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Cat scratch disease and acquired immunodeficiency disease: diagnosis by transmission electron microscopy
J G Guccion1, C L Gibert, L G Ortega
1Pathology and Laboratory Medicine Service, Department of Veterans Affairs Medical Center, Washington, DC, USA.
Insights
This case highlights how transmission electron microscopy aided in diagnosing cat scratch disease (CSD) in an HIV-positive patient. Light microscopy was inconclusive, underscoring the value of advanced imaging for rare bacterial infections.
Area of Science:
- Medical Microbiology
- Immunology
- Pathology
Background:
- Human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS) can alter lymph node architecture.
- Cat scratch disease (CSD) is a bacterial infection typically diagnosed via clinical presentation and serology, but can be challenging in immunocompromised individuals.
- Lymphadenopathy with atypical cells can mimic lymphoma, complicating diagnosis.
Purpose of the Study:
- To present a case where advanced microscopy was crucial for diagnosing CSD.
- To illustrate the diagnostic challenges of CSD in the context of advanced HIV infection.
- To emphasize the utility of transmission electron microscopy (TEM) in identifying microorganisms missed by light microscopy.
Main Methods:
- Light microscopic examination of a lymph node biopsy.
- Special histochemical stains (including Warthin-Starry stain).
- Transmission electron microscopy (TEM) of lymph node tissue.
Main Results:
- Light microscopy showed effaced lymph node architecture with atypical reticulum cells, granulomatous inflammation, fibrosis, and vascular proliferation, suggestive of lymphoma.
- Microorganisms were not visualized with light microscopy or special stains.
- TEM revealed clusters of small, pleomorphic bacteria within degenerated collagen and blood vessel walls, confirming CSD.
Conclusions:
- TEM is invaluable for diagnosing CSD, particularly when light microscopy findings are ambiguous or mimick other conditions like lymphoma.
- HIV/AIDS can present with atypical lymph node pathology, necessitating advanced diagnostic techniques.
- This case underscores the importance of considering CSD in patients with relevant exposure history and unexplained lymphadenopathy, even with advanced immunosuppression.
Abstract:
A 33-year-old, homosexual, cat-owning, African-American man with human immunodeficiency virus infection by positive serologic tests and acquired immunodeficiency syndrome by CD4 lymphocyte count alone (39 cells/mL) presented with a one-year history of intermittent fever, weight loss, and generalized lymphadenopathy. A malignant lymphoma was suspected clinically. Light microscopic study of a left inguinal lymph node biopsy specimen revealed effacement of the lymph node architecture by a diffuse infiltrate of large, atypical reticulum cells, loose, patchy granulomatous inflammation, diffuse hyaline fibrosis, diffusely proliferated blood vessels, and multifocal degeneration and necrosis. Lymph follicles were absent and lymphocytes were moderately depleted. Microorganisms were not seen in lymph node sections stained with special histochemical stains (including the Warthin-Starry stain). These light microscopic changes were considered suggestive of a malignant lymphoma, especially Hodgkin's disease. The diagnosis of cat scratch disease (CSD) became apparent only after transmission electron microscopic study of the lymph node revealed clusters of small, pleomorphic bacteria in degenerated collagenous tissue and in blood vessel walls. This case illustrates the value of transmission electron microscopy in making the diagnosis of CSD, especially when light microscopic changes are superimposed on those of late human immunodeficiency virus infection of the lymph node.
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