Cat-Scratch Disease Presenting as a Popliteal Mass

AUTHORS:
Roger Nicome, MD¹ • Ankhi Dutta, MD, MPH² • Hatel Moonat, DO³

AFFILIATIONS:
¹Section of Pediatric Hospital Medicine, Department of Pediatrics, Texas Children’s Hospital and Baylor College of Medicine, Houston, Texas
²Section of Pediatric Infectious Diseases, Department of Pediatrics, Texas Children’s Hospital and Baylor College of Medicine, Houston, Texas
³Section of Hematology and Oncology, Department of Pediatrics, Texas Children’s Hospital and Baylor College of Medicine, Houston, Texas

CITATION:
Nicome R, Dutta A, Moonat H. Cat-scratch disease presenting as a popliteal mass. Consultant. 2022;62(2):e17-e19. doi:10.25270/con.2021.05.00004

Received December 28, 2020. Accepted January 18, 2021. Published online May 12, 2021.

DISCLOSURES:
The authors report no relevant financial relationships.

CORRESPONDENCE:
Roger Nicome, MD, Texas Children’s Hospital and Baylor College of Medicine, 1102 Bates Street, Suite 1860, Houston, TX 77030 (rknicome@texaschildrens.org)

A previously healthy, 13-year-old boy presented to our hospital with a painful mass in the left popliteal fossa. Approximately 3 weeks prior to presentation, he had reported injuring his left lower extremity while trying to avoid a fall from an all-terrain vehicle (ATV). He had reported some pain but no swelling at the time. A few days later, he sought care from the emergency department (ED) because of persisting pain.

History. Initial plain radiology scans had showed possible Osgood-Schlatter disease, so the boy was discharged with supportive care and an outpatient referral to a sports medicine physician. A noncontrast magnetic resonance imaging (MRI) scan of the knee was performed 1 week later, results of which showed a peripherally lobulated, T2 hyperintense soft tissue mass at the posterior aspect of the distal femoral metaphyseal region measuring 4.5 × 3.8 × 3.4 cm, which was inseparable from portions of the gastrocnemius muscles and raised concern for malignancy. An additional, smaller mass measuring 1.7 cm was noted above the larger mass.

The patient returned to the ED approximately 5 weeks from his initial presentation and was admitted to the hospital for further evaluation. Hospital radiologists then confirmed the findings from the MRI scan performed at the outside facility, with additional suggestion that the mass could also represent conglomerated lymph nodes. At that time, the patient had clinically endorsed worsening of pain and swelling to the point of walking with a limp. He denied fevers, weight loss, night sweats, and exposure to tuberculosis or sick contacts. However, he did report an exposure to a stray kitten approximately 6 weeks prior to his initial ATV injury and 2 weeks prior to admission. 

Physical examination. The patient’s vital signs on admission were stable, and physical examination findings were only significant for the palpable firm left popliteal fossa mass, which was tender to touch and measured approximately 3 to 4 cm in diameter without any overlying erythema, warmth, or associated left knee swelling. The tenderness limited the patient’s full knee extension.

Diagnostic tests. Initial results from laboratory studies revealed a normal complete blood cell count, an elevated C-reactive protein level of 2.9 mg/dL, a normal lactic dehydrogenase level of 503 U/L, and a normal uric acid level of 4.9 mg/dL. Results of a peripheral blood smear did not show evidence of a hematologic malignancy.

A repeat MRI of the left knee with and without contrast again showed an inflammatory popliteal mass confined to the posterior soft tissues measuring 8.2 × 3.5 × 3.7 cm with some areas of central necrosis (Figures 1 and 2). Because of the knee pain, MRI scans of the patient’s hips and pelvis were also conducted, results of which identified multiple benign-appearing, inguinal and external iliac chain lymph nodes in the left hemipelvis, raising suspicion for a possible infectious etiology vs a neoplastic process (Figure 3).

