Dermatology MCQ - Infiltrative and Neoplastic Disorders - Pseudolymphoma

A 45-year-old woman presents with a solitary, violaceous, 2-cm plaque on her cheek that has been slowly enlarging over six months. There is no associated scaling or ulceration. A biopsy is performed. The histopathology reveals a dense, nodular lymphoid infiltrate in the dermis. On higher power, the infiltrate is composed of a mixture of small lymphocytes and larger cells with cleaved nuclei (centrocytes), with admixed histiocytes and eosinophils. Well-formed germinal centers are present. Which of the following is the most likely diagnosis and the most appropriate next step in management?

A. Primary cutaneous follicle center lymphoma; perform staging workup and treat with localized radiotherapy.
B. B-cell pseudolymphoma; perform a thorough workup for an underlying trigger and consider conservative excision.
C. Cutaneous T-cell lymphoma (Mycosis Fungoides); perform T-cell receptor gene rearrangement studies.
D. Chronic lymphocytic leukemia (CLL) cutis; order flow cytometry and a peripheral blood smear.
E. Lupus erythematosus tumidus; perform direct immunofluorescence and serologic testing for lupus.

Correct Answer: B. B-cell pseudolymphoma; perform a thorough workup for an underlying trigger and consider conservative excision.

Answer and Explanation

The correct answer is B. This question describes a classic presentation of cutaneous B-cell pseudolymphoma. The key clues are the solitary lesion, the mixed inflammatory infiltrate (lymphocytes, histiocytes, eosinophils), and the presence of well-formed germinal centers. This "top-heavy" nodular pattern with reactive germinal centers is a hallmark of a benign, reactive lymphoid proliferation. The management involves searching for and eliminating a causative agent (e.g., medication, tattoo, Borrelia infection, antigen injection) rather than aggressive cancer therapy.

Why the Other Options are Incorrect:

• A. Primary cutaneous follicle center lymphoma: This is the main malignant mimic. In true lymphoma, the infiltrate is typically more monomorphous (composed predominantly of centrocytes and/or centroblasts) and shows effacement of the dermal architecture. The germinal centers, if present, are often poorly formed ("atypical" or "monotonous"). A clonal population of B-cells is typically found.

• C. Cutaneous T-cell lymphoma (Mycosis Fungoides): MF is a T-cell lymphoma that classically presents with patches and plaques, often with scale. The infiltrate is primarily composed of atypical T-cells that epidermotropism (enter the epidermis), forming Pautrier microabscesses. The presence of B-cells and germinal centers argues against this.

• D. Chronic lymphocytic leukemia (CLL) cutis: This occurs in patients with known CLL. The infiltrate is monotonous and composed of small, mature-looking lymphocytes. It does not form reactive germinal centers.

• E. Lupus erythematosus tumidus: This is a form of cutaneous lupus that presents with succulent, urticarial plaques. Histology shows a perivascular and periadnexal lymphocytic infiltrate with mucin deposition in the dermis, not the dense, nodular, germinal center-forming infiltrate described.

Additional High-Yield Information for Exams:

• Histopathology (Key Features of Pseudolymphoma):

  • "Top-Heavy" Infiltrate: Primarily in the superficial and mid-dermis.

  • Mixed Cellularity: A polymorphous infiltrate including T-cells, B-cells, plasma cells, histiocytes, and eosinophils.

  • Reactive Germinal Centers: Well-defined germinal centers with tingible-body macrophages (macrophages containing apoptotic debris), polarity, and mitotic activity.

  • Preservation of Architecture: The infiltrate does not completely efface the normal dermal structures.

• Clonality Studies: A critical tool for differentiation. Pseudolymphomas typically show a polyclonal population of lymphocytes (both kappa and lambda light chains are present in B-cell lesions; a diverse T-cell receptor gene rearrangement in T-cell lesions). Lymphomas show a monoclonal population.

• Common Causes of Pseudolymphoma:

  • Medications: Anticonvulsants, antidepressants, beta-blockers, ACE inhibitors.

  • Infections: Borrelia burgdorferi (causing Borrelia lymphocytoma).

  • Antigens: Tattoo pigments, aluminum in vaccines, insect bites, acupuncture.

  • Idiopathic: No trigger found.

• Prognosis: Excellent. Pseudolymphomas are benign and often resolve completely after removal of the inciting trigger. They do not have metastatic potential.

• Management & Rationale:

  • Rationale: To rule out lymphoma and identify a treatable cause.

  • First-line:

    1. Thorough History: Review of medications, tattoos, travel, and insect bites.

    2. Serologic Testing: For Borrelia burgdorferi in endemic areas.

  • Treatment:

    • Remove the Trigger: Discontinue suspected medication.

    • For Persistent Lesions: Intralesional corticosteroids or conservative surgical excision are often curative.

    • For Refractory Cases: Topical corticosteroids, radiation therapy (which is very effective for both pseudolymphoma and true lymphoma, but used here at lower doses), or hydroxychloroquine may be used.