Dermatology MCQ - Inflammatory Dermatoses - Halo dermatitis

A 35-year-old woman notices a rapidly expanding, erythematous, and scaly ring surrounding a pre-existing, stable, and otherwise asymptomatic brown nevus on her back. The central nevus has begun to fade. A shave biopsy of the central lesion reveals a benign melanocytic nevus with no atypia. What is the most specific term for this inflammatory phenomenon?

A. Meyerson's Nevus
B. Sutton's Nevus (Halo Nevus)
C. Melanoma-Associated Halo Dermatitis
D. Halo Dermatitis
E. Irritated Nevus

Correct Answer: D. Halo Dermatitis

Explanation:

• The presentation describes Halo Dermatitis. This is a distinct entity characterized by a eczematous, inflammatory halo surrounding a central melanocytic lesion. The key differentiating feature from a classic halo nevus (Sutton's nevus) is the presence of clinical inflammation (erythema and scale) in the halo. The central nevus typically regresses due to the inflammatory attack, but the primary driver of the clinical appearance is the eczematous reaction in the surrounding skin.

• Why the other options are incorrect:

  • A. Meyerson's Nevus: This is a synonym for Halo Dermatitis. Both terms describe the same entity: an eczematous halo around a nevus. Therefore, while not incorrect, "Halo Dermatitis" is the more specific and descriptive pathological term for the inflammatory process.

  • B. Sutton's Nevus (Halo Nevus): This is the classic halo nevus, characterized by a symmetrical, uniform depigmented halo that is not erythematous or scaly. The halo is white due to complete loss of melanocytes, without the clinical signs of eczema (redness, scale). The biopsy in Sutton's nevus would show a dense lymphocytic infiltrate destroying nevus cells, but the surrounding skin appears normal, not eczematous.

  • C. Melanoma-Associated Halo Dermatitis: While a halo phenomenon can rarely occur around a melanoma, the biopsy in this case confirmed a benign nevus. Therefore, this diagnosis is incorrect.

  • E. Irritated Nevus: This term is non-specific and usually refers to a nevus that has been traumatized, leading to changes like crusting or bleeding, not a symmetrical, expanding eczematous ring.

Key Points for Exams

• Pathophysiology: Believed to be a cell-mediated immune response directed against antigens in both the nevus cells and the surrounding keratinocytes, leading to the combined features of nevus regression and eczema.

• Clinical Course: The condition is benign and self-limiting. The eczematous halo typically resolves over weeks to months with or without treatment. The central nevus often partially or completely regresses, leaving an area of post-inflammatory hypopigmentation which may later repigment.

• Key Differential Diagnosis: The most critical distinction is from a halo phenomenon around a melanoma. Any atypical features in the central lesion (irregular color, border, or asymmetry) warrant a biopsy, as was appropriately performed in this vignette.

• Management:

  1. Biopsy: If there is any doubt about the nature of the central lesion, a biopsy is mandatory to rule out melanoma.

  2. Treatment: The eczematous component can be treated with a low- to mid-potency topical corticosteroid, which will resolve the redness and scaling.

  3. Prognosis: Excellent. No specific follow-up is required for a single lesion with a histologically confirmed benign central nevus. The patient should be educated about the self-resolving nature of the condition.