My second-year resident ducked his head into my office in the pediatric clinic. “Hey, Dr. Cohen,” he said, “can you come and look at a girl with a lump on her arm?”
The area on the 7-year-old girl’s upper right arm had been swelling for about a week, he said, and it was getting bigger. She’d had a slight fever about a week ago, but none since. The lump was painful and hard, and yesterday the mother had noticed some slight redness of the skin. The child had been healthy, and her immunizations were up to date. She wasn’t taking any medications, and no one at home had been ill. The resident noted that she hadn’t had any injury, such as a bite, or any exposure to animals.
We went in to see the girl. I introduced myself and crouched down beside her.
“Hi. Can I check your arm?”
She held out her arm, a wary look on her face. I began by examining her wrist and forearm, carefully feeling the tissue.
Kids’ lumps and bumps are usually benign. But sometimes they prove to be diagnostic challenges, and every once in a while they turn out to be a sign of something very serious. When a child comes in with a lump, the remote but real possibility of a tumor is always in the back of my mind. A malignant tumor often feels rock hard, as opposed to an enlarged lymph node, which is usually firm but not hard, or a cyst, which might feel soft.
“Does that hurt?” I asked. She shook her head. “Good. Can you show me where the bump is?” She pointed to the inside of her upper arm. I could see the swelling, right where the biceps muscle makes contact with the bone. My fingers slid lightly over the surface of the faintly reddened spot, then probed a little deeper. The child winced a bit, but she did not seem to be in great pain.
The swollen area was about the size of a matchbook. It felt too hard to be a benign enlarged lymph node, and it didn’t move freely under pressure as a lymph node would. Enlarged nodes tend to crop up in the armpit or around the elbow, not in the middle of the upper arm. The lump’s redness and tenderness suggested an infection, but its firmness suggested a tumor.
The resident and I decided to take blood tests and start the girl on antibiotics in case it was a local infection. We also ordered an ultrasound examination of her arm. He would see her back in the clinic in the afternoon.
The next day the radiologist informed us that the child’s lump was a lymph node, and she suspected it was enlarged due to cat scratch disease. “Cat scratch disease?” I said. “That’s a surprise. I’ll be right there.”
Once considered rare, cat scratch disease is now known to be one of the most common causes of swollen and infected lymph nodes in children. The causative bacterium, Bartonella henselae, is commonly found in cats, especially kittens. The bacteria enter the body when a child is scratched or bitten by an infected feline. Within 3 to 10 days there may be a small red bump at the site of the scratch. Over the next few days the bacteria multiply, and the child may develop a fever, headache, or other signs of mild illness. Meanwhile, the bacteria move into the intricate network of lymph vessels, a system of channels that carry fluid, pathogens, and debris out of the tissues. The lymph node becomes large and firm as bacteria multiply and attract passing immune cells that make antibodies to the pathogen. Fortunately, cat scratch disease usually subsides without treatment.
The resident reassured the child and her mother that she would get better. He sent her to the lab for a blood test to confirm the diagnosis, which would be back in a few days. After they left, we went to see the radiologist. She pointed out the distinctive appearance of an enlarged lymph node on the ultrasound image. I realized that the extreme firmness of the node was the result of the infection’s intensity and rapid progression. Still, there was one other part of the story that didn’t make sense.
“I thought she hadn’t had any exposure to animals,” I said to the resident.
“Well, that’s what she told me. Turns out she was scratched by the neighbor’s kitten a couple of weeks ago.”
“Let me guess,” I said. “She didn’t tell her mother, or us, because Mom told her not to play with the neighbor’s kitten.”
“That’s exactly right!” he said. “How did you know?”
The radiologist and I exchanged smiles, and I turned to the young resident with a grin. “You don’t have kids, do you?”
Mark Cohen is a pediatrician in Honolulu. The cases described in Vital Signs are true stories, but the authors have changed some details about the patients to protect their privacy.