Rosai-Dorfman disease hallmark microscopic features
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Rosai-Dorfman Disease (RDD) - Hallmark Microscopic Features
1. The Defining Hallmark: Emperipolesis
The absolute hallmark of RDD is emperipolesis - the presence of intact, viable hematopoietic cells within the cytoplasm of large histiocytes. The engulfed cells include:
- Lymphocytes (most common)
- Plasma cells
- Erythrocytes
- Neutrophils
This is distinct from phagocytosis - in emperipolesis the engulfed cells remain intact and viable (not degraded), often appearing to "swim" within the large pale cytoplasm of the host histiocyte.
Fitzpatrick's Dermatology describes it precisely: "different types of bone marrow cells, such as lymphocytes or neutrophils, are found in the cytoplasm of histiocytes."
2. The RDD Histiocytes Themselves
The large histiocytes that characterize RDD have:
- Abundant pale/clear cytoplasm (sometimes described as foamy or vacuolated)
- Large vesicular nuclei with prominent nucleoli
- Hypochromatic nuclei (Goldman-Cecil)
- They proliferate within lymph node sinuses (hence "sinus histiocytosis")
3. Lymph Node Architecture (Nodal Disease)
- Dilated sinuses packed with the large histiocytes showing emperipolesis
- Cortical regions contain abundant plasma cells (often polyclonal) and activated B lymphocytes
- Background inflammatory infiltrate of mature lymphocytes and plasma cells
4. Immunohistochemistry Profile
| Marker | Result | Significance |
|---|---|---|
| S100 | Positive | Key diagnostic marker; also used as serum marker |
| CD68 | Positive | Macrophage lineage |
| CD163 | Positive | Macrophage/monocyte marker |
| CD14 | Positive | Macrophage marker |
| HLA-DR | Positive | |
| α₁-antitrypsin | Positive | |
| α₁-antichymotrypsin | Positive | |
| Fascin | Positive | |
| HAM-56 | Positive | Human alveolar macrophage 56 |
| Stabilin-1 | Positive | |
| Cyclin D1 + pERK | Positive | MAPK pathway activation |
| OCT2 (nuclear) | Positive | Recent finding (51/51 cases) |
| CD1a | Negative | Key distinction from LCH |
| CD207 (Langerin) | Negative | Key distinction from LCH |
The S100+/CD1a- combination is the cardinal IHC signature.
5. Photomicrographs from Fitzpatrick's Dermatology
Panel A - S100 immunostain showing histiocyte positivity:
Panel B - Stabilin-1 staining:
Figures 117-13A and 117-13B from Fitzpatrick's Dermatology - histiocytes are positive for both S100B and stabilin-1
6. Cutaneous RDD (Extranodal)
In skin biopsies, the same features apply but the infiltrate is typically in the dermis and subcutis:
- Dense infiltrate of large pale histiocytes with emperipolesis
- Abundant polyclonal plasma cells
- IgG4-positive plasma cells may be present within the infiltrate (though RDD ≠ IgG4-related disease)
7. Key Differential Diagnosis by Microscopy
| Feature | RDD | Langerhans Cell Histiocytosis | Juvenile Xanthogranuloma |
|---|---|---|---|
| Emperipolesis | Yes (hallmark) | Rare | Rare (occasionally) |
| S100 | + | + | Can be + (large macrophages) |
| CD1a | Negative | Positive | Negative |
| Langerin (CD207) | Negative | Positive | Negative |
| Birbeck granules (EM) | Absent | Present | Absent |
| Touton giant cells | Absent | Absent | Present |
RDD is distinguished from LCH by the absence of CD1a/CD207 staining.
Summary: The microscopic signature of Rosai-Dorfman disease is large, pale S100+/CD1a- histiocytes showing emperipolesis (intact lymphocytes, plasma cells, and erythrocytes within their cytoplasm), set against a background rich in plasma cells, filling lymph node sinuses or dermal/subcutaneous tissue.
Sources:
- Fitzpatrick's Dermatology, Vol. 1-2, p. 2060 (Histopathologic Findings)
- Dermatology 2-Volume Set 5e (Dermatology 5e), "R" Group: Rosai-Dorfman Disease, Pathology section
- Goldman-Cecil Medicine, Pathobiology of Rosai-Dorfman-Destombes
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