Cutaneous Pseudolymphoma
Cutaneous pseudolymphoma (CPL) is a clinical and histopathologic term for a group of benign, reactive proliferations of T or B lymphocytes in the skin. Their clinical appearance, microscopic pattern and sometimes even immunohistochemistry can closely resemble cutaneous lymphoma. Unlike true lymphoma, which is a malignant monoclonal neoplasm, pseudolymphoma is at heart a benign polyclonal immune reaction to an external or internal trigger, and it can resolve completely once the cause is removed.
The biggest challenge for dermatologists and pathologists is to reliably distinguish pseudolymphoma from early true T- or B-cell lymphoma, so that overdiagnosis does not lead to unnecessary, toxic chemotherapy or radiotherapy.
At Haute-Derma, we take a comprehensive approach: a detailed allergy and exposure history, high-magnification dermoscopy, excisional skin biopsy, a full immunohistochemistry (IHC) panel and molecular clonality testing (TCR/BCR gene rearrangement). This lets us confirm the diagnosis and choose the best conservative treatment.
Clinical and Pathologic Features
Causes and Clinical Types
Cutaneous pseudolymphoma results from excessive recruitment and proliferation of reactive immune cells. Depending on the predominant cell type, CPL falls into two main groups:
- Cutaneous B-Cell Pseudolymphoma (Lymphocytoma Cutis):
- Common causes: insect bites and stings, tattoos (especially red ink containing mercury or cadmium), physical trauma, infection with Borrelia burgdorferi (Lyme disease), medications (such as phenytoin, carbamazepine and ACE inhibitors), or vaccination.
- Appearance: a solitary, raised, smooth, well-defined red-purple nodule or plaque, usually on the face, earlobe, areola or limbs.
- Cutaneous T-Cell Pseudolymphoma (Actinic Reticuloid / Drug-Induced CPL):
- Common causes: chronic photosensitivity (actinic reticuloid), persistent allergic contact reactions (for example to nickel or cobalt), and reactions to systemic medications.
- Appearance: infiltrated, scaly, intensely itchy red plaques on sun-exposed skin, or widespread lesions resembling chronic eczema.
Histopathology
- "Top-heavy" vs. "bottom-heavy" pattern: B-cell pseudolymphoma is usually wedge-shaped or concentrated in the superficial and mid dermis ("top-heavy"), with a normal overlying epidermis separated by a clear band (Grenz zone).
- Reactive lymphoid follicles: well-formed germinal centers containing a mix of small lymphocytes, large lymphoid cells (centroblasts/centrocytes), tingible body macrophages and normal mitoses.
- Polymorphous infiltrate: alongside T and B lymphocytes there are usually plenty of eosinophils, plasma cells and foamy cells.
Differential Diagnosis and Immunohistochemistry (IHC)
| Feature | Cutaneous pseudolymphoma | True cutaneous lymphoma |
|---|---|---|
| Clonality | Polyclonal: B cells express both kappa and lambda light chains (normal kappa:lambda ratio of 1:1 to 3:1). No monoclonal TCR/BCR rearrangement. | Monoclonal: restricted expression of kappa or lambda only. PCR shows a sharp monoclonal TCR/BCR rearrangement band. |
| Follicle pattern | Clear germinal centers with tingible body macrophages; high physiologic mitotic rate within germinal centers. | Normal germinal center architecture is lost; diffuse sheets of uniform atypical cells or pseudofollicles. |
| IHC (T-cell CPL vs. MF) | Full expression of T-cell surface markers: CD3+, CD4+, CD8+, CD7+. | Loss of pan-T-cell markers (e.g., CD7− or CD2−); atypical cells with convoluted, cerebriform nuclei. |
| IHC (B-cell CPL vs. CBCL) | CD20+ in follicles; BCL-2 negative (or weakly positive) in germinal centers; very high Ki-67 confined to germinal centers. | Strong, diffuse BCL-2 positivity within germinal centers (a key criterion for PCFCL); haphazard Ki-67 distribution. |
Our Approach to Treating Cutaneous Pseudolymphoma
Haute-Derma manages pseudolymphoma on the principles of conservative, cautious medicine:
- Find and Remove External Triggers First: we thoroughly review medications, insect bites, tattoos, contact allergies and infections (Borrelia) before deciding on medical treatment.
- Avoid Over-Treatment: we do not rush into systemic chemotherapy, wide-field radiotherapy or heavy immunosuppression before polyclonality has been confirmed.
- Stepwise Approach: local treatments (topical or intralesional corticosteroids, tacrolimus) or treating the root cause come first, before minor surgery is considered.
How We Diagnose Pseudolymphoma at Haute-Derma
To rule out true lymphoma and confirm a benign reactive process, Haute-Derma follows a four-step workup:
- Clinical Examination, Dermoscopy and Exposure History: we assess the red-purple nodule or plaque and look on dermoscopy for branching vessels, raised white lines and orange-pink areas. We review any history of tattoos, insect bites or oral medications.
- Excisional or Deep Punch Biopsy: a deep sample through the dermis into the subcutaneous fat lets us assess the full "top-heavy" architecture and the presence of germinal centers.
- Differential IHC Panel: staining for CD3, CD20, BCL-2, CD7, CD21/CD23 (follicular dendritic cells), Ki-67 and kappa/lambda light chains.
- Molecular Confirmation (TCR/BCR Gene Rearrangement): PCR analysis of T- and B-cell receptor gene rearrangement. A polyclonal result is the gold-standard evidence of benign pseudolymphoma.
Specialized Treatment at Haute-Derma
Treatment of pseudolymphoma at Haute-Derma aims to clear the lesion and restore the skin's appearance:
- Treating the Root Cause:
- Stopping suspected culprit medications (after consulting the relevant specialist).
- Systemic antibiotics (such as doxycycline) if Borrelia burgdorferi infection is suspected or serology is positive.
- Topical and Intralesional Therapies:
- Intralesional triamcinolone acetonide (TAC): injected directly into the nodule, it quickly flattens solitary B-cell CPL lesions.
- Potent topical corticosteroids / topical calcineurin inhibitors: clobetasol propionate or 0.1% tacrolimus for superficial T-cell CPL plaques.
- Phototherapy and Lasers:
- Narrowband UVB (NB-UVB) for photosensitive T-cell pseudolymphoma (actinic reticuloid).
- Ultrapulse CO2 laser or pulsed dye laser (PDL) to treat residual redness and raised texture once the inflammation has subsided.
- Cosmetic Surgical Excision: for small, solitary lymphocytoma cutis nodules on the face or earlobe that do not respond to corticosteroid injections, or that are caused by tattoo ink allergy and will not resolve.
