Pleuritis as a manifestation of reactivation tuberculosis. PURPOSE: The purpose of this study was to determine the frequency with which tuberculous pleuritis is a manifestation of reactivation tuberculosis and to compare the clinical manifestations of reactivation tuberculous pleuritis with "classic" tuberculous pleuritis, in which chest roentgenograms reveal no parenchymal infiltrates. PATIENTS AND METHODS: We evaluated the medical records of 59 patients in whom tuberculous pleuritis was confirmed by histologic findings or mycobacterial culture. Twenty-seven patients (46%) had typical chest roentgenographic findings of reactivation tuberculosis, whereas 32 (54%) had classic tuberculous pleuritis. The clinical and laboratory features of these two groups were compared. RESULTS: Symptoms were more prolonged and pleural fluid glucose and lactate dehydrogenase concentrations were more markedly abnormal in patients with reactivation pleuritis than in those with classic pleuritis, suggesting a more chronic inflammatory process in the former group. Compared with patients with classic tuberculous pleuritis, those with reactivation pleuritis had a lower frequency of reactive tuberculin skin tests (61% versus 88%) and granulomatous pleural inflammation (25% versus 72%), but a higher bacillary burden, manifest by a higher frequency of positive sputum smears for acid-fast bacilli (50% versus 0%) and positive mycobacterial cultures from sputum (60% versus 23%) and pleural fluid (91% versus 66%). CONCLUSIONS: In contrast to previous reports, tuberculous pleuritis was a manifestation of reactivation tuberculosis in 46% (27 of 59) of patients. Tuberculous pleuritis is a more chronic process in patients with reactivation disease than in those with classic pleuritis. The lower frequency of reactive tuberculin skin tests and granuloma formation, combined with the higher bacillary burden in patients with reactivation pleuritis, suggest that these patients mount a less effective immune response to Mycobacterium tuberculosis infection than do patients with the classic form of tuberculous pleuritis. 