Subpleural mononuclear cell infiltration. Significance in the differential diagnosis of pleuritis showing nonspecific histologic findings

Tenascin expression and distribution in pleural inflammatory and fibrotic diseases

We hypothesized that tenascin expression is increased in pleural inflammatory and fibrotic diseases and that its expression can be used as a marker of active pleural involvement. For this purpose we analyzed 71 histological samples of inflammatory and fibrotic pleura from patients with asbestos-induced pleural reaction (n = 6), postcardiac injury syndrome (n = 6), parapneumonic infection and/or empyema (n = 23), tuberculosis (n = 5, rheumatoid disease (n = 1), and fibrosis with inflammation of unknown etiology (n = 30). All 71 cases were studied by immunohistochemistry for tenascin. In 19 selected cases tenascin mRNA in situ hybridization was also performed. In every case, tenascin was increased by immunohistochemistry. Most prominent immunoreactivity was detected in areas of newly formed fibrosis. Increased tenascin mRNA expression by in situ hybridization was detected in the individual cells of the newly formed fibrosis underneath the fibrinous exudate. The tenascin mRNA-positive cells localized in areas in which by immunohistochemical studies the cells were positive for alpha-smooth muscle actin, desmin, and vimentin, suggesting a myofibroblast phenotype. Tenascin mRNA expression was also seen less frequently in areas in which some cells were positive for cytokeratin. These cells might represent mesothelial cells entrapped in the inflammatory lesion. Alternatively, they might represent fibroblast-type cells with aberrant cytokeratin expression. We conclude that in pleural inflammatory and fibrotic diseases tenascin immunoreactivity is increased and tenascin mRNA-positive cells localized mainly in the areas of myofibroblast- and, less often, mesothelial-type cells, suggesting that mainly myofibroblasts and, less commonly, also mesothelial cells might be responsible for tenascin expression in pleural inflammatory and fibrotic diseases. (J Histochem Cytochem 48:1257-1268, 2000)

Quantitation in inflammatory pleural disease to distinguish tuberculous and paramalignant from chronic non-specific pleuritis

AIM

To determine by morphometry if pleural biopsies with the histopathological diagnosis of "non-specific pleuritis", malignant, and tuberculous disease could be distinguished morphologically from those with truly non-specific disease.

METHODS

Each pleural biopsy was reviewed taking into account three compartments of reference: the visceral/parietal mesothelial compartment, the submesothelial screen compartment, and the submesothelial adipose tissue compartment. Normal connective tissue, granulation tissue, fibrocellular proliferation, fibrin, polymorphonuclear cells, mononuclear cells, and mesothelial cells were measured using conventional point counting procedures in terms of the fractional area occupied by each parameter within each compartment of reference. Ranking was carried out on 164 patients, based on their diagnosis: chronic non-specific disease (n = 57), tuberculosis (n = 27), malignant disease (n = 58), and conditions associated with transudative effusions (n = 22).

RESULTS

Stepwise discriminant analysis of the resulting data showed that biopsies from patients with tuberculosis, malignant disease, and chronic non-specific disease could be distinguished between themselves and normal cases. Statistical differences among the four groups were observed for eight morphometric parameters related to components of inflammation and extension throughout the three pleural anatomical compartments. A robust discriminant function permitted an adequate classification of the three groups of disease in 88.41% of the cases. Pleural biopsies with fibrin incorporated within granulation tissue on the submesothelial screen compartment showed 100% specificity for patients with tuberculosis, while mononuclear cells in a band-like infiltrate on the submesothelial adipose tissue compartment showed 93.1% specificity for patients with malignant disease. The truly non-specific pleuritis was characterised by deposits of fibrin in the subpleural compartment and discrete signs of chronic inflammation and reparatory fibrosis on the submesothelial screen.

CONCLUSIONS

Morphometric analysis of pleural biopsies may be a useful supplementary histological procedure to support the diagnosis of pleural tuberculosis and malignant disease.