ABD - American Board of Dermatology Dermatopathology Questions and Answers

Question 1

A 45-year-old man presents with a slowly growing, firm, flesh-colored nodule on his scalp. Histopathologic examination reveals a well-circumscribed, non-encapsulated dermal neoplasm composed of nests and cords of basaloid cells. The nests exhibit peripheral palisading and are embedded in a prominent, hyalinized, eosinophilic stroma. Notably, there are two distinct populations of basaloid cells and small duct-like structures. Which of the following is the most likely diagnosis?

Accepted Answer

Cylindroma

Answer

The histopathologic features described, particularly the 'jigsaw' or 'mosaic' pattern of basaloid cell nests within a hyalinized stroma, are classic for a cylindroma. The presence of two cell populations and ductal differentiation are also characteristic features. While trichoepithelioma and basal cell carcinoma are in the differential for basaloid neoplasms, they do not typically exhibit the prominent hyalinized stroma and jigsaw puzzle appearance. Spiradenomas are composed of two cell types but typically form well-defined nodules in the deep dermis or subcutis and can be painful.

Question 2

A biopsy of a skin lesion from a patient with suspected graft-versus-host disease (GVHD) is examined. Which of the following constellations of findings would be most characteristic of acute cutaneous GVHD?

Accepted Answer

Apoptotic keratinocytes (satellite cell necrosis) at all levels of the epidermis and a vacuolar interface dermatitis

Answer

The hallmark of acute cutaneous graft-versus-host disease is a vacuolar interface dermatitis accompanied by lymphocytic infiltration and, most critically, evidence of keratinocyte injury in the form of apoptosis. Apoptotic keratinocytes, sometimes surrounded by lymphocytes (satellite cell necrosis), are a key feature. Hyperkeratosis and a dense band-like infiltrate are more typical of lichen planus. A subepidermal blister with eosinophils suggests bullous pemphigoid, and nodular lymphoid aggregates suggest cutaneous lymphoid hyperplasia or lymphoma.

Question 3

A 60-year-old woman has a pearly papule on her nose. A shave biopsy shows nests of basaloid cells with peripheral palisading, scant cytoplasm, and a surrounding fibromyxoid stroma with retraction artifact. An immunohistochemical stain is performed. Which of the following stains would most strongly and diffusely support the diagnosis?

Accepted Answer

Ber-EP4

Answer

The clinical and histologic description is classic for basal cell carcinoma (BCC). Ber-EP4 is an antibody that recognizes the Epithelial Cell Adhesion Molecule (EpCAM) and is a highly sensitive and specific marker for BCC, staining it strongly and diffusely. It is particularly useful in distinguishing BCC from trichoepithelioma, which is typically negative or only focally positive. S-100 and Melan-A are melanocytic markers. Cytokeratin 20 is characteristically positive in Merkel cell carcinoma in a perinuclear dot-like pattern, but not in BCC.

Question 4

Which of the following is the defining histopathologic feature used to classify a blistering disease as 'pemphigus'?

Accepted Answer

Acantholysis leading to an intraepidermal split

Answer

The term 'pemphigus' refers to a group of autoimmune blistering diseases characterized by acantholysis, which is the loss of intercellular connections between keratinocytes. This loss of adhesion results in an intraepidermal blister. The level of the split (e.g., suprabasal in pemphigus vulgaris, subcorneal in pemphigus foliaceus) can vary, but acantholysis is the common pathogenic mechanism and defining histologic feature. Subepidermal splits are seen in diseases like bullous pemphigoid and dermatitis herpetiformis. Festooning is characteristic of porphyria cutanea tarda. Linear IgA deposition defines linear IgA bullous dermatosis.

Question 5

A biopsy of a verrucous plaque from the lower leg of an elderly diabetic patient shows pseudoepitheliomatous hyperplasia, a mixed inflammatory infiltrate with neutrophils forming microabscesses, and small, round, copper-colored sclerotic bodies, some of which are undergoing septation. What is the most likely diagnosis?

Accepted Answer

Chromoblastomycosis

Answer

The presence of pseudoepitheliomatous hyperplasia with neutrophilic abscesses is a common reaction pattern to deep fungal infections. The key diagnostic finding described is the 'copper penny' or sclerotic body (also known as a Medlar body), which is pathognomonic for chromoblastomycosis. These are pigmented, thick-walled, round fungal forms that may show internal septations. Blastomycosis shows broad-based budding yeast, coccidioidomycosis presents as large spherules containing endospores, and histoplasmosis is characterized by small intracellular yeasts within macrophages.

American Board of Dermatology (ABD) Practice Test

American Board of Dermatology (ABD) Practice Test

ABD - American Board of Dermatology Dermatopathology Questions and Answers