Dermatology MCQ - Infiltrative and Neoplastic Disorders - Warty dyskeratoma

A 60-year-old man presents with a solitary, 8-mm lesion on the scalp. It is a firm, reddish-brown papule with a central, keratotic plug. The patient reports it has been present for several months and is occasionally tender. A shave biopsy is performed. The pathologist's report describes a cup-shaped epidermal invagination filled with keratin, with numerous acantholytic cells and corps ronds in the suprabasal layers. What is the most likely diagnosis?

A. Actinic keratosis
B. Keratoacanthoma
C. Warty dyskeratoma
D. Pemphigus vulgaris
E. Hypertrophic lichen planus

Correct Answer: C. Warty dyskeratoma

Answer and Explanation

The correct answer is C. This question provides both a classic clinical description (solitary papule with a central keratotic plug on the head/neck of an older adult) and the pathognomonic histopathology of a warty dyskeratoma. The key histological terms are "cup-shaped invagination," "acantholytic cells" (discohesive keratinocytes), and "corps ronds" (rounded acantholytic cells with a condensed halo and a pyknotic nucleus). This combination is diagnostic for warty dyskeratoma.

Why the Other Options are Incorrect:

• A. Actinic keratosis: This is a pre-malignant lesion showing dysplasia of the keratinocytes, typically in a flat or slightly scaly plaque. It does not form a cup-shaped architecture and lacks the prominent acantholysis and corps ronds seen in warty dyskeratoma.

• B. Keratoacanthoma: This lesion is characterized by a rapidly growing, dome-shaped nodule with a central crater filled with keratin. Histologically, it shows a well-differentiated, glassy squamous proliferation with minimal atypia, but it does not typically feature the widespread acantholysis and corps ronds of warty dyskeratoma.

• D. Pemphigus vulgaris: This is an autoimmune blistering disease, not a tumor. While it shows acantholysis, it occurs at the suprabasal level and results in flaccid bullae and erosions on the skin and mucosa. It does not present as a solitary keratotic papule.

• E. Hypertrophic lichen planus: This presents as violaceous, hyperkeratotic plaques, often on the shins. Histology shows a dense, band-like lymphocytic infiltrate and a "saw-tooth" pattern of acanthosis, not acantholysis and corps ronds.

Additional High-Yield Information for Exams:

• Histopathology: The microscopic features are distinctive and must be recognized:

  • Cup-shaped / V-shaped epidermal invagination filled with a keratotic plug.

  • Suprabasal acantholysis (separation of keratinocytes just above the basal layer).

  • Villi: Dermal papillae lined by a single layer of basal cells projecting upward into the cavity.

  • Dyskeratotic cells: Specifically, corps ronds (in the granular layer) and grains (in the keratin plug).

• Differential Diagnosis: The clinical differential is broad, including other benign and malignant tumors with a central keratin plug, such as:

  • Keratoacanthoma

  • Hypertrophic Actinic Keratosis / Squamous Cell Carcinoma

  • Inverted Follicular Keratosis

  • Molluscum Contagiosum (though typically softer and with central umbilication, not a firm plug)

• Associated Conditions & Prognosis:

  • Benign Nature: Warty dyskeratoma is a benign epidermal tumor. It is considered a localized, focal form of the acantholytic dyskeratosis seen in Darier disease, but it is not associated with the systemic genetic mutation of that condition.

  • Prognosis: Excellent. It is cured by simple excision.

• Management & Rationale:

  • Rationale: The goal is to obtain a definitive diagnosis (as it can mimic malignancy) and provide a cure.

  • First-line/Definitive Management: Complete excision (e.g., shave excision with curettage or simple elliptical excision). This is both diagnostic and therapeutic.

  • Monitoring: No further action is needed after complete excision, as recurrence is rare.