Figure 1. A T2 fat-saturated sagittal MRI scan demonstrated confluent popliteal fossa masses (arrows) with juxtalesional inflammatory changes.

Figure 2. A T1 fat-saturated axial MRI scan after the administration of intravenous contrast demonstrated solid enhancement in the deep components of the popliteal fossa mass (arrow), as well as more superficial components demonstrating central nonenhancement consistent with liquefaction/necrosis (arrowhead).

Figure 3. A magnetic resonance imaging scan of the hip after administration. Contrast of the hip demonstrated external iliac and inguinal lymph nodes.

Infectious diseases and oncology specialists were consulted to assist with further work-up, including Bartonella serologies and a computed tomography scan of the chest/abdomen/pelvis. Results were unremarkable except for prominent reactive lymph nodes below the diaphragm. Ultimately, a biopsy of the mass was recommended for a definitive diagnosis because of its unusual location and size.

The patient underwent an outpatient tissue biopsy 1 week later. Results of the biopsy sections and smears revealed granulomatous inflammation with necrosis and neutrophils, as well as with rod-shaped bacteria highlighted by Warthin-Starry stain. The level of serum Bartonella henselae immunoglobulin G (IgG) was elevated at more than 1:1024, and the level of IgM was low at less than 1:64. Results of aerobic, anaerobic, mycobacterial, and fungal cultures from the biopsy specimen were negative. A Bartonella polymerase chain reaction (PCR) test conducted on the tissue returned negative results as well.

In the interim, the patient was started on oral azithromycin, 500 mg, on day 1 followed by azithromycin, 250 mg, on days 2 to 5. Treatment was extended to 10 days due to persistent swelling. He followed up at our infectious diseases clinic at the end of the course, with his mass significantly reduced in size. During a phone follow-up visit 2 weeks later, the patient’s mass had fully resolved, and he had no other systemic signs or symptoms.

Discussion. Presented is a case of popliteal lymphadenitis secondary to cat-scratch disease masquerading as a popliteal mass. Patients with cat-scratch disease usually have cervical, axillary, or inguinal lymphadenitis. Popliteal lymphadenitis has not been extensively reported in the pediatric literature except for isolated case reports.^1,2 The presence of popliteal lymphadenitis should prompt the exploration of differential diagnoses and additional evaluation where warranted. It could be a harbinger of neoplasm, or the result of other infectious etiologies such as bacteria (Staphylococcus aureus or Group A Streptococcus), mycobacteria (Mycobacterium tuberculosis or nontuberculous mycobacteria), and less likely, viruses.^3,4

Cat-scratch disease is usually a self-limited condition caused by infection with B henselae. Most cases (85%-90%) are mild and characterized by regional lymphadenopathy or lymphadenitis, which appears 1 to 2 weeks after infection.^1,2 In about 10% to 15% of patients, however, more-severe disseminated disease can occur, leading to infections of the visceral organs (hepatosplenic disease), eyes (Parinaud oculoglandular syndrome), or the central nervous system (encephalitis, aseptic meningitis).^4,5 The common sites of lymphadenitis include the cervical, axillary, or inguinal areas that contain nodes that drain the inoculation site.⁶ Other sites of lymphadenitis are far less common, confusing the clinical picture.

Cat-scratch disease is usually diagnosed based on the characteristic clinical presentation.^6,7 Cats are natural reservoir of Bartonella, and 13% to 90% of stray and domestic cats are reported to be seroprevalent in the United States.⁶ The time from exposure to the appearance of lymphadenopathy can vary from 5 to 50 days (median, 12 days).⁶ Given such a wide range of time, kitten exposure is an important piece of historical data that may be missed if patients and their families are not questioned about remote exposures or exposures outside of the immediate surroundings. Although the most common presentation of cat-scratch disease is axillary and cervical lymphadenitis, the presence of kitten exposure—even if remote—and a popliteal mass should raise concern for cat-scratch disease.^1,2

Atypical presentations of cat-scratch disease have also been reported in the literature. In a study of 22 immunocompetent patients, 16 had presented with asymmetric local lymphadenopathy, 1 patient with prolonged fevers and 5 with atypical presentations resembling an oncologic process (1 with parotid mass, 3 with bone mass, and 1 with a cervical mass).⁴ Other studies have reported paravertebral masses and breast masses related to cat-scratch disease.^8,9 All of the patients in these studies had undergone a tissue biopsy, which showed granulomatous inflammation, supported by a positive serological test for Bartonella. Bartonella DNA PCR tests were also performed to confirm the diagnoses.

