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The Informed Parent

Cat Scratch Disease

by Louis P. Theriot, M.D., F.A.A.P.
Published on Jun. 17, 2002

Joey is a five-year-old boy who was brought to the office by his mom because of a large swelling in his left armpit. He brought it to her attention a few days earlier and, since he did not have a fever or any other symptoms, she elected to watch it. She actually forgot about it until he complained of a little headache the day he was brought to the office. She took his temperature; he wasn’t febrile. She then remembered the “lump” in his armpit. “Let me feel that lump you were complaining of,” she said to him. When she felt for the lump, he flinched as if it was tender. This frightened her enough to bring him right to the office.

The nurse took Joey out of the room to take his blood pressure and temperature leaving mom alone with me for a brief moment. “I wouldn’t have rushed over here without an appointment,” she said. “But I have a cousin who was just diagnosed with cancer...I think it was a lymphoma, and the only symptom that he had was a lump just like Joey’s. It scared me to death.”

Joey did not have a fever and, quite frankly, looked good. I got a detailed history that was mostly unremarkable. There was no history of fever, decreased appetite or weight loss, decreased energy or fatigue. He denied any history of trauma or infection of his left arm or hand. Mom reported that they do not have any pets, as one of my first questions was about exposure to cats or kittens.

Joey’s exam was completely normal with the exception of two findings. He had a grape-sized lymph node in his left armpit that was firm, freely moveable, neither red nor warm to touch and seemed mildly tender when touched. Joey added that it had been like that for nearly two weeks. The other finding was on the top of his left hand. A small, pinkish “pimple’-like lesion was almost completely healed. Looking at this lesion closely with a magnifying glass one could see that there was a healed linear abrasion or scratch coming from it. Joey couldn’t tell me much about this, as it never bothered him.

When pressed again about cat exposures he looked at mom and said, “We never had any cats.” She concurred. Suddenly Mom sat up and hit her forehead with her palm. “What about at Grandma’s house? She has two cats!” At least once a week they visit the grandparents where an older cat and a kitten also reside. Joey does play with them on occasion, especially since the kitten came a few months ago. Bingo! Putting this all together, Joey had a classic case of cat scratch disease.

Cat scratch disease is caused by a bacterium, Bartonella heaselae that is carried by cats and kittens. Within 3-10 days of being bitten or scratched by an infected cat, a round little pimple, usually red-brown in color, appears. This may last for days, or up to a few weeks. Yet, it usually does not cause any symptoms. This is followed by the enlarged lymph node in the area that drains the part of the body where the bite or scratch occurred. There may be one or several lymph nodes that become enlarged. If there are more than one node, they may coalesce into one large “lump”, and may actually drain. The nodes reach maximal size after 2-3 weeks. They stabilize for the next 2-3 weeks, and then resolve over the following 2-3 weeks. The entire process takes nearly 2-3 months.

Around 80% of patients with cat scratch disease will have enlarged lymph nodes. A much smaller number may complain of headache, sore throat, decreased appetite or rash. These are all self-resolving. There are much more serious “atypical” forms of cat scratch disease that include meningitis, encephalitis, ostoemyelitis (involvement of the bone), neuroretinitis (with sudden loss of visual acuity), or granulomas in the liver or spleen. Fortunately, these symptoms are quite rare and resolve completely with time.

The epidemiology of cat scratch disease is interesting. There are about 24,000 cases per year in the United States with 2,000 hospitalizations annually. Over 80% of the cases of CSD involve children 2-14 years of age with slightly more common incidence in males. There are far more cases in the latter part of the year. This probably has to do with the high mosquito population at this time of year. Cats that are infected with B. henselae have no symptoms whatsoever. However, they transmit the bacteria to humans when they bite or scratch. It turns out that the mosquitoes are instrumental in spreading the bacteria from cat-to-cat; thus, the higher incidence of infected humans in the last half of each year. This is when the mosquito population is high. Mosquitoes do not transmit the infection from cat-to-human.

All in all, cat scratch disease is a self-limiting and benign disease that should resolve completely with no residual sequelae. There are no good definitive tests to prove cat scratch disease. Thus, the diagnosis is often made with a detailed history, a thorough exam, and excluding all other possibilities. There are some studies that have shown a quicker resolution of CSD when it is treated with antibiotics. However, all cases will resolve with time if nothing is done.

Mom was relieved to learn that Joey did not have a serious illness, and Joey was even more relieved to learn that he didn’t need any blood tests. Then mom asked the inevitable question. “What should I tell my mom to do with the cats? Should she GET RID of the cats because Joey always handles them every time we go there?” I reassured her that Joey was no longer at risk for CSD, as one should get lifelong immunity after being infected. As for the cats, it depends which expert one talks to. Certainly, it is important to practice good flea control to minimize the cats becoming infected. It is probably a good idea to have the cats declawed as well. More infectious experts than not would recommend not getting rid of the cats if it would be a hard or traumatic ordeal for the family.

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