Immunohistochemical Confirmation of Infections

Transcription

1 Immunohistochemical Confirmation of Infections Danny A. Milner, Jr, MD, MSc, FCAP The Brigham and Women s Hospital Harvard Medical School Boston, Masschusetts USA

2 Judicious Use of Immunohistochemistry IHC has (and remains) a confirmatory test It should not be considered diagnostic Variability in tissue fixation, technique, and runs can affect outcome (minor concern) Expense does not justify routine panels Directed use based on histomorphology is required High throughput tests WILL replace IHC but, for the present, they are standard of care

3 Infectious Disease Diagnosis Step 1 Does this histomorphology represent an infection? Yes (special stains) --No (immunosuppressed?) Step 2 Are there structures present which could be an organism(s)? Organisms vs. suspicious structures? Step 3 Can the clinical, microbiology, and pathology data be integrated to generate a correct diagnosis? Consultation with clinical ID or ID pathologist* Step 4 What additional test will confirm this diagnosis? IHC vs. ISH vs. Probe vs. PCR +/- Sequencing

4 Infectious Disease Diagnosis Step 1 Does this morphology represent an infection? Step 2 Are there structures present which could be an organism(s)? Step 3 Can the clinical, microbiology, and pathology data be integrated to generate a correct diagnosis? Step 4 What additional test will confirm this diagnosis? Morphology suggests Pattern of specific bacteria but nothing on special stains Limited yeast and/or fragments of hyphal forms Questionable viral cytopathic effect Immunosuppression limited inflammation but clinical infection

5 Infectious Disease Diagnosis Step 1 Does this morphology represent an infection? Step 2 Are there structures present which could be an organism(s)? Step 3 Can the clinical, microbiology, and pathology data be integrated to generate a correct diagnosis? Step 4 What additional test will confirm this diagnosis? Immunohistochemical confirmation is especially helpful when: Culture doesn t grow or organism does not grow routinely Culture was not sent (!!!) There is clinical urgency for treatment decisions There is a clinical algorithm fed by IHC data

6 IHC Spectrum and Approach Bacterial Confirmation for disease specific pathogens Fungal Confirmation for disease specific morphology Viral Confirmation for viral cytopathic effect Parasitic Helminthes Protozoan Confirmation for species

7 Bacterial Pathogens Species confirmation is diagnostic Culture is not easily/readily available Examples Helicobacter pylori in gastric biopsies Treponema pallidum in skin lesions Other Antibodies available Chlamydia, Yersinia pestis, Mycobacterium tuberculosis

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10 Fungal Pathogens Limited fungal elements in biopsy Insufficient for morphological diagnosis Clinical history creates broad differential Fungal stain negative Culture not taken Infection not suspected In formalin before received

11 Fungal Pathogens Clinical urgency Anti-fungal choice crucial for management Two broad categories for use: Fungal hyphae for invasive disease Aspergillus sp vs. Mucormycosis vs. other Disseminated (or potentially) yeast Cryptococcus vs. Histoplasma vs. Pneumocystis PCR/sequencing rapidly becoming a more sensitive and specific method

12 Aspergillus sp Mucormycosis?

13 Cryptococcus sp Histoplasma sp Pneumocystis jiroveci?

14 Viral Pathogens Viral cytopathic effect is present Definitive vs. Highly suspicious Clinically elevated viral load Cancer-associated virus KSV, EBV*, HPV* Almost always faster than culture Restricted somewhat to viruses for which there is specific treatment Viral presence effects prognosis/outcome

15 Herpes Simplex I or II Cytomegalovirus Varicella Zoster virus?

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20 Parasitic Pathogens Helminthes Primarily a tool for research Morphology and clinical history are usually sufficient for diagnosis and treatment Protozoan Confirmation of suspicious morphology Toxoplasmosis Microglial nodules in CNS Symptomatic GI biopsies with alterations but no inflammation Giardia lamblia Gastrointestinal suspicious forms

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23 Logistic Approach to IHC Have in house routine required tests (all pathologists interpret): HSV, CMV, VZV, KSV H. pylori Faster than culture/not likely to be replaced by molecular test Identify reliable consults for rare or unusual pathogens (expert consultants): Fungal (broad spectrum, difficult antibodies) Expand your service for specific needs: Spirochetes, Toxoplasma, Giardia, etc. Dependent on your patient population

24 Summary and Conclusions IHC remains a highly useful tool do to reliability, cost, and specificity of reaction Well characterized relevant positive controls are required for proper utilization Routine IHC should be avoided IHC tests should reflect clinically relevant algorithms for each patient population