnosis is confirmed by KOH microscopy or culture.

A bedside microscopic examination in which potassium hydroxide dissolves keratin, allowing visualization of fungal hyphae or spores. It is used to diagnose dermatophyte infections.

A group of fungi that infect keratinized tissues such as skin, hair, and nails, causing tinea infections. Common genera include Trichophyton, Microsporum, and Epidermophyton.

An infestation by the mite Sarcoptes scabiei, causing intense pruritus and a papulovesicular rash, often with burrows in web spaces. It is highly contagious and treated with topical permethrin or oral ivermectin.

A linear, thread-like tunnel in the stratum corneum created by the scabies mite, often ending in a tiny vesicle. It is a hallmark clinical sign of scabies.

A chronic inflammatory disorder of the pilosebaceous unit characterized by comedones, papules, pustules, and nodules, typically on the face and trunk. It is driven by follicular hyperkeratinization, sebum, and Cutibacterium acnes.

A plug of keratin and sebum within a hair follicle, either open (blackhead) or closed (whitehead). Comedones are the primary lesion of acne vulgaris.

A systemic retinoid used for severe or refractory acne, which reduces sebum production and normalizes follicular keratinization. It is highly teratogenic and requires pregnancy prevention programs.