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Differential Diagnosis

The radiological differential diagnosis on soft tissue films (and gastrointestinal studies) includes neurofibromatosis and metastatic melanoma. Neither has characteristic angiographic findings nor can either be identified by lymphangiography. The soft tissue changes, and particularly the edema associated with diffuse osteoporosis, could be mistaken for leprosy. However, in Kaposi sarcoma there is seldom the destruction of the metatarsal heads and phalanges that occurs in leprosy. Cystic lesions occur in both diseases, but it is unusual for leprosy to involve the long bones or the carpus, as occurs in Kaposi sarcoma. Clinically, there is seldom any problem, particularly because in all races the Kaposi sarcoma is pigmented.

Maduromycosis (mycetoma) may cause clinical difficulty, because the advanced swollen leg of Kaposi sarcoma may totally disguise the underlying nodular disease. Both conditions may ulcerate and have the same woody consistency. A fungus infection tends to be unilateral and the underlying bones show marked destruction and new bone formation, neither of which is characteristic of Kaposi sarcoma. If the differential diagnosis cannot be settled clinically, angiography will undoubtedly demonstrate the underlying Kaposi nodules.

If the significance of the nodules is not recognized, the bone lesions may be mistaken for lymphosarcoma. Indeed, there is a close relationship between Kaposi sarcoma and lymphoma and the two could occur together. However, where there are bone cysts, lymphoma is unlikely. The bone lesions may closely resemble nonossifying fibromas or other fibrocystic lesions, and radiologically may be indistinguishable.

Treatment

Kaposi sarcoma is one of the rare diseases in which the diagnostic radiologist was involved in treatment. In the 1950s and 1960s the disease was effectively treated by intra-arterial chemotherapy: angiography was followed by direct intra-arterial injection of nitrogen mustard or other cytotoxic drugs. There were no immediate systemic or hematological effects. After a delay of some weeks the previously regular outline of the nodules became less well defined and shrinkage occurred. Most disappeared after 3 or 4 weeks. Repeat angiography 3 months after treatment allowed more accurate reassessment to be undertaken. A word of warning should be added: attempts were made to increase the efficiency of the intra-arterial injection by temporarily restricting the venous return. This caused severe and unexpected necrosis, and resulted in the loss of a limb. Intra-arterial therapy works if the circulation is allowed to continue without interference.

As already noted, even in HIV-negative patients, there is an association between Kaposi sarcoma and lymphoma. This is particularly true in the older patients in North America and Europe, but occurs in the tropics also. Apart from AIDS there is no clear association with any other disease except the occurrence of Kaposi sarcoma in patients on immunotherapy. Kaposi tumors have developed in patients following transplants, and have occurred at the site of surgery and subsequently become disseminated throughout the body; several such cases have occurred unexpectedly in American patients. Kaposi sarcoma has similarly developed in patients on immunosuppressive therapy for other diseases, particularly multiple myeloma and ulcerative colitis. Some authors have suggested that systemic chemotherapy (as opposed to intra-arterial) may further harm the patient's immunosuppressive mechanism, and should be used cautiously when treating Kaposi sarcoma. This is disputed by other authorities who recommend various drug combinations. One of the difficulties is the variable responses of individual patients, as well as the differences in responses in different groups. Systemic chemotherapy has produced excellent results in some series from Africa. Radiotherapy has also been recommended, both locally and using extended-field treatment. Whether radiotherapy or chemotherapy is utilized, there is a place for surgical removal of large Kaposi tumors preceding other forms of treatment. It is possible that treatment may eventually be a modification of the patient's immune state. The unexpected development of a tumor in a patient on immunosuppression should suggest the possibility of Kaposi sarcoma to the diagnostic radiologist. Conversely, it is best to avoid steroids or other immunosuppressive drugs in patients already known to have Kaposi sarcoma; there are well-documented cases in which such therapy was followed by rapid progress of the Kaposi sarcoma. It is probable that this fascinating disease will have a significant role to play in our knowledge of the immunology of malignant disease and perhaps also the etiology of some types of cancer.

Note: Unless otherwise stated, all the illustrations in this chapter were obtained in Africa prior to 1964. The arteriograms (many of which were macroradiographs) and lymphangiograms were performed in Bulawayo, Zimbabwe (then, Southern Rhodesia). Many patients received successful intra-arterial chemotherapy immediately following their arteriogram. Ultrasound, CT, and MR scanning did not exist, so these images are in Chapter 8 on AIDS.

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