A 22-year-old heavy smoker presents with spontaneous pneumothorax. HRCT shows multiple thin-walled cysts and small stellate nodules in both upper lobes with sparing of the costophrenic angles. Immunohistochemistry on biopsy of a nodule will most likely show positivity for:
- A CD1a and S-100 ✓
- B HMB-45 and smooth muscle actin
- C CD20 and BCL-2
- D TTF-1 and cytokeratin 7
Correct answer: A. CD1a and S-100
Explanation
Pulmonary Langerhans cell histiocytosis occurs almost exclusively in young adult smokers, presenting with pneumothorax, upper-lobe stellate nodules that cavitate into thin-walled cysts, and characteristic sparing of costophrenic angles. The lesional Langerhans cells express CD1a and S-100 and show Birbeck granules on electron microscopy. HMB-45 with actin positivity defines lymphangioleiomyomatosis, which affects women and spares nothing preferentially.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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