Dermatology MCQ - Infiltrative and Neoplastic Disorders - Dermatosis papulosa nigra

A 35-year-old woman of Fitzpatrick skin type V presents for cosmetic consultation regarding multiple, small, dark brown to black papules that have been gradually appearing on her malar cheeks and temples over the past decade. The lesions are smooth, firm, and measure 1-4 mm in diameter. She is otherwise healthy. What is the most accurate statement regarding the nature and management of these lesions?

A. They are a form of seborrheic keratosis with a strong genetic predisposition in darker skin types; treatment with light electrodesiccation is effective but carries a risk of post-inflammatory dyspigmentation.
B. They are multiple verrucae plana caused by human papillomavirus; treatment with topical imiquimod is the first-line therapy.
C. They are an eruptive form of melanocytic nevi associated with hormonal changes; no treatment is recommended.
D. They are a sign of acanthosis nigricans and warrant screening for diabetes and metabolic syndrome.
E. They are a variant of trichoepitheliomas; treatment requires surgical excision.

Correct Answer: A. They are a form of seborrheic keratosis with a strong genetic predisposition in darker skin types; treatment with light electrodesiccation is effective but carries a risk of post-inflammatory dyspigmentation.

Answer and Explanation

The correct answer is A. This question describes the classic presentation of dermatosis papulosa nigra (DPN). The key clinical clues are the patient's skin type (Fitzpatrick IV-VI), the location on the face (malar cheeks, temples), and the description of multiple, small, hyperpigmented, smooth papules. DPNs are considered a variant of seborrheic keratosis that is very common and has a strong genetic predisposition in individuals with darker skin. Treatment is effective but must be undertaken with caution due to the high risk of post-inflammatory hyper- or hypopigmentation.

Why the Other Options are Incorrect:

• B. Multiple verrucae plana...: While flat warts can appear similar, they are typically more flat-topped, less pigmented (often skin-colored or tan), and are caused by HPV. They are not strongly associated with a specific genetic background in darker skin types. Imiquimod is not a standard treatment for DPN.

• C. An eruptive form of melanocytic nevi...: Melanocytic nevi are nests of melanocytes. DPNs are benign tumors of keratinocytes, like seborrheic keratoses. They are not hormonally driven in the same way, and their appearance over a decade is not considered "eruptive."

• D. A sign of acanthosis nigricans...: Acanthosis nigricans presents as velvety, hyperpigmented plaques in intertriginous areas (neck, axillae, groin), not as multiple, discrete papules on the face. While both occur in darker skin types, they are distinct entities.

• E. A variant of trichoepitheliomas: Trichoepitheliomas are benign tumors of hair follicle origin that are typically skin-colored, firm papules, often located on the central face. They are not characteristically hyperpigmented like DPNs.

Additional High-Yield Information for Exams:

• Histopathology: Identical to a seborrheic keratosis. It shows:

  • Hyperkeratosis, acanthosis, and papillomatosis.

  • Horn pseudocysts (inverted keratin plugs).

  • The main difference from a classic seborrheic keratosis is the prominent pigmentation in the basal layer, which accounts for the dark color clinically.

• Differential Diagnosis: The main clinical differential includes:

  • Seborrheic Keratosis: The same entity histologically, but the term DPN is used for the specific clinical presentation in darker skin types.

  • Verruca Plana (Flat Warts): As above.

  • Multiple Small Melanocytic Nevi: Can be distinguished by dermoscopy.

• Associated Conditions & Prognosis:

  • Genetics: There is a very strong autosomal dominant familial predisposition.

  • Prevalence: Increases with age; seen in up to 35% of the Black population.

  • Prognosis: Excellent. These are benign lesions with no malignant potential. They are a cosmetic concern only.

• Management & Rationale:

  • Rationale: The primary goal is cosmetic improvement while minimizing the risk of dyspigmentation, which is the most common complication of treatment.

  • First-line: Reassurance. Many patients do not desire treatment.

  • Treatment Options: If treatment is desired, modalities must be superficial to avoid scarring.

    • Light Electrodesiccation: Very effective, but must be performed with low power to avoid thermal damage to the surrounding melanocytes.

    • Light Cryotherapy: A very brief freeze time is used.

    • Carbon Dioxide or Erbium:YAG Laser: Provides precise ablation.

  • Crucial Counseling: Patients must be thoroughly counseled that treatment, while effective at removing the lesions, carries a significant risk of post-inflammatory hyperpigmentation or hypopigmentation, which can be more cosmetically noticeable than the original lesions. Test spots are often recommended.