Dermatology MCQ - Infiltrative and Neoplastic Disorders - Lymphocytoma cutis

A 35-year-old woman presents with a solitary, violaceous, firm nodule on her earlobe that has been present for 4 months. She recalls a tick bite in the same area approximately one week before the nodule appeared. A biopsy reveals a dense, "top-heavy," nodular lymphoid infiltrate in the dermis composed of a mixture of small lymphocytes and larger cells with cleaved nuclei (centrocytes). Well-formed germinal centers with tangible-body macrophages are present. Special stains for microorganisms are negative. What is the most likely diagnosis and the implicated causative agent?

A. Primary cutaneous marginal zone lymphoma; no specific infectious agent is typically implicated.
B. Lymphocytoma cutis; most commonly associated with Borrelia burgdorferi infection.
C. Cutaneous follicle center lymphoma; associated with Helicobacter pylori infection.
D. B-cell chronic lymphocytic leukemia cutis; caused by clonal expansion of CD5+ B-cells.
E. Cutaneous sarcoidosis; a non-caseating granulomatous disease of unknown cause.

Correct Answer: B. Lymphocytoma cutis; most commonly associated with Borrelia burgdorferi infection.

Answer and Explanation

The correct answer is B. This question describes a classic presentation of lymphocytoma cutis, specifically the Borrelial type. The key clues are the history of a preceding tick bite, the location (earlobe and nipple are classic sites for Borrelial lymphocytoma), and the benign, reactive histology showing a mixed infiltrate with well-formed, reactive germinal centers. Borrelia burgdorferi is the most well-defined infectious cause of this B-cell pseudolymphoma, especially in endemic areas.

Why the Other Options are Incorrect:

• A. Primary cutaneous marginal zone lymphoma: This is a true low-grade B-cell lymphoma. It can appear very similar clinically and histologically. However, the history of a direct temporal relationship with a tick bite is highly suggestive of a reactive process. Histologically, lymphomas may show a more monomorphous population of cells and less well-defined germinal centers.

• C. Cutaneous follicle center lymphoma: This is a B-cell lymphoma derived from germinal center cells. It typically presents with plaques or tumors on the head, neck, or trunk. It is not associated with H. pylori; that association is with gastric MALT lymphoma.

• D. B-cell chronic lymphocytic leukemia cutis: This presents in patients with known CLL. The infiltrate is monotonous and composed of small, round, mature-looking lymphocytes (not a mixed infiltrate with germinal centers).

• E. Cutaneous sarcoidosis: This is characterized by non-caseating granulomas on histology, not a dense lymphoid infiltrate with germinal centers.

Additional High-Yield Information for Exams:

• Histopathology: The hallmark is a benign, reactive-looking pattern.

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

  • Reactive Germinal Centers: Well-defined germinal centers containing a mix of centrocytes and centroblasts, with tangible-body macrophages (evidence of apoptosis, a sign of high cell turnover).

  • Mixed Cell Population: The infiltrate between germinal centers is polymorphous, containing T-cells, plasma cells, and histiocytes.

  • Lack of Monoclonality: Immunohistochemistry or gene rearrangement studies typically show a polyclonal population of B-cells (both kappa and lambda light chains are present).

• Common Causes:

  • Infections: Borrelia burgdorferi (most common identified cause), Borrelia afzelii (in Europe), Staphylococcus aureus.

  • Antigens: Tattoo pigments, insect bites, vaccinations, metal (e.g., gold, aluminum).

  • Medications: Anticonvulsants, antidepressants, beta-blockers.

  • Idiopathic: No trigger is found in many cases.

• Differential Diagnosis: The most important distinction is from a low-grade B-cell lymphoma, such as primary cutaneous marginal zone lymphoma or follicle center lymphoma. Clinical history (e.g., tick bite) and histology with well-formed germinal centers favor pseudolymphoma, but clonality studies are often necessary for a definitive diagnosis.

• Prognosis: Excellent. It is a benign, reactive condition. Lesions often resolve spontaneously or after treatment of the underlying cause (e.g., antibiotics for Borrelia). They do not have metastatic potential.

• Management & Rationale:

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

  • First-line:

    1. Thorough History: Inquire about tick bites, medications, tattoos, etc.

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

  • Treatment:

    • Specific: If Borrelia is suspected or confirmed, a course of oral antibiotics (e.g., doxycycline, amoxicillin) is first-line treatment.

    • Non-specific: Intralesional corticosteroid injections are highly effective.

    • Other Options: Surgical excision is both diagnostic and curative for a solitary lesion. Topical corticosteroids, cryotherapy, or hydroxychloroquine can also be used.