Dermatology MCQ - Infiltrative and Neoplastic Disorders - Meyerson naevus

A 25-year-old man presents with a mole on his abdomen that has recently become itchy and scaly. On examination, a 5-mm, symmetrical, light-brown papule is noted. The lesion is surrounded by a well-defined, thin, erythematous, and scaly collarette. The central nevus itself appears benign. The patient has a history of mild atopic dermatitis. What is the most accurate statement regarding the diagnosis and management of this condition?

A. This represents an allergic contact dermatitis to the nevus cells; patch testing is required.
B. This is a Meyerson's naevus, a benign phenomenon where an eczematous reaction occurs around a pre-existing nevus; treatment with a mild topical corticosteroid is appropriate.
C. This is a sign of early malignant transformation within the nevus, warranting immediate excision.
D. This is a halo nevus in its initial inflammatory phase, and the central nevus will likely regress; observation is recommended.
E. This is a superficial fungal infection (tinea corporis) encircling a mole; treatment with a topical antifungal is indicated.

Correct Answer: B. This is a Meyerson's naevus, a benign phenomenon where an eczematous reaction occurs around a pre-existing nevus; treatment with a mild topical corticosteroid is appropriate.

Answer and Explanation

The correct answer is B. This question describes the classic presentation of a Meyerson's naevus (also known as an eczematous halo nevus). The key clinical clues are the benign-appearing central melanocytic nevus surrounded by a distinct, eczematous halo (erythema and scale). The presence of pruritus is common. This is considered a benign, inflammatory phenomenon where an eczematous dermatitis develops symmetrically around a pre-existing nevus.

Why the Other Options are Incorrect:

• A. This represents an allergic contact dermatitis...: This is incorrect. There is no specific allergen associated with nevus cells that would cause a localized allergic reaction precisely around a mole. The distribution is not typical for contact dermatitis.

• C. This is a sign of early malignant transformation...: This is incorrect and a critical distinction. While any change in a mole can be concerning, the presence of a symmetrical eczematous halo is not a feature of melanoma. Melanoma would more likely cause changes within the lesion itself (e.g., ulceration, bleeding, color change). The "collarette" of scale is highly characteristic of Meyerson's phenomenon.

• D. This is a halo nevus in its initial inflammatory phase...: This is incorrect. A halo nevus (Sutton's nevus) is characterized by a depigmented halo, not an erythematous and scaly one. The pathophysiology is different: halo nevi involve destruction of melanocytes, while Meyerson's nevi involve eczema.

• E. This is a superficial fungal infection...: This is incorrect. Tinea corporis (ringworm) typically presents as an expanding, scaly, annular plaque with a raised, leading edge and central clearing. It would not typically present as a thin, eczematous collarette symmetrically surrounding a stable nevus. A potassium hydroxide (KOH) preparation would be negative.

Additional High-Yield Information for Exams:

• Histopathology: A biopsy would show two distinct findings:

  1. A benign melanocytic nevus in the center.

  2. Features of a spongiotic dermatitis (eczema) in the epidermis surrounding and overlying the nevus, including intercellular edema (spongiosis), exocytosis of lymphocytes, and a superficial perivascular lymphocytic infiltrate.

• Differential Diagnosis: The main differential, as outlined, is to distinguish it from a halo nevus and from an eczematous change in a melanoma (which is exceedingly rare but would show atypical melanocytes). The key is the color of the halo: white in halo nevus, red and scaly in Meyerson's nevus.

• Associated Conditions & Prognosis:

  • Association with Eczema: Patients with Meyerson's phenomenon may have a personal or family history of atopic dermatitis, but it can occur in individuals without such a history.

  • Prognosis: Excellent. The eczematous reaction is self-limited and typically resolves spontaneously over weeks to months, with or without treatment. The central nevus persists unchanged after the inflammation resolves. It is a benign condition with no malignant potential.

• Management & Rationale:

  • Rationale: The goal is to relieve symptoms (pruritus) and confirm the benign nature of the lesion.

  • First-line: Application of a low- to mid-potency topical corticosteroid (e.g., hydrocortisone 2.5%, triamcinolone 0.1%) for 1-2 weeks. This will effectively treat the eczematous halo.

  • Monitoring: If the eczematous component resolves with treatment but the central nevus remains benign and unchanged, no further action is needed. If there is any doubt about the nature of the central nevus, dermatoscopic examination is crucial. Excision is reserved for cases where the diagnosis is uncertain or if the central lesion has atypical features.