Roentgenologic Changes of the Lung Associated with Isoniazid Therapy in Pulmonary Tuberculosis

¹ The Veterans Administration Hospital, San Fernando, California, and the Departments of Medicine and Infectious Diseases, School of Medicine, University of California, Los Angeles.

1) A group of 106 patients was treated with isoniazid for a period of from three to 15 months and the roentgen effects were observed on the various types of lesions present.

2) There were 135 areas of active infiltrations divided according to their pathological characteristics and classified as exudative, exudative-productive, productive, and productive-fibroid groups, with roentgen improvement in 65, 37, 14, and 4 per cent respectively. The greatest improvement occurred in the more recent exudative lesions, in those of minimal or moderate extent, and in the streptomycin sensitive cases. Conversely, the poorest results were obtained in the older productive and fibroid lesions, in those far advanced, and in the streptomycin resistant cases. Initial roentgen changes occurred within three months, improvement continued rapidly up to about five months and thereafter at a slower but still steady rate. Such inactive infiltrations as true fibrosis and calcification were not altered in any way.

3) The 107 cavities in 81 patients were classified similarly to the infiltrations. Some reduction in size occurred in 25 cavities (23 per cent), including five closures. The productive cavities showed some decrease in size in 45 per cent, the fibroid in 7 per cent, and the others averaged 22 per cent. Apart from the five closures, the average decrease in size was 35 per cent, and the great majority remained small. Here, too, the initial changes occurred within three months, reaching a maximum at six months for 75 per cent of the cavities. Closed cavities were smaller than the others, but those showing only a partial decrease averaged the same size as those not responding at all. Better results were obtained in those cases sensitive to streptomycin than in those resistant to it.

4) The significant point of isoniazid resistance appeared to be at 5 mcg. Both infiltrations and cavities began to show improvement and reached initial