Cat Scratch in AIDS Cases May Be Misdiagnosed

Skin lesions caused by cat scratches might be misdiagnosed as a form of cancer in AIDS patients unless a detailed laboratory analysis is performed, researchers have found.

Even to the trained eye of an expert in skin diseases, cat scratch disease in AIDS patients can look just like Kaposi’s sarcoma, a type of cancer rarely seen in the general population but often found in people with AIDS.

Misdiagnosis might mean unnecessary, expensive and debilitating cancer therapy for patients already weakened by acquired immune deficiency syndrome.

Doctors reporting in a recent issue of the British medical journal Lancet say seven AIDS patients in San Francisco and New York were mistakenly diagnosed with Kaposi’s because the scratches created lesions involving small blood vessels, mimicking the malignancy’s appearance.

“Cat scratch disease does not look like this in healthy people,” explained Dr. Philip LeBoit, an assistant clinical professor of pathology and dermatology at UC San Francisco.

“This seems to fit into that classification of conditions known as pseudomalignancies, at least as far as AIDS is concerned. Pseudomalignancies are not cancer but look like cancer,” he said.

LeBoit led a laboratory analysis that revealed clusters of bacteria identical to those associated with cat scratch disease in tissue samples taken from each of the patients. The unusual bacteria cause lymph node swelling in healthy people and can be successfully treated with antibiotics.

But in people afflicted with AIDS, whose immune systems are impaired by the AIDS virus, the scratches can lead to further complications, LeBoit said.

Two deaths of AIDS patients associated with cat scratch disease have been recorded in medical literature, LeBoit noted. He added that even in people with AIDS, cat scratch disease can be easily cured with proper treatment.

He believes that some of the skin lesions in AIDS patients elsewhere in the country--especially outside of the big cities where AIDS is prevalent--may have been misdiagnosed as Kaposi’s.

“There is a subset of AIDS patients, probably a small minority, whose lesions mimic Kaposi’s sarcoma clinically and under the microscope,” he said.

The studies also reveal that the bacteria that cause cat scratch disease are so elusive that rare staining techniques or a powerful electron microscope may have to be used to find them. In other cases, several skin samples may have to be taken from patients before a definitive diagnosis can be made.

The kinship between cat scratch disease and Kaposi’s sarcoma is not new and apparently the two share an evolving relationship in the pages of medical literature, now dating back about four years.

Dr. Mark Stoler of the University of Rochester in New York in 1984 was among the first to recognize that an AIDS patient with skin lesions involving the small blood vessels probably was not a victim of Kaposi’s sarcoma.

Splotches on Skin

Stoler, a co-author with LeBoit on the Lancet paper, suggested at the time that a laboratory analysis might reveal something quite unrelated to the cancer, which is characterized by purple or dark-brown splotches on the skin.

“The two even look alike under the microscope,” Stoler said, referring to an examination of affected tissue under the light microscope.

In some cases, these subtle differences can only be resolved with a more thorough examination under the more powerful electron microscope.

Stoler said he knows of no AIDS patients who unnecessarily underwent cancer therapy but added, “It’s not impossible, since (the relationship between the two diseases) was only recently described.”