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PubMed This is a summary of 15 peer-reviewed journal articles Updated
Infectious Disease

Biology & Diagnostic Clues

At a Glance

Swollen lymph nodes in cat-scratch disease (CSD) indicate an active immune response, not a serious condition like cancer. Doctors use specific imaging features and pathology tests to confidently distinguish CSD from lymphoma and tuberculosis.

When a lymph node swells to a noticeable size, the primary concern for many patients and parents is often lymphoma (a type of cancer) or a chronic infection like tuberculosis (TB) [1][2]. Understanding why the body reacts this way to Bartonella henselae can help clarify why doctors look for specific “signatures” to tell these conditions apart.

The Biological Response: Why Nodes Swell

Swollen lymph nodes, or lymphadenopathy, are not a sign that the bacteria are winning; they are a sign that your immune system is working [3].

When the bacteria enter through a scratch, they travel through the lymphatic system—a network of vessels that acts like the body’s drainage system [3]. The bacteria reach the nearest lymph node, which acts as a “security checkpoint” [4]. Here, your immune cells trap the bacteria and begin a fierce counterattack [5]. This battle causes the node to become inflamed and enlarged—a process known as granulomatous inflammation [6].

Telling the Difference: CSD vs. Other Conditions

Doctors use a combination of history, imaging, and lab tests to distinguish CSD from more serious look-alikes. They look for specific “fingerprints” rather than relying on a single test.

1. Lymphoma

Because CSD can look like lymphoma on a scan, doctors look for benign (non-cancerous) markers [1].

  • The “Hilar” Signature: On an ultrasound, a healthy or “reactive” lymph node usually keeps its bright fatty center (hilum) [7]. In lymphoma, this structure is often distorted or destroyed [8].
  • Fluid Movement: On an MRI, doctors can see that water molecules move more freely in a CSD node compared to a dense, crowded cancerous growth [9].

2. Tuberculosis (TB) and NTM

Both CSD and TB create clumps of immune cells called granulomas, but they look different under a microscope [2].

  • Stellate Microabscesses: A classic “fingerprint” of CSD is the stellate microabscess—a star-shaped pattern formed by the immune system [10][11].
  • Special Stains: Pathologists use special staining techniques to highlight the specific bacteria under the microscope, confirming whether it is Bartonella or the bacteria that cause TB [12][13].

3. Tularemia

Tularemia is another infection humans can get from animals that causes similar swelling [14]. Doctors rule this out by asking about exposure to wild animals (like rabbits) or ticks, and by using specific blood tests [14].

Summary of Diagnostic Clues

Feature Cat-scratch Disease Lymphoma Tuberculosis (TB)
Typical History Kitten scratch/bite [3] Night sweats, weight loss Exposure to TB, chronic cough
Node Appearance Tender, may feel warm [15] Firm, painless, “rubbery” Firm, may form a “mat”
Ultrasound Preserved fatty center [7] Lost/distorted center [8] Matted nodes, fluid pockets

While the initial sight of a swollen node is alarming, these specific medical clues help your care team confirm that the body is simply reacting to a common infection [1].

Common questions in this guide

Why do lymph nodes swell in cat-scratch disease?
Swollen lymph nodes are a sign that your immune system is actively fighting the Bartonella henselae bacteria. As immune cells trap the bacteria in the lymph node, the area becomes inflamed and enlarged.
How do doctors tell the difference between cat-scratch disease and lymphoma?
Doctors use imaging like ultrasound and MRI to look for benign markers. In an infection like cat-scratch disease, the lymph node usually keeps its normal fatty center, whereas lymphoma often destroys or distorts this structure.
What is a stellate microabscess on a pathology report?
A stellate microabscess is a distinctive star-shaped pattern of immune cells seen under a microscope. It is a classic fingerprint of cat-scratch disease that helps pathologists distinguish it from other infections like tuberculosis.
Will a biopsy rule out tuberculosis and cancer?
Yes, examining lymph node tissue or fluid can definitively rule out other conditions. Pathologists use special stains and PCR tests to identify the specific bacteria causing the infection and ensure no cancerous cells are present.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What specific features on the imaging (ultrasound, CT, or MRI) point toward an infection like CSD rather than a malignancy?
  2. 2.If we are unsure of the diagnosis, would a needle aspirate or a full node biopsy be more helpful in ruling out lymphoma or TB?
  3. 3.Can we perform a Bartonella-specific PCR test on the tissue to get a more definitive answer than the blood test?
  4. 4.How do you distinguish this from other 'cat-related' illnesses, like tularemia or toxoplasmosis?

Questions For You

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References

References (15)
  1. 1

    Cat Scratch Disease as a Mimicker of Malignancy.

    Dhal U, Hicklen RS, Tarrand J, Kontoyiannis DP

    Open forum infectious diseases 2021; (8(11)):ofab500 doi:10.1093/ofid/ofab500.

