The Significance of the Negative Roentgenogram in the Search for Pulmonary Tuberculosis

Abstract

Reports of cases of pulmonary tuberculosis among the Armed Forces, despite the routine x-ray examination of inductees, naturally raise a question as to the effectiveness of the roentgen method for the discovery of tuberculous lesions. Criticisms of the particular procedure used, as recently voiced by Meyers (1), are not well founded, as can be attested by anyone who has had experience in an induction center. Actually, the relatively few cases subsequently discovered (2) can well be accounted for by factors other than the use of photofluorography. The addition of the skin tuberculin test, as advocated by Meyers, would scarcely contribute anything but delay to the information necessary for determining whether or not an inductee should be accepted. In assessing the various causes for the apparent failure to eliminate all cases of pulmonary tuberculosis by roentgen examination, the matter of the latent period which must exist between the inception of any disease process and its x-ray demonstration should be given consideration. That there is a delay between the onset of symptoms of disease and the first appearance of roentgen signs is well illustrated in the case of acute osteomyelitis, the time interval here being fairly accurately established. In the case of pneumonia, also, there is fairly good evidence. We have seen one case in which clear-cut roentgen findings were observed within two and a half hours after the first symptoms, but in most instances six hours appears to be the minimum (3). In pulmonary tuberculosis the onset of symptoms is less important, since it is rare that a tuberculous lesion in the lung capable of producing symptoms is not already clearly demonstrable in the roentgenogram. There is, however, a latent period between the inception of the tuberculous infection and the appearance of roentgen evidence of a lesion. The tubercles must develop, a number of them must coalesce, and an accumulation of abnormal material at least 5 mm. in diameter must ordinarily be present, before x-ray findings are diagnostic. Some years ago, in an attempt to determine the length of this latent period, we studied (4) a small number of cases in which the time of exposure to tuberculosis could be well established and in which repeated x-ray examinations had been made. In this group eleven weeks appeared to be the minimum time between the first exposure and the appearance of a nodule or other shadows less than 1 cm. in diameter. Our subsequent experience had seemed to bear out this observation until recently, when a medical student was encountered who exhibited a nodule 1 cm. in diameter, not previously present, occurring but eight weeks after a clear-cut exposure to tubercle bacilli. Barnwell (5) has recently reported some cases among nurses, in one of whom an extensive cavitating tuberculosis was seen within fifty-six days after contact.