Histologic Parameters Predictive of Mycobacterial Infection

Abstract

Tissue specimens from a wide variety of anatomic locations are frequently examined for mycobacteria using a combination of cultures and special stains. Auramine-rhodamine (AR) staining is a sensitive method for detecting acid-fast bacilli (AFB) in tissue sections. We reviewed 85 AR-positive and 275 randomly selected AR-negative biopsy specimens collected during the past 2 years at the Mayo Clinic, Rochester, Minn. Pathologic diagnoses and culture results were also reviewed. The increasing number of immunocompromised patients infected with mycobacteria and the resurgence of mycobacterial tuberculosis has created the need for rapid and cost-effective methods of diagnosis. Although molecular techniques may be useful for detecting mycobacteria, direct examination and culture still have a critical role in diagnosing mycobacterial diseases. The fluorochrome stain, auramine-rhodamine (AR), is useful for detecting acid-fast bacilli (AFB) in clinical specimens and tissue sections. In some instances, pressure from clinical colleagues or prospective ordering may result in AR staining of specimens with histologic changes inconsistent with mycobacterial infection.Necrotizing granulomatous inflammation is the most common histological abnormality in patients with mycobacterial infections.1 -2 Other less common tissue reactions include nonnecrotizing granulomas, poorly formed granulomas, and even nongranulomatous acute inflammation.1 ' 3 We reviewed surgical pathology cases that were submitted for AR staining to evaluate which histologic parameters correlated best with AR and culture positivity in our practice. MATERIALS AND METHODS Case SelectionWork cards for surgical pathology specimens submitted for AFB staining by the AR method between September 1, 1994, and August 31, 1996, were reviewed. All cases in which the AR stain was positive were included. To more accurately compare the presence of AFB in the various histologic categories, approximately four negative cases for each positive case from the same period were randomly selected and reviewed. Available culture results were also reviewed. AFB SemiquantitationThe AR staining results from entire tissue sections were reported semiquantitatively as follows: negative, 331

General Principles in the Diagnosis of Infection

“…A large number of immunostains are available that can be helpful in the identification of microorganisms ( Table 2- 7). 13 Many of these are commercially available and currently enjoy wide popularity in diagnostic pathology laboratories.…”

“…An example is tuberculosis, in which biopsies can fail to demonstrate mycobacteria in almost half of cases. 7 But even in this setting, the appearance of the inflammatory response in situ should foster a working diagnosis that is often sufficiently reliable to institute empirical treatment.…”

Histopathology for the Diagnosis of Infectious Diseases

“…For example, presence of caseous granulomas hints to the infection by Mycobacterium tuberculosis. [7] Similarly, tissue infiltration with a particular type of cell, e.g., eosinophil, would go for parasitic infection. [8] Sometimes even the histopathological changes within a tissue will lead to a probable diagnosis, like in the case of Human papilloma virus (HPV) infection, where a probable diagnosis is made by a PAP smear examination of the cervix.…”

“…Although organisms cannot be seen, the pattern of granulomatous inflammation provides the first indication that mycobacteria should be considered among the differential diagnoses. [3,7] Newer Techniques: Immunohistochemistry, In Situ Hybridization and In Situ Polymerase Chain Reaction (PCR) Molecular assays increase the specificity and in some instances may increase the sensitivity of histopathologic tests. [25,26] Molecular methods of detection may be particularly useful when microorganisms are undetectable by means of histochemical staining methods, are present in low numbers, stain poorly, are uncultivable or exhibit an atypical morphology.…”

Staining for acid-fast bacilli in surgical pathology: practice patterns and variations

“…Quality control of AFB in histologic sections is not as well established or studied compared with sputum smears. In a review of tissue sections, the presence of necrotizing granulomas, followed by nonnecrotizing granulomas, was the histologic parameter that yielded the highest positivity rate for AFB and the closest correlation to positive cultures [6]. When the clinical and pathologic features of 86 solitary pulmonary granulomas were reviewed, fungal or acid-fast organisms were identified within the tissue in 60 cases (70%) [7].…”