This video provides a detailed dermatopathology review of Langerhans cell histiocytosis (LCH) of the skin, guided by the analysis of a biopsy slide. Dr. Gardner and a colleague discuss the diagnostic process, starting from a low-power view of a dense inflammatory infiltrate and considering differential diagnoses such as atypical lymphoid infiltrates or exuberant bug bite reactions. The discussion then moves to high-power examination, highlighting the characteristic reniform, coffee bean-shaped, or grooved nuclei of Langerhans cells, their tendency to pack the papillary dermis and scatter into the epidermis, which distinguishes them from other conditions like mastocytosis. Key immunohistochemical markers like S100, CD1A, and Langerin (CD207) are emphasized for confirmation. The video also clarifies the distinction between LCH and Rosai-Dorfman disease, despite both being S100 positive, based on significant morphological and locational differences. Advanced diagnostic aids like Cyclin D1 positivity and BRAF V600E mutations are presented as useful tools for ambiguous cases, alongside a brief mention of LCH's varied clinical presentations.
Langerhans Cell Histiocytosis of Skin (LCH): Pathology and Diagnosis
0:14 Initial Biopsy Assessment: The video begins with the examination of a shaved biopsy exhibiting significant inflammation, prompting a differential diagnosis including atypical lymphoid infiltrates or a very dense, blue process, potentially even an exuberant bug bite reaction.
0:44 Characteristic Cell Morphology: Upon closer inspection, the presence of various cell types, including eosinophils and lymphocytes, is noted, alongside larger cells with distinct reniform, coffee bean-like, or grooved nuclei, which are highly suggestive of Langerhans cells.
1:04 Immunostains for Diagnosis: Based on the cell morphology, Langerhans cell histiocytosis is suspected, and stains such as S100 and CD1A are recommended for definitive diagnosis.
1:38 Papillary Dermis Infiltrate: A key feature of LCH is the infiltration of Langerhans cells densely packing the papillary dermis, a characteristic also seen in mastocytosis.
2:15 Epidermal Scatter: Unlike mastocytosis, Langerhans cells in LCH typically "trickle up" and scatter into the epidermis, reflecting their normal epidermal residence and ability to cross the dermal-epidermal junction.
2:41 Cytological Distinctions: While both Langerhans cells and mast cells have oval nuclei and pale cytoplasm, Langerhans cells possess the unique bean-shaped, reniform, or grooved nuclei, whereas mast cells have oval nuclei and granules (though often hard to see). Eosinophils are frequently abundant in LCH.
3:12 Differentiating from Rosai-Dorfman Disease: Although both LCH and Rosai-Dorfman disease are S100 positive histiocytic processes, they are morphologically and clinically distinct, usually precluding confusion in differential diagnosis.
4:05 Specific LCH Markers: CD1A and Langerin (CD207) are specific markers for Langerhans cells; Langerin is a surrogate marker for Birbeck granules, which are typically seen on electron microscopy.
4:34 Variable Clinical Presentations: LCH can manifest differently, ranging from skin-only involvement to more aggressive systemic disease affecting lungs, bone, or skull base, necessitating a thorough clinical workup.
5:22 Cyclin D1 and BRAF Mutations: In ambiguous cases, Cyclin D1 positivity via immunohistochemistry (as reactive Langerhans cells are negative) and the detection of activating BRAF V600E mutations can aid in confirming the diagnosis of LCH, though not all cases have the mutation.
6:47 Cytological Examples: Additional images are provided to illustrate extensive upward scatter of Langerhans cells, which, if S100 positive, might mimic melanoma but would be negative for SOX10, and clear examples of the characteristic bean-shaped, kidney-shaped, or grooved nuclei.