A 4-year-old girl is brought to the clinic by her parents due to painful swelling in her groin, which began 2 weeks ago and has gradually become red and tender. Cool compresses and over-the-counter analgesics have not improved her symptoms. The patient attends preschool 3 times a week and returned from a family trip to China 2 months ago. The family has 2 dogs, a cat, and a turtle. Temperature is 37.4 C (99.3 F); other vital signs are normal. Examination shows a small, nontender papule on the anterior left thigh. There is a 4-cm, tender, soft, and freely mobile left inguinal lymph node with overlying erythema. Which of the following is the most likely causative organism of this patient's condition?

Question

A 4-year-old girl is brought to the clinic by her parents due to painful swelling in her groin, which began 2 weeks ago and has gradually become red and tender.  Cool compresses and over-the-counter analgesics have not improved her symptoms.  The patient attends preschool 3 times a week and returned from a family trip to China 2 months ago.  The family has 2 dogs, a cat, and a turtle.  Temperature is 37.4 C (99.3 F); other vital signs are normal.  Examination shows a small, nontender papule on the anterior left thigh.  There is a 4-cm, tender, soft, and freely mobile left inguinal lymph node with overlying erythema.  Which of the following is the most likely causative organism of this patient's condition?

Quizplus · Accepted Answer

11ec25c8_d6b4_7491_bc81_a70b08b12c42_MD0003_00 A localized papule with ipsilateral regional lymphadenopathy in the setting of cat exposure raises concern for cat-scratch disease (CSD). CSD, caused by Bartonella henselae, is a fastidious gram-negative bacillus carried by the majority of cats, especially kittens. B henselae can be transmitted by a cat scratch or bite, or (rarely) by a flea. However, the majority of patients do not recall a specific scratch or bite. Classically, patients present with a localized papular or nodular skin lesion that may initially go unnoticed. Additional presenting symptoms may include fever of unknown origin and/or regional lymphadenopathy in the subsequent 1-2 weeks. Affected lymph nodes are enlarged, tender, and have overlying erythema; suppuration is less common. Lymphadenopathy may take 1-2 months to resolve. Cat exposure and symptoms consistent with CSD are usually sufficient to make a clinical diagnosis. Although many mild cases will self-resolve, treatment with azithromycin is typically recommended. (Choice B) Mycobacterium tuberculosis should be considered in patients with lymphadenopathy (especially cervical) or who have traveled to an endemic region (eg, China). Similar to CSD, the onset may be gradual; however, adenitis due to M tuberculosis is strikingly nontender. (Choice C) Pasteurella multocida, normal oral flora in dogs and cats, can cause cellulitis and other soft tissue infection within 1-2 days of a dog or cat bite. This patient's adenopathy with indolent onset is inconsistent with P multocida. (Choice D) Salmonella enteritidis is carried by reptiles (including turtles) and can cause severe mesenteric adenitis in conjunction with enteritis. Cutaneous lesions are inconsistent with Salmonella infection. (Choices E and F) Staphylococcus aureus and Streptococcus pyogenes are common causes of acute bacterial lymphadenitis, which presents with a warm, tender, erythematous lymph node. However, this child's papular skin lesion and gradual symptom onset are inconsistent with acute bacterial lymphadenitis. Educational objective: Cat-scratch disease, caused by Bartonella henselae, most commonly presents with a mild papular or nodular skin lesion and ipsilateral lymphadenitis of gradual onset. These symptoms in the setting of cat exposure are sufficient to make a clinical diagnosis of cat-scratch disease. References: Cat-scratch disease. (http://www.ncbi.nlm.nih.gov/pubmed/21243990)

A 4-Year-Old Girl Is Brought to the Clinic by Her