    PMID: 34926712
  2. 2

    Coexistence of cat scratch disease lymphadenitis and active pulmonary tuberculosis in an immunocompetent host - a case report with metagenomic diagnosis and literature review.

    Wang X, Chen S, Yang C

    Frontiers in medicine 2025; (12()):1667171 doi:10.3389/fmed.2025.1667171.

    PMID: 41140651
  3. 3

    Seasonality of Bartonella henselae IgM and IgG Antibody Positivity Rates.

    Theel ES, Ross T

    Journal of clinical microbiology 2019; (57(12)) doi:10.1128/JCM.01263-19.

    PMID: 31533982
  4. 4

    Uncovering the truth about cat-scratch disease.

    Puspitasari Y, Khairullah AR, Raharjo HM, et al.

    Open veterinary journal 2025; (15(5)):1895-1906 doi:10.5455/OVJ.2025.v15.i5.5.

    PMID: 40557109
  5. 5

    Broadening the Morphologic Spectrum of Bartonella henselae Lymphadenitis: Analysis of 100 Molecularly Characterized Cases.

    Jabcuga CE, Jin L, Macon WR, et al.

    The American journal of surgical pathology 2016; (40(3)):342-7 doi:10.1097/PAS.0000000000000552.

    PMID: 26551620
  6. 6

    Case Report: Co-infection with cat-scratch disease and infectious mononucleosis: a rare clinical entity.

    Huang W, Yuan J, He H

    Frontiers in pediatrics 2025; (13()):1660853 doi:10.3389/fped.2025.1660853.

    PMID: 41378194
  7. 7

    Epitrochlear cat scratch disease: unique imaging features allowing differentiation from other soft tissue masses of the medial arm.

    Bernard SA, Walker EA, Carroll JF, et al.

    Skeletal radiology 2016; (45(9)):1227-34 doi:10.1007/s00256-016-2407-6.

    PMID: 27193359
  8. 8

    [Sonographically detectable changes in abdominal lymph nodes in dogs with malignant lymphoma. Evaluation with special consideration of the Solbiati-Index].

    Eberhardt F, Köhler C, Winter K, et al.

    Tierarztliche Praxis. Ausgabe K, Kleintiere/Heimtiere 2015; (43(5)):309-16 doi:10.15654/TPK-150078.

    PMID: 26076988
  9. 9

    Lack of restricted diffusion in MR imaging as a potential differentiating tool of reactive lymph node in cat scratch disease from lymphoma or abscess.

    Chu Y, Hanumaiah R, Majmudar A, Gupta S

    Radiology case reports 2020; (15(8)):1180-1183 doi:10.1016/j.radcr.2020.05.017.

    PMID: 32547675
  10. 10

    Combined Application of Immunohistochemistry and Warthin-Starry Silver Stain on the Pathologic Diagnosis of Cat Scratch Disease.

    Peng J, Fan Z, Zheng H, et al.

    Applied immunohistochemistry & molecular morphology : AIMM 2020; (28(10)):781-785 doi:10.1097/PAI.0000000000000829.

    PMID: 31913159
  11. 11

    Clinicocytopathologic correlation in an atypical presentation of lymphadenopathy with review of literature.

    Choi AH, Bolaris M, Nguyen DK, et al.

    American journal of clinical pathology 2015; (143(5)):749-54 doi:10.1309/AJCPPSKWRX0GD8HJ.

    PMID: 25873511
  12. 12

    Disseminated cat-scratch disease presenting as nausea, diarrhea, and weight loss without fever in a heart transplant recipient.

    Antar AAR, Goyal A, Murphy K, et al.

    Transplant infectious disease : an official journal of the Transplantation Society 2017; (19(3)) doi:10.1111/tid.12678.

    PMID: 28199763
  13. 13

    Cat-Scratch Disease in an AIDS Patient Presenting with Generalized Lymphadenopathy: An Unusual Presentation with Delayed Diagnosis.

    Mantis J, Ali Y, Junejo SZ

    The American journal of case reports 2018; (19()):906-911 doi:10.12659/AJCR.909325.

    PMID: 30068900
  14. 14

    Parinaud's Oculoglandular Syndrome: A Case in an Adult with Flea-Borne Typhus and a Review.

    Dixon MK, Dayton CL, Anstead GM

    Tropical medicine and infectious disease 2020; (5(3)) doi:10.3390/tropicalmed5030126.

    PMID: 32751142
  15. 15

    Cat Scratch Disease: 9 Years of Experience at a Pediatric Center.

    Amin O, Rostad CA, Gonzalez M, et al.

    Open forum infectious diseases 2022; (9(9)):ofac426 doi:10.1093/ofid/ofac426.

    PMID: 36072697

This page explains diagnostic clues for cat-scratch disease for educational purposes only. Always consult a healthcare provider for an accurate diagnosis if you experience unexplained swollen lymph nodes.

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