Dermatology MCQ - Infiltrative and Neoplastic Disorders - LENTIGINES

A 65-year-old fair-skinned man with a significant history of chronic sun exposure presents with multiple, uniformly dark brown to black, 3-8 mm macules on his face and dorsal hands. The lesions are stable in appearance and do not change with the withdrawal of pressure from a glass slide. A biopsy of one lesion is most likely to reveal which of the following histopathological findings?

A. Atypical melanocytic hyperplasia confined to the basal layer with scattered mitotic figures.
B. Cleft-like spaces surrounding basal keratinocytes and a dense, band-like lymphocytic infiltrate.
C. Elongated and club-shaped rete ridges with an increased number of singly dispersed melanocytes.
D. Nests of melanocytes at the dermo-epidermal junction and in the papillary dermis.
E. Thickened stratum corneum with retention of nuclei and vacuolization of keratinocytes in the granular layer.

Correct Answer: C. Elongated and club-shaped rete ridges with an increased number of singly dispersed melanocytes.

Answer and Explanation

The correct answer is C. This question describes the classic presentation of a solar lentigo. The key clinical clues are the patient's age, history of chronic sun exposure, location (photo-distributed areas like face and dorsal hands), and the description of stable, uniformly pigmented macules. The negative "glass slide" test (diascopy) helps rule out vascular lesions.

Histopathologically, a solar lentigo is characterized by:

• Elongated, club-shaped (or "bud-like") rete ridges.

• An increased number of melanocytes along the basal layer, which are typically singly dispersed (not in nests).

• Hyperpigmentation of the basal keratinocytes due to increased melanin deposition.

• The dermis usually shows evidence of solar elastosis.

This combination of elongated rete ridges and an increased number of single melanocytes is the hallmark of a lentigo and distinguishes it from an ephelis (freckle), where the number of melanocytes is normal.

Why the Other Options are Incorrect:

• A. Atypical melanocytic hyperplasia confined to the basal layer with scattered mitotic figures: This describes a malignant process, specifically Lentigo Maligna (Melanoma in situ). While it arises on sun-damaged skin, it exhibits significant melanocytic atypia and pagetoid spread, which are not features of a benign solar lentigo.

• B. Cleft-like spaces surrounding basal keratinocytes and a dense, band-like lymphocytic infiltrate: This is the classic histopathology of Lichen Planus. The clefting is known as Max-Joseph spaces.

• D. Nests of melanocytes at the dermo-epidermal junction and in the papillary dermis: This describes a compound melanocytic naevus (mole). Lentigines do not form nests of melanocytes.

• E. Thickened stratum corneum with retention of nuclei and vacuolization of keratinocytes in the granular layer: This describes the histopathology of verruca vulgaris (a common wart), with its hyperkeratosis, parakeratosis, and koilocytosis.

Additional High-Yield Information for Exams:

• Differential Diagnosis: The main differential for a solar lentigo includes:

  • Ephelis (Freckle): Histology shows normal rete ridge pattern and a normal number of melanocytes (just increased melanin production).

  • Lentigo Maligna: Clinically more irregular in color and shape; histology shows atypical melanocytes.

  • Seborrhoeic Keratosis: More raised, "stuck-on" appearance, with a waxy, verrucous surface. Histology shows acanthosis and horn pseudocysts.

• Associated Conditions & Prognosis:

  • Solar lentigines are benign markers of significant cumulative sun exposure and are not pre-malignant. However, their presence indicates an increased risk for skin cancers (both melanoma and non-melanoma) due to the underlying photodamage.

  • The sudden appearance of multiple, eruptive lentigines can be a sign of the PEUTZ-JEGHERS SYNDROME (associated with gastrointestinal polyposis) or other genetic syndromes.

• Management:

  • Rationale: Treatment is primarily cosmetic, as these lesions pose no direct medical threat.

  • First-line: Cryotherapy is highly effective. Topical agents like retinoids (tretinoin) or non-thermal laser/light therapies (e.g., Q-switched lasers, IPL) are also excellent options.

  • Prevention: Strict sun protection, including daily use of broad-spectrum sunscreen, is crucial to prevent the development of new lesions and darkening of existing ones.