Dermatology MCQ - Infiltrative and Neoplastic Disorders - Ink-spot lentigo

A 25-year-old woman with Fitzpatrick skin type II presents for a routine examination. She is an avid hiker and is concerned about a solitary, intensely black, lesion on her shoulder. It has been present and unchanged for several years. On examination, the lesion is a 4-mm macule with a very dark, almost star-burst or irregular "ink-spot" appearance, but otherwise well-defined borders. Dermoscopy reveals a prominent, dark, pigmented network that appears strikingly black against the surrounding skin. What is the most appropriate clinical approach to this lesion?

A. Reassurance and periodic monitoring, as its clinical and dermoscopic appearance is pathognomonic for a benign lesion.
B. Immediate full-thickness excision with a 2-mm margin due to high suspicion for nodular melanoma.
C. Application of a high-potency topical corticosteroid twice daily for 2 weeks to treat suspected post-inflammatory hyperpigmentation.
D. Prescription of a topical imiquimod cream to stimulate a local immune response against potentially atypical cells.
E. Shave biopsy to confirm the diagnosis, as its appearance is indistinguishable from a severely dysplastic nevus.

Correct Answer: A. Reassurance and periodic monitoring, as its clinical and dermoscopic appearance is pathognomonic for a benign lesion.

Answer and Explanation

The correct answer is A. This question describes a classic ink-spot lentigo (also known as a reticulated black solar lentigo). The key to this question is recognizing that despite its alarmingly dark and irregular color, its specific clinical and dermoscopic features are highly characteristic of a benign process. The history of being stable for years in a sun-exposed individual is also reassuring.

The dermoscopic description of a "prominent, dark, pigmented network" that is uniform in its pattern, though very dark, is the hallmark. The "ink-spot" or "starburst" appearance is due to the extreme hyperpigmentation within an otherwise typical solar lentigo structure.

Why the Other Options are Incorrect:

• B. Immediate full-thickness excision... for nodular melanoma: This is incorrect and represents an over-management. Nodular melanoma is typically raised (a nodule), and the lesion described is a macule. The history of long-term stability is also strongly against a malignant process.

• C. Application of a high-potency topical corticosteroid... for post-inflammatory hyperpigmentation: This is incorrect and potentially harmful, causing atrophy. Post-inflammatory hyperpigmentation follows a history of inflammation (e.g., acne, eczema) and does not have the specific reticulated network seen here.

• D. Prescription of topical imiquimod...: This is incorrect and not indicated. Imiquimod is used for certain neoplastic conditions (e.g., superficial basal cell carcinoma, actinic keratosis). There is no role for it in managing a benign lentigo.

• E. Shave biopsy to confirm the diagnosis...: While a biopsy would provide a definitive diagnosis, it is not the most appropriate first step. Given the highly characteristic features, the standard of care is recognition and monitoring. Unnecessary biopsies on benign, pathognomonic lesions should be avoided. If there is any doubt or if the patient is anxious, a biopsy is reasonable, but reassurance is the primary and most correct approach.

Additional High-Yield Information for Exams:

• Histopathology: Similar to a solar lentigo, it shows elongated, club-shaped rete ridges with marked hyperpigmentation of the basal layer. The key difference is the intensity of the pigment, which can obscure the rete ridges. The number of melanocytes is increased, but they are typically not atypical. This lack of cytologic atypia is crucial in distinguishing it from melanoma.

• Differential Diagnosis: The main concern is to distinguish it from:

  • Melanoma in situ (Lentigo Maligna): This typically has more heterogeneity in color (shades of brown, black, and tan) and more irregular, asymmetrical borders. Dermoscopy shows asymmetric pigmented follicular openings, gray dots, and an annular-granular pattern.

  • Nevus with a black network: A pigmented spindle cell nevus (Reed nevus) can also be very dark but is often more symmetric and homogeneous in its darkness and may show a more stereotypical "starburst" pattern.

• Prognosis: Excellent. It is a benign lesion with no malignant potential. It is a marker of sun exposure but not an independent risk factor for melanoma like PUVA lentigines.

• Management & Rationale:

  • Rationale: The goal is to avoid unnecessary procedures on a benign lesion while ensuring accurate diagnosis.

  • First-line: Clinical and dermoscopic recognition, followed by reassurance. Serial digital dermoscopic imaging can be used to document stability and provide further reassurance to both the clinician and the patient.

  • Treatment: Treatment is not medically necessary. If desired for cosmetic reasons, the same modalities as for solar lentigines can be used (e.g., cryotherapy, Q-switched lasers).