Dermatology MCQ - Inflammatory Dermatoses - Lichen simplex chronicus

A 45-year-old woman presents with a circumscribed, lichenified, hyperpigmented plaque on the posterior aspect of her neck. She reports that the area is intensely pruritic and that she frequently rubs and scratches it throughout the day, which provides transient relief. The surrounding skin is normal. What is the most likely diagnosis?

A. Psoriasis
B. Plaque Parapsoriasis
C. Lichen Simplex Chronicus
D. Tinea Corporis
E. Mycosis Fungoides

Correct Answer: C. Lichen Simplex Chronicus

Explanation:

• The presentation is classic for Lichen Simplex Chronicus (LSC). This is a skin disorder characterized by lichenification (thickening of the skin with accentuated skin markings) resulting from repeated scratching or rubbing in response to chronic pruritus. The key diagnostic clues are the well-circumscribed plaque, the history of intense pruritus leading to a scratch-itch cycle, and the common location (posterior neck is a classic site). The primary pathology is the behavioral component of chronic scratching.

• Why the other options are incorrect:

  • A. Psoriasis: Psoriatic plaques are typically well-demarcated with a thick, silvery scale. While pruritus can occur, the primary driver is not a behavioral scratch-itch cycle. Psoriasis also commonly presents in other classic locations (scalp, elbows, knees) and may show other signs like nail pitting or Auspitz sign.

  • B. Plaque Parapsoriasis: This presents as chronic, asymptomatic or mildly pruritic, scaly patches that are not typically associated with vigorous scratching or marked lichenification.

  • D. Tinea Corporis: This fungal infection presents as an annular, expanding plaque with a raised, scaly, and often vesicular border. It would not be expected to remain as a single, stable, lichenified plaque for a prolonged period without spreading in an annular pattern.

  • E. Mycosis Fungoides: Early patches of this cutaneous T-cell lymphoma can be eczematous or psoriasiform. However, the intense, localized pruritus and the clear history of a self-induced scratch-itch cycle causing lichenification are highly characteristic of LSC. A biopsy may be needed to definitively rule out MF in persistent cases, but the clinical history strongly favors LSC.

Key Points for Exams

• Pathophysiology: A "scratch-itch cycle" where initial pruritus (which may have a primary cause or be idiopathic) leads to scratching, which causes skin damage and inflammation, which in turn releases more pruritogenic mediators, perpetuating the cycle.

• Common Locations: Posterior neck, scalp, extensor forearms, wrists, ankles, vulva, and scrotum.

• Underlying Causes: It is crucial to determine if the LSC is primary (neurodermatitis) with no underlying cause, or secondary to an underlying pruritic condition that has been scratched, such as atopic dermatitis, contact dermatitis, or lichen planus.

• Prognosis: The condition is chronic and tends to recur if the scratching behavior is not interrupted. Prognosis is good with strict adherence to treatment aimed at breaking the cycle.

• Management: The cornerstone of treatment is breaking the scratch-itch cycle.

  1. Topical High-Potency Corticosteroids: First-line therapy to rapidly reduce inflammation and pruritus. Occlusive dressings can be used over the steroid to enhance penetration and provide a physical barrier against scratching.

  2. Intralesional Corticosteroids: For very thick, recalcitrant plaques.

  3. Behavioral Modification: The patient must be made aware of the cycle. Conscious avoidance of scratching is critical.

  4. Adjunctive Therapies: Oral antihistamines (especially sedating ones at night) to reduce pruritus. In refractory cases, phototherapy or neuromodulators like gabapentin or pregabalin may be considered.