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Featured Case Study
Question
A 61-year-old male presents to your clinic with a rash on his right shin. His past medical history is significant for poorly controlled HIV. His most recent CD4+ T-cell count, and viral load were 18 and 3.3 million, respectively. The patient tells you that the rash started a few months ago as small spots that seemed to get larger and spread across his shin. He has never seen a physician for the rash and has tried no previous treatments. Examination of the right lower extremity is shown in Figure 1. A punch biopsy is performed, and histopathology is shown in Figure 2.
Which of the following immunohistochemical stains would assist in achieving a definitive diagnosis?
1. CD31
2. HHV-8
3. CK20
4. Factor XIIIa
5. GLUT1
Correct Answer
Correct Answer: 2. HHV-8
Explanation
The Human herpesvirus (HHV)-8 viral stain is used to confirm the diagnosis of Kaposi’s sarcoma (KS) which is the etiology of this patient’s rash. There are 4 main types of KS: Classic, African endemic, Iatrogenic and AIDS-related.3 The patient’s history of uncontrolled HIV combined with the clinical and histopathological features presented in the question vignette should yield suspicion for KS. Histopathology of KS demonstrates an interstitial spindle cell proliferation, vascular wrapping, thin vascular spaces, extravasated RBCs, hemosiderin, and increased plasma cells.1 Application of the HHV-8 stain is especially important in the diagnosis of KS as angiosarcoma and dermatofibroma can mimic KS on histopathology.
The CD31 stain is a marker of vascular endothelial cells and is helpful in confirming the vascular origin of tumors.2 CD31 is positive in angiosarcoma. Histopathology of angiosarcoma demonstrates poorly formed vessels filled lined by large, atypical, hyperchromatic endothelial cells that protruded into the lumen. The vascular spaces are poorly formed and leaky yielding the bruise-like clinical appearance.1
The CK20 stain marks Merkel cell carcinoma in the perinuclear dot pattern. It is also helpful in determining the origin of metastatic carcinomas of unknown origin as it generally correlates with adenocarcinomas that develop in organs below the diaphragm.2 Histopathology of Merkel cell carcinoma demonstrates small blue cells with scant cytoplasm and tightly packed nuclei. Nuclear molding, apoptotic cells and mitoses can also be visualized.2
The Factor XIIIa stain highlights dermal dendritic cells and is positive in dermatofibromas and negative in dermatofibrosarcoma protuberans (DFSP).2 Histopathology of dermatofibromas demonstrate a proliferation of fibrohistiocytic cells, ringed lipidized siderophages, peripheral collagen trapping, and overlying platelike acanthosis. Another hallmark feature of dermatofibromas is their alternating areas of hypercellularity and hypocellularity. 2
Glucose transporter 1 (GLUT1) is a protein that is expressed in endothelial cells that have a blood-tissue barrier function. The GLUT1 stain is positive in infantile hemangiomas, but negative in both rapidly-involuting congenital hemangiomas (RICH) and non-involuting congenital hemangiomas (NICH).2 Histopathology of infantile hemangiomas demonstrates nonencapsulated masses of dense cords of mitotically active endothelial cells and pericytes with prominent basement membranes.4
References
1. Alikhan, Ali, and Thomas L. H Hocker. Review of Dermatology (p. 435). Elsevier, 2024.
2. Elston, Dirk M., et al. Dermatopathology (p. 133, 145, 147, 1249, 1424). Elsevier, 2019.
3. Friedman, Adam, editor, et al. Derm In-Review 2024 Study Guide (p. 310,385). SanovaWorks, 2023.
4. Nakayama, Hiroko. “Clinical and Histological Studies of the Classification and the Natural Course of the Strawberry Mark.” The Journal of Dermatology, vol. 8, no. 4, Aug. 1981, pp. 277–291, doi:10.1111/j.1346-8138.1981.tb02546.x.