Once there is a presumptive diagnosis of cat-scratch disease, serologic testing is often performed to confirm the diagnosis but should not delay treatment in patients with the typical clinical features. Tissue biopsy may also be needed to rule out neoplasm and show evidence of granulomatous inflammation. Within the granulomas, B henselae bacteria appear as pleomorphic bacilli in chains or clumps on the Warthin-Starry stain. Tissue PCR tests for Bartonella are commercially available and have high specificity but variable sensitivity.⁷

Patients with symptomatic cat-scratch disease must be treated quickly. Treatment is centered around symptom relief and can prevent complications of dissemination.⁵ Azithromycin is the preferred treatment option, but for patients who do not respond to azithromycin, alternative antibiotics include clarithromycin, rifampin, doxycycline, or trimethoprim-sulfamethoxazole.⁶ Disseminated disease can be treated with combination regimens (eg, azithromycin or doxycycline with rifampin or gentamicin with rifampin) and should be treated in consultation with an infectious diseases specialist. Duration of treatment depends on clinical presentation and can range from days to several weeks.⁶

References

1. Schiettecatte A, Shahabpour M, Vanhoenacker FM, et al. An unusual case of cat-scratch disease of the knee: case report and differential diagnosis. JBR-BTR. 2007;90(5):391-394.

2. Begres JM, Mangus CW. The flea's knees: A unique presentation of cat scratch disease. Am J Emerg Med. 2020;S0735-6757(20)30929-3. https://doi: 10.1016/j.ajem.2020.10.033

3. Rolain JM, Lepidi H, Zanaret M, et al. Lymph node biopsy specimens and diagnosis of cat-scratch disease. Emerg Infect Dis. 2006;12(9):1338-1344. https://doi.org/10.3201/eid1209.060122

4.  Mazur-Melewska K, Mania A, Kemnitz P, Figlerowicz M, Służewski W. Cat-scratch disease: a wide spectrum of clinical pictures. Postepy Dermatol Alergol. 2015;32(3):216-220. https://doi.org/10.5114/pdia.2014.44014

5.  Nelson CA, Saha S, Mead PS. Cat-scratch disease in the United States, 2005-2013. Emerg Infect Dis. 2016;22(10):1741-1746. https://doi.org/10.3201/eid2210.160115

6. Bartonella henselae (Cat-Scratch Disease). In: Kimberlin DW, Brady MT, Jackson MA, Long SS, eds. Red Book®: 2018 Report of the Committee on Infectious Diseases. 31st ed. American Academy of Pediatrics; 2018:244-247.

7. Florin TA, Zaoutis TE, Zaoutis LB. Beyond cat scratch disease: widening spectrum of Bartonella henselae infection. Pediatrics. 2008;121(5):e1413-e1425. https://doi.org/10.1542/peds.2007-1897

8. Al-Rahawan MM, Gray BM, Mitchell CS, Smith SD. Thoracic vertebral osteomyelitis with paraspinous mass and intraspinal extension: an atypical presentation of cat-scratch disease. Pediatr Radiol. 2012;42(1):116-119. https://doi.org/10.1007/s00247-011-2087-2

9. Markaki S, Sotiropoulou M, Papaspirou P, Lazaris D. Cat-scratch disease presenting as a solitary tumour in the breast: report of three cases. Eur J Obstet Gynecol Reprod Biol. 2003;106(2):175-178. https://doi.org/10.1016/s0301-2115(02)00164-