Review

Kaposi sarcoma is a mesenchymal tumor that primarily occurs in a mucocutaneous distribution but can potentially affect any tissue in the body. The pathogenesis of Kaposi sarcoma has been linked to human herpesvi-rus-8.¹ There are 4 clinically distinct manifestations of Kaposi sarcoma: classic Kaposi sarcoma, which occurs most commonly in elderly men of Mediterranean, Eastern European, or Jewish heritage; endemic African Kaposi sarcoma, which is seen in children and young adults in sub-Saharan Africa; iatrogenic or immunosuppression-related Kaposi sarcoma, which primarily occurs in solid organ transplant patients; and AIDS-related Kaposi sarcoma.

Arora and Goldberg² report a case of Kaposi sarcoma occurring in the small intestine without mucocutaneous involvement in a patient with no previous diagnosis or symptoms of HIV or AIDS. Upon further investigation, the patient was found to be HIV antibody–positive, with a CD4 count of less than 50 cells. This case demonstrates several key points regarding AIDS-related Kaposi sarcoma and the gastrointestinal manifestations of this disease.

At one time, Kaposi sarcoma affected up to 40% of men with AIDS in the United States. Kaposi sarcoma is approximately 20–30 times more common among homosexual or bisexual men with AIDS compared to heterosexual individuals with AIDS.³ Although the rate of AIDS-related Kaposi sarcoma has fallen dramatically since the advent of highly active antiretroviral therapy (HAART),^4,5 Kaposi sarcoma remains the most common malignancy among all patients with AIDS.⁶ Despite increased awareness and screening, improved diagnostic methods, and more advanced treatment for HIV, the diagnosis of HIV or AIDS is not always apparent when a patient presents with Kaposi sarcoma. As demonstrated by Arora and Goldberg,² an AIDS-defining malignancy such as Kaposi sarcoma can be the initial presentation of HIV infection, particularly in patients with low CD4 counts.⁷This is of particular concern in the approximately 20% of HIV-infected individuals in the United States population who are unaware of their condition.⁸

Although Kaposi sarcoma primarily manifests as a mucocutaneous disorder, visceral involvement is common and occurs in up to 25% of cases.⁹ Visceral disease tends to be more common in patients with low CD4 counts. Gastrointestinal involvement is usually asymptomatic but can present with a wide array of manifestations, including bleeding, obstruction, enteropathy, and intussusception. More subtle gastrointestinal symptoms can also occur, including abdominal pain, nausea, vomiting, diarrhea, and weight loss. These symptoms can be seen in AIDS patients for multiple other reasons; thus, the clinician must have a high degree of suspicion, particularly in the absence of coexisting cutaneous lesions. Classic (as opposed to AIDS-associated) Kaposi sarcoma commonly presents with anemia, as with the patient in this case study.¹⁰ The finding of anemia, particularly in association with microscopic blood in the stool, should prompt an evaluation for gastrointestinal Kaposi sarcoma in patients with cutaneous Kaposi sarcoma or known AIDS. The most common location in the gastrointestinal tract where Kaposi sarcoma occurs is the small intestine, followed by the colon and the stomach.¹¹ Importantly, as noted by Arora and Goldberg,² AIDS-related Kaposi sarcoma can occur in the gastrointestinal tract in the absence of cutaneous disease.^12,13

The diagnosis of Kaposi sarcoma of the gastrointestinal tract is made via endoscopy with biopsies. Endoscopically, the lesions of Kaposi sarcoma can vary from flat maculopapular lesions to large raised polypoid masses. Often, the disease will progress from patches and/or plaques to nodules, as seen in this case.¹⁴ Kaposi sarcoma is often submucosal, which can make obtaining adequate biopsy specimens challenging. Endoscopic access to Kaposi sarcoma has improved with the advent of technology that can provide direct imaging of the entire small bowel. Capsule endoscopy can visualize the entire small bowel, thus increasing the detection of Kaposi sarcoma in this part of the intestine.¹⁵ When coupled with double-balloon endoscopy or single-balloon endoscopy (as with Arora and Goldberg's case²), capsule endoscopy facilitates both endoscopic access to the small bowel as well as tissue sampling. Histologic findings of Kaposi sarcoma include spindle cells with cytologic atypia, blood vessel proliferation, extravasated red blood cells with hemosiderin deposition, and mixed plasma cell and lymphocytic infiltrate.¹⁶ Immunohistochemistry is used to identify human herpesvirus-8 and to differentiate Kaposi sarcoma from other similar-appearing gastrointestinal tumors such as high-grade sarcomas, leiomyomas, and gastrointestinal stromal tumors.

Clinical staging is based upon the extent of the tumor, the immune status of the patient, and the overall severity of the patient's systemic illness, with patients being categorized into either a good- or poor-risk group based upon each factor.¹⁷ Survival has been found to directly correlate with these factors, with increased mortality in those placed into each poor-risk category. Even patients who present with gastrointestinal Kaposi sarcoma should undergo a simple staging evaluation, including a close physical examination of the lower extremities, genitalia, face, and oral mucosa. A chest radiograph should be obtained to evaluate for pulmonary involvement, and a bronchoscopy should be used if the patient has respiratory symptoms or an abnormal chest radiograph.

The mainstay of treatment for AIDS-related Kaposi sarcoma includes HAART.^18,19 Systemic chemotherapy is used for gastrointestinal and other visceral involvement of AIDS-related Kaposi sarcoma, usually either pegylated liposomal doxorubicin or paclitaxel.^20,21 Although chemotherapy beyond HAART has become the standard of care for Kaposi sarcoma patients with gastrointestinal disease, the HIV viral load, CD4 count, and overall condition of the patient should be considered before starting systemic chemotherapy.²² The combination of HAART and systemic chemotherapy has been shown to prolong the time to treatment failure.¹⁹ Patients who are on HAART before being diagnosed with Kaposi sarcoma have a decreased mortality and the Kaposi sarcoma tends to be less aggressive. In Kaposi sarcoma patients with gastrointestinal involvement who undergo chemotherapy with doxorubicin, relapse is rare, but mortality may still be relatively high secondary to the development of other AIDS-related malignancies, particularly in patients with low CD4 counts.²³ Current 2-year survival rates for AIDS-related Kaposi sarcoma have significantly increased from 35% before 1996 to over 80% at the present time.⁷

Arora and Goldberg² present a case of AIDS-related Kaposi sarcoma involving multiple locations of the gastrointestinal tract in a previously healthy individual without cutaneous lesions. This case demonstrates that Kaposi sarcoma can be the initial presentation of HIV infection and that Kaposi sarcoma can occur anywhere throughout the gastrointestinal tract and can do so without mucocutaneous involvement.