Lymphomatoid Papulosis (LyP)

Case Overview

By Dr. Tom Davis, Sagis Diagnostics
Educational dermpath case series for dermatology residents

Patient: 20-year-old female
Lesion Location: Trunk and extremities

Clinical history: 20-year-old female with a several year history of recurrent crops of self-healing papules and nodules.

A biopsy of a recurrent papulonodular lesion was performed. Take a moment to review the histologic images below — what’s your diagnosis?

(Image 1: Low-power histologic view of papulonodular lesion)

Key Histologic Findings

On examination, several defining features stand out:

• Epidermal acanthosis
• Scattered necrotic keratinocytes in the spinous layer
• Superficial and deep perivascular infiltrate containing lymphocytes, extravasated erythrocytes, and, at times, neutrophils and eosinophils
• Numerous large, atypical CD30+ mononuclear cells with pleomorphic hyperchromatic nuclei and abundant cytoplasm

(Image 2: Medium power showing perivascular and interstitial infiltrate of mononuclear cells)

(Image 3 & 4: High power showing large, atypical mononuclear cells with pleomorphic nuclei.)

(Image 5: Immunohistochemical stain demonstrating CD30 expression of atypical mononuclear cells)

Differential Diagnosis: Three Common Mimickers

When evaluating a recurrent papulonodular eruption with atypical lymphoid infiltrate like this, several differentials come to mind. Let’s walk through the three most likely contenders and highlight what sets them apart.

1️⃣ Mucha-Habermann Disease (PLEVA)

Etiology: Idiopathic; believed to represent a clonal T-cell disorder or hypersensitivity reaction, possibly triggered by infection

Histology:

• Superficial and deep lymphocytic infiltrate
• Epidermal spongiosis and necrotic keratinocytes
• Interface dermatitis pattern with vacuolar change
• Extravasated erythrocytes
• Lacks large atypical mononuclear cells

Key Distinction: PLEVA may bear striking histologic similarity to LyP at low power, sharing a superficial and deep lymphocytic infiltrate and necrotic keratinocytes. However, PLEVA lacks the large atypical CD30+ mononuclear cells that characterize LyP. Careful high-power evaluation is essential for this distinction.

(Image 6: PLEVA histology — interface dermatitis without atypical mononuclear cells)

2️⃣ Insect Bite Reaction

Etiology: Arthropod hypersensitivity — IgE- and cell-mediated immune response to salivary antigens

Histology:

• Mixed cell infiltrate with prominent eosinophils
• Superficial and deep perivascular infiltrate
• Spongiosis and epidermal changes
• Dermal edema
• Devoid of large atypical mononuclear cells

Key Distinction: Insect bite reactions can mimic LyP at low power due to a brisk mixed perivascular infiltrate. The key distinguishing feature is the presence of numerous eosinophils and the conspicuous absence of large atypical CD30+ mononuclear cells. Clinically, insect bites are episodic and site-specific, lacking the chronic waxing-and-waning pattern of LyP.

3️⃣ Primary Cutaneous Anaplastic Large Cell Lymphoma (PC-ALCL)

Etiology: CD30+ T-cell lymphoproliferative disorder; shares a disease spectrum with LyP

Histology:

• Diffuse, cohesive sheets of large CD30+ cells comprising >75% of the infiltrate
• Large pleomorphic or anaplastic cells with prominent nucleoli
• Sparse inflammatory background — in contrast to the rich mixed infiltrate of LyP
• Typically presents as a solitary or localized persistent nodule or tumor

Key Distinction: PC-ALCL is the most diagnostically challenging mimicker of LyP because both conditions are CD30+ lymphoproliferative disorders existing on the same disease spectrum. Histologically, PC-ALCL shows diffuse cohesive sheets of large CD30+ cells comprising more than 75% of the infiltrate, whereas in LyP the atypical cells are scattered within a rich inflammatory background. The most critical distinguishing feature is clinical: PC-ALCL presents with persistent solitary or localized nodules, while LyP manifests as chronic, recurrent papulonodular lesions that spontaneously resolve.

The Final Diagnosis: Lymphomatoid Papulosis (LyP)

The combination of large atypical CD30+ mononuclear cells with pleomorphic hyperchromatic nuclei, set within a mixed inflammatory perivascular infiltrate, coupled with a clinical history of recurrent self-healing papulonodular lesions that wax and wane over months to years, is diagnostic of Lymphomatoid Papulosis. Critically, this diagnosis cannot be made on pathology alone — clinicopathologic correlation is paramount.

Key Takeaways for Residents:

• LyP is a benign but chronic condition — individual lesions spontaneously resolve, but new crops recur over months to years.
• CD30 expression alone does not make the diagnosis; the proportion of CD30+ cells and clinical context are both essential.
• PLEVA may closely resemble LyP at low power — high-power evaluation for large atypical mononuclear cells is critical.
• The distinction between LyP and PC-ALCL is primarily clinical: LyP resolves spontaneously; PC-ALCL persists.
• Close clinical follow-up is mandatory: patients with LyP carry a 4–25% risk of developing associated lymphomas, most commonly mycosis fungoides, followed by anaplastic large cell lymphoma and Hodgkin lymphoma.

📚 Quick Summary

💬 Final Thought

The CD30+ lymphoproliferative disorders exist on a spectrum with considerable microscopic and immunohistochemical overlap.  Definitive and correct diagnosis is only possible when the microscopic findings are correlated with patient history and clinical findings.

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