A 3-year-old boy presents with a painless lytic lesion of the skull with soft tissue swelling, polyuria, and polydipsia. Biopsy shows sheets of cells with grooved coffee bean nuclei admixed with eosinophils. Which marker confirms the diagnosis?
- A CD1a positivity on CD45 positive cells ✓
- B CD20 positivity with surface immunoglobulin
- C CD99 membranous positivity
- D Myeloperoxidase positivity
Correct answer: A. CD1a positivity on CD45 positive cells
Explanation
Langerhans cell histiocytosis is a clonal proliferation of myeloid derived dendritic cells. The Birbeck granule bearing Langerhans cells express CD1a and langerin (CD207), and electron microscopy shows tennis racket shaped Birbeck granules. Skull lytic lesions plus diabetes insipidus from posterior pituitary infiltration are classic multisystem features. CD99 marks Ewing sarcoma, CD20 marks B-cell lymphomas, and myeloperoxidase marks myeloid lineage, none of which fit this histology.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.