A previously healthy 10-year-old boy presented to the clinic complaining of a painful mass high on his left anterior thigh for the past two days. The lump was tender, red and prohibited his gait. He also reported a low-grade fever. Two days earlier, he had scratched his left leg at the shin, but the abrasions had healed well. Otherwise, he had no recent illnesses, trauma, travel, exposure to tuberculosis or other contagious diseases, sweats, chills or weight loss and his appetite was good. His past medical history was unremarkable. He was on no medications. His family had no pets, and while a downstairs neighbor raised kittens, he reportedly never had contact with them.
On exam, he had a temperature of 98.9° F, with a pulse of 90 beats/min, blood pressure of 93/53 mm Hg and respirations of 18 breaths/min. He had a swollen, tender, warm, red mass measuring 6x7 cm in the left femoral area. There was no fluctuance or streaking. The pain at the mass site inhibited external rotation, internal rotation and abduction of the hip. There was a 1-cm healing abrasion on his anterior left calf. His physical exam was otherwise unremarkable.
On admission to the hospital, his WBC count was 4,800/mm3 with 44% neutrophils, 44% lymphocytes, 11% monocytes and 1% eosinophils, hematocrit was 33.2% and platelets of 199,000/mm3. Blood was drawn for culture. He was started on intravenous oxacillin and clindamycin for coverage of the most common causes of bacterial adenitis in children, Staphylococcus aureus and group A streptococcus.
On the day of admission, his temperature peaked at 100.5° F. After three days of therapy, the mass had only minimally decreased. The blood culture was negative. Concerned about an abscess, the inpatient team obtained an ultrasound which revealed two enlarged and tender femoral lymph nodes, each 2x3 cm, without evidence of a fluid collection. Because of his failure to respond to antibiotic coverage for traditional causes of adenitis, sera were sent for antibodies to Bartonella henselae and he was treated with a five-day course of azithromycin (Zithromax, Pfizer) for presumptive cat scratch disease. He was discharged on hospital day five with the mass still 4x6 cm.
One week later, he returned to the clinic. He reported less pain, but the mass was still 4x5 cm. Two days later, a PPD test was negative, but IgM and IgG antibody titers to B. henselae were positive by the immune fluorescence antibody (IFA) test, strongly suggestive of cat scratch disease. He completed another five-day course of azithromycin. When seen about four weeks after his original presentation, the mass had completely resolved.
B. henselae, the likely causative agent of cat scratch disease, is a fastidious, slow-growing, gram-negative bacteria. The most frequent manifestation of cat scratch disease is tender regional lymphadenopathy or lymphadenitis in otherwise healthy young people. Adenitis is most commonly located in the axillary and cervical area, yet was seen in our case in the inguinal area (depending on where the initial inoculum breaks the skin).
Although more than 90% of patients have a history of recent contact with cats (most often a definite cat scratch or bite, often by kittens), other animals and inanimate objects have been implicated in transmission as well. There is no evidence of person-to-person transmission.
Chronicity and a lack of fever, elevated WBC count or spreading erythema should prompt evaluation for atypical causes of adenitis. Cat scratch disease is best diagnosed with serological tests, using either an indirect fluorescence or an enzyme immunoassay serologic test for B. henselae. If a biopsy is obtained, the organism can be identified by a Warthin-Starry silver impregnation stain.
The disease is usually self-limited, resolving spontaneously in two to four months. If antibiotic treatment is considered - in our case because of the location and the size of the mass - trimethoprim-sulfamethoxazole, rifampin (Rifadin Hoechst Marion Roussel) and azithromycin may be effective against B. henselae.
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