ABPath Dermatopathology key terms

Loss of cohesion between keratinocytes caused by breakdown of intercellular attachments, producing rounded detached cells and clefts or blisters within the epidermis. It is the defining mechanism in pemphigus and several other blistering diseases.

Intercellular edema between keratinocytes that widens the spaces between cells and stretches desmosomes, giving the epidermis a pale, widened, fluid-filled appearance. It characterizes eczematous dermatitis and may progress to intraepidermal vesiculation.

A cluster of atypical lymphocytes collected within the epidermis, often surrounded by a clear halo, seen in mycosis fungoides. It reflects epidermotropism of neoplastic T cells and helps distinguish lymphoma from benign inflammatory dermatoses.

Migration of lymphocytes into the epidermis without prominent spongiosis, a pattern typical of cutaneous T-cell lymphoma. The cells may line up along the basal layer or form intraepidermal collections.

A narrow band of uninvolved superficial dermis separating the epidermis from a dense dermal infiltrate or deposit. Its presence suggests processes such as granuloma faciale, leprosy, or certain deposition disorders rather than a lichenoid interface reaction.

A pattern of band-like lymphocytic infiltration along the dermoepidermal junction with basal cell damage and apoptotic keratinocytes. It is seen in lichen planus, lichenoid drug eruptions, and interface dermatitis of lupus.

A dyskeratotic, eosinophilic apoptotic keratinocyte or fragment found at the dermoepidermal junction or in the papillary dermis. It is a hallmark of lichenoid interface dermatitis and is also called a colloid or cytoid body.

Premature or abnormal keratinization of individual keratinocytes, which become enlarged, eosinophilic, and often lose their nuclei. It occurs in squamous dysplasia, Bowen disease, and lichenoid reactions.

Separation of the epidermis just above the basal layer, leaving a row of basal cells attached to the basement membrane like tombstones. This pattern is characteristic of pemphigus vulgaris.

An autoimmune blistering disease caused by IgG antibodies against desmoglein 3, producing flaccid blisters and painful erosions. Histology shows suprabasal acantholysis, and direct immunofluorescence shows intercellular epidermal IgG.

A technique in which fluorochrome-labeled antibodies are applied to a patient's frozen tissue section to detect in situ deposits of immunoglobulin or complement. It is central to diagnosing autoimmune blistering diseases and vasculitis.

A subepidermal blistering disorder defined by linear deposition of IgA along the basement membrane zone on direct immunofluorescence. It may be idiopathic or drug-induced and shows neutrophil-rich subepidermal blisters.

Separation of the entire epidermis from the dermis at the basement membrane zone, producing a clean blister roof and floor. It is seen in bullous pemphigoid, epidermolysis bullosa acquisita, and other basement membrane disorders.

A laboratory preparation in which normal human skin is incubated in concentrated saline to cleave the basement membrane at the lamina lucida. The side on which immunofluorescence localizes helps distinguish bullous pemphigoid from epidermolysis bullosa acquisita.

A melanocyte differentiation antigen detected by immunohistochemistry in normal melanocytes and most melanomas. It is useful for confirming melanocytic lineage and for highlighting intraepidermal melanocytes in margin assessment.

A nuclear transcription factor expressed in melanocytes, Schwann cells, and myoepithelial cells. Its nuclear staining pattern makes it valuable for identifying melanoma and for distinguishing it from non-melanocytic mimics.

A calcium-binding protein expressed in melanocytes, neural crest derivatives, and some other tumors. It is a sensitive but not specific immunohistochemical marker for melanoma and neural lesions.

The measured depth of a melanoma from the granular layer of the epidermis to the deepest invasive tumor cell, expressed in millimeters. It is the strongest predictor of prognosis and guides staging and surgical margins.

A staging system describing melanoma invasion by anatomic layer: epidermis, papillary dermis, filling papillary dermis, reticular dermis, and subcutaneous fat. It has largely been supplanted by Breslow thickness.

Identification and removal of the first draining lymph node from a tumor bed using dye or radiotracer mapping. In melanoma it provides staging information for tumors above a defined thickness threshold.

Full-thickness atypia of the epidermis without invasion through the basement membrane, also called Bowen disease. It presents as a scaly plaque and carries risk of progression to invasive carcinoma.

A sun-induced lesion showing atypical keratinocytes confined to the lower portion of the epidermis, often with parakeratosis and solar elastosis. It is considered a precursor to squamous cell carcinoma.

Degeneration of dermal elastic tissue from chronic ultraviolet exposure, appearing as basophilic, tangled, thickened fibers in the upper dermis. It is a useful marker of sun-damaged skin in biopsy interpretation.

The most common cutaneous T-cell lymphoma, characterized by epidermotropic atypical T cells and a protracted patch, plaque, and tumor phase. Early lesions may mimic eczema, so clinicopathologic correlation and molecular studies are often needed.

A molecular test detecting clonal rearrangements of T-cell receptor genes to support a diagnosis of cutaneous T-cell lymphoma. A clonal result supports malignancy but must be interpreted with histology and clinical findings.

Dermal inflammation composed of organized collections of histiocytes, with or without giant cells and necrosis. Causes include infection, foreign material, sarcoidosis, and drug reactions, and special stains are often required.

A modified acid-fast stain used to detect mycobacteria, particularly Mycobacterium leprae, in tissue sections. It is more sensitive than the standard Ziehl-Neelsen stain for leprosy because it resists decolorization.

A histochemical stain that highlights carbohydrates such as fungal cell walls and basement membranes in magenta. It is widely used to screen for dermatophytes and yeasts in skin biopsies.

A silver-based histochemical stain that renders fungal walls black against a green background. It is used to detect fungi in tissue, including organisms that are sparse or poorly seen on routine stains.

A tissue section of known reactivity processed alongside the test slide to verify that staining reagents performed as expected. Positive and negative controls are essential for valid interpretation and laboratory quality assurance.

Rapid tissue processing in which unfixed tissue is frozen, sectioned, and stained for intraoperative interpretation. In dermatology it is used mainly for margin assessment in Mohs surgery or selected tumor excisions.

A staged excision technique in which the entire peripheral and deep margin of each layer is examined microscopically before further tissue is removed. It maximizes tissue conservation and margin control for skin cancers.

External assessment in which a laboratory analyzes unknown specimens and compares results with peer laboratories or a reference standard. It is a required component of quality assurance for accredited diagnostic laboratories.

The interval between specimen receipt or test ordering and reporting of the final result. It is a key performance indicator for laboratory operations and patient care quality.

The process of integrating clinical history, physical findings, and microscopic features to reach a diagnosis. It is especially important in dermatopathology, where many inflammatory diseases share overlapping histologic patterns.

An intensely pruritic blistering eruption associated with gluten-sensitive enteropathy, showing granular IgA deposits at the dermal papillae on direct immunofluorescence. Histology shows neutrophil microabscesses in dermal papillae.