Dermatology MCQ - Infiltrative and Neoplastic Disorders - Inverted follicular keratosis

A 45-year-old man presents with a solitary, firm, 5-mm, skin-colored papule on his upper lip that has been slowly enlarging for over a year. The lesion is asymptomatic. On close inspection, it appears to have a slightly papillomatous surface. The most likely diagnosis and the corresponding definitive management is:

A. Basal cell carcinoma; perform Mohs micrographic surgery.
B. Viral wart; treat with cryotherapy.
C. Intradermal melanocytic nevus; observe with serial photography.
D. Inverted follicular keratosis; perform a shave or excisional biopsy for diagnosis and cure.
E. Sebaceous hyperplasia; treat with light electrocautery.

Correct Answer: D. Inverted follicular keratosis; perform a shave or excisional biopsy for diagnosis and cure.

Answer and Explanation

The correct answer is D. This question describes a classic presentation of an inverted follicular keratosis (IFK). The key clues are the location (head and neck, particularly the upper lip and cheek), the slow growth, and the appearance as a firm, skin-colored, sometimes papillomatous papule or nodule. IFK is a benign tumor of follicular origin. Because it is a diagnosis made upon histopathology and its clinical appearance can mimic other entities, a biopsy (shave or excision) is both diagnostic and curative.

Why the Other Options are Incorrect:

• A. Basal cell carcinoma (BCC): While BCC is common in this location, it often has a pearly appearance, telangiectasias, and may ulcerate. A firm, skin-colored, asymptomatic papule is less characteristic. A biopsy would distinguish them, but the most likely diagnosis for this specific description is IFK.

• B. Viral wart: Verruca vulgaris can have a papillomatous surface, but it is typically more verrucous (cauliflower-like) and may have black dots (thrombosed capillaries). It is unlikely to remain a simple, firm, skin-colored papule for over a year.

• C. Intradermal melanocytic nevus: This is a common diagnosis for a firm, skin-colored papule on the face. However, an intradermal nevus is typically dome-shaped and smooth, not papillomatous. While observation is reasonable for a classic nevus, the papillomatous surface should raise suspicion for other entities, warranting a biopsy.

• E. Sebaceous hyperplasia: This presents as a soft, yellowish, centrally umbilicated papule, not a firm, skin-colored, papillomatous one.

Additional High-Yield Information for Exams:

• Histopathology: This is the key to the diagnosis. IFK has a very characteristic microscopic appearance:

  • An endophytic (inverted) growth pattern into the dermis, forming well-circumscribed lobes.

  • Squamous eddies: Whorled nests of squamous cells are the hallmark feature.

  • Basaloid cells: The periphery of the lobules is composed of basaloid cells.

  • It is considered a variant of a benign follicular tumor (irritated seborrheic keratosis or a tumor of the follicular infundibulum).

• Differential Diagnosis: The clinical differential is broad, which is why biopsy is key. It includes:

  • Basal Cell Carcinoma

  • Keratoacanthoma (typically rapid growth with a central keratin crater)

  • Squamous Cell Carcinoma

  • Intradermal Nevus

  • Pyogenic Granuloma (if it has a history of bleeding)

• Prognosis: Excellent. Inverted follicular keratosis is a benign lesion. Simple excision is curative, and recurrence is rare.

• Management & Rationale:

  • Rationale: The goal is to obtain a definitive histological diagnosis to rule out malignancy (especially BCC and SCC) and to provide a cure.

  • First-line/Definitive Management: A shave or excisional biopsy. This procedure serves both to establish the diagnosis and to completely remove the lesion.

  • Monitoring: No specific long-term monitoring is required after complete excision.