Skin lesions take the form of red papules and nodules, or rounded subcutaneous masses. Histologically, there is a proliferation of capillaries lined by prominent epithelioid ECs, which exhibit nuclear atypia and mitoses (
Fig. 10.29 ). Other features include infiltrating neutrophils, nuclear debris, and purplish granular collections of the causative bacteria.
The bacteria induce host tissues to produce hypoxia-inducible factor-1α (HIF-1α), which drives VEGF production and vascular proliferation. The infections (and lesions) are cured by antibiotic treatment.
Kaposi sarcoma (KS) is a vascular neoplasm caused by Kaposi sarcoma herpesvirus (KSHV, also known as human herpesvirus-8, or HHV-8). Although it occurs in a number of contexts, it is most common in patients with AIDS; indeed, its presence is used as a criterion for the diagnosis. Four forms of KS, based on population demographics and risks, are recognized:
Classic KS is a disorder of older men of Mediterranean, Middle Eastern, or Eastern European descent (especially Ashkenazi Jews); it is uncommon in the United States. It can be associated with malignancy or altered immunity but is not associated with HIV infection. Classic KS manifests as multiple red-purple skin plaques or nodules, usually on the distal lower extremities; these progressively increase in size and number and spread proximally. Although persistent, the tumors typically are asymptomatic and remain localized to the skin and subcutaneous tissue.
Endemic African KS typically occurs in younger (under 40 years of age) HIV-seronegative individuals and can follow an indolent or aggressive course; it involves lymph nodes much more frequently than in the classic variant. In combination with AIDS-associated KS (see later), KS is now the most common tumor in central Africa. A particularly severe form, with prominent lymph node and visceral involvement, occurs in prepubertal children; the prognosis is poor, with an almost 100% mortality within 3 years.
Transplantation-associated KS occurs in solid organ transplant recipients in the setting of T-cell immunosuppression. In these patients, the risk for KS is increased 100-fold. It pursues an aggressive course and often involves lymph nodes, mucosa, and viscera; cutaneous lesions may be absent. Lesions often regress with attenuation of immunosuppression, but at the risk for organ rejection.
AIDS-associated (epidemic) KS is an AIDS-defining illness; worldwide it represents the most common HIV-related malignancy (Chapter 5). Although the incidence of KS has fallen more than 80% with the advent of antiretroviral therapy, it still occurs in HIV-infected individuals with a 1000-fold higher incidence than in the general population, and afflicts 2% to 3% of the HIV-infected
U.S. population. AIDS-associated KS often involves lymph nodes and disseminates widely to viscera early
Fig. 10.29 Bacillaryangiomatosis.(A)Characteristiccutaneouslesion.(B)Histologicfeaturesarethoseofacuteinflammationandcapillaryproliferation.Inset, Modifiedsilver(Warthin-Starry)staindemonstratesclustersoftangledbacilli(black). (A, Courtesy of Richard Johnson, MD, Beth Israel Deaconess Medical Center, Boston, Massachusetts. B and inset, courtesy of Scott Granter, MD, Brigham and Women’s Hospital, Boston, Massachusetts.) http://ebooksmedicine.net inflammatorycells,sometimescontaininghemosiderin.These in its course. Most patients eventually die of opportu lesionscanbedifficulttodistinguishfromgranulationtissue.
nistic infections rather than from KS.
•Withtime,lesionsspreadproximallyandbecomelarger,vio-