Chest radiographs may be normal in some patients with pulmonary tuberculosis, an occurrence that has been noted with increasing frequency. To characterize the clinical features in patients with pulmonary tuberculosis and normal chest radiographs, Marciniuk and colleagues performed a retrospective study of 25 patients with normal chest films and culture-positive pulmonary tuberculosis.

The authors reviewed the records of a tuberculosis control program in Saskatchewan, Canada, to identify patients with culture-positive tuberculosis. Between 1988 and 1997, 518 cases of tuberculosis were diagnosed. Of these, 25 patients had normal findings on chest films, for an incidence of 4.8 percent.

The mean age of the patients with normal chest films was 26 ± 13 years (age range: six months to 59 years). In 22 cases, tuberculosis was diagnosed by positive sputum cultures. In the remaining three cases, the diagnosis was made by gastric washings. The results of the Mantoux skin test were recorded in 23 patients; the mean size of induration was 19 mm. However, four patients had no evidence of induration. (In the 493 patients with abnormal radiographic findings, no induration was found in 5 percent.)

The most common symptoms exhibited by the patients with normal chest films were cough (76 percent), sputum production (64 percent) and night sweats (24 percent). Anorexia was present in 20 percent, fever of more than one week's duration in 20 percent and weight loss in 16 percent. Twenty-four of the patients were noted to have a cough for more than one month, fever for more than one week or a skin-test conversion after contact with a person known to have active tuberculosis. Only two patients reported no symptoms; they were identified by contact tracing.

To examine whether the number of patients with tuberculosis who have normal chest films is increasing, the authors analyzed the data from three periods. The incidence of negative chest films and culture-positive pulmonary tuberculosis was 0.7 percent for 1988–89, 3.5 percent for 1990–91 and 10 percent for 1996–97.

The authors conclude that in their population, the occurrence of normal chest films in patients with active tuberculosis is not uncommon. A likely explanation for the increased incidence of this type of presentation may be improved detection of early disease. The authors believe the results suggest that sputum smear and culture for Mycobacterium tuberculosis should be obtained in patients who have normal chest films but present with a cough lasting for more than one month or fever lasting for more than one week or who have a documented skin-test conversion less than two years after exposure to infectious tuberculosis.

editor's comment: This is a provocative study, but the results must be interpreted within the clinical context. The patients were members of a highly select group who had been referred to a centralized tuberculosis program in Canada. The authors mention in their discussion that one reason for the observed increased incidence of normal chest radiography in patients with tuberculosis may have been the development in the mid-1990s of improved techniques for isolating and growing M. tuberculosis. Obtaining sputum cultures in all patients who present with only one of the three clinical features in this study may not as a general rule be clinically prudent or cost-effective. The appropriateness of such an approach would depend on the patient population. On the other hand, earlier diagnosis of tuberculosis leads to fewer contacts, decreased morbidity and usually better outcomes.—j.t.k.