This video features the first clinical-dermatopathology correlation presented by Dr. Jared Gardner, joined by dermatologist Dr. Josette McMichael, focusing on Kaposi Sarcoma (KS). Dr. McMichael outlines the clinical spectrum of this vascular neoplasm caused by HHV8, detailing its three stages (patch, plaque, tumor) and four distinct variants (Classic, African Endemic, Iatrogenic, and AIDS-related, the latter being the most aggressive and treatable with HAART).
Dr. Gardner then reviews the pathology across the stages. Early patch/plaque lesions are subtle, characterized by slit-like vascular spaces, hemorrhage, plasma cells, and the diagnostic clue of eccrine coil infiltration. Tumor stage presents as cellular nodules of bland spindle cells in fascicles, with vascular spaces appearing slit-like or forming a "sieve-like" pattern in cross-section. The critical distinction from Angiosarcoma is emphasized. Confirmation relies on immunostaining; CD34 is sensitive, while CD31 is often weak due to viral down-regulation. The essential diagnostic test is the HHV8 (LANA-1) nuclear stain, which frequently shows a characteristic punctate or stippled pattern.
Kaposi Sarcoma: Clinical and Pathologic Correlation
1:40 Clinical Definition: Kaposi Sarcoma (KS) is a vascular neoplasm caused by Human Herpes Virus 8 (HHV8). It is typically a low-grade, multi-focal, systemic disease.
3:10 Stages: KS lesions progress through three stages, which can often coexist: patch (red/violaceous macules), plaque (thickened lesions), and tumor (larger, often ulcerated nodules).
4:27 Four Clinical Variants: KS is categorized into four variants:
Classic KS (4:41): Mainly in older patients of Mediterranean/Eastern European descent; usually indolent, involving the distal lower extremities. Associated with a risk of secondary malignancy (often non-Hodgkin lymphoma).
African Endemic KS (5:52): Seen in young children and middle-aged adults in Equatorial Africa, not associated with HIV. The lymphadenopathic subgroup in children is often fatal.
Iatrogenic KS (7:00): Transplant-associated, clinically similar to classic KS. Can sometimes resolve if immunosuppression is reduced (e.g., switching to Sirolimus).
AIDS-Related KS (7:27): The most aggressive type, typically seen in patients with CD4 counts less than 500. It is often widespread (trunk, face, nose) and frequently involves visceral organs (GI tract, lungs).
12:33 Treatment (AIDS-Related): Highly Active Antiretroviral Therapy (HAART) is the first-line treatment for AIDS-associated KS. About half of patients see resolution of lesions after several months on HAART.
13:13 Pathology (Patch/Plaque Stage): Early lesions are subtle, showing increased cellularity (spindled endothelial cells mimicking fibroblasts), slit-like vascular spaces between collagen bundles, hemorrhage, and hemosiderin deposition.
14:37 Eccrine Coil Infiltration: A highly useful diagnostic clue is the infiltration of eccrine sweat gland coils by malignant spindle cells.
17:03 Promontory Sign: Refers to a small pre-existing vessel bulging into the lumen of a dilated, slit-like KS channel, creating a "vessel within a vessel" appearance.
28:08 Inflammatory Clue: The presence of numerous plasma cells in the inflammatory infiltrate is a helpful marker often seen in KS.
31:16 Pathology (Tumor Stage): Tumors are cellular nodules of plump spindle cells arranged in fascicles, often featuring an epidermal collarette.
34:44 Sieve-like Pattern: When spindle cell fascicles are cut in cross-section, the vascular spaces appear as small, round, blood-filled holes, creating a "sieve-like" pattern.
39:38 Distinction from Angiosarcoma: KS spindle cells usually have uniform and bland (monotonous) nuclei, lacking the marked pleomorphism and atypia typical of the more aggressive angiosarcoma.
46:50 Vascular Immunostains: CD34 is generally sensitive in KS. CD31 is often weak or negative because the HHV8 virus produces a protein (K5) that initiates the destruction of the CD31 molecule.
48:47 HHV8/LANA-1 Stain: The nuclear HHV8 immunostain is essential for confirmation. The staining often appears focal or "punctate/stippled" within the nucleus, and should be positive in virtually 100% of KS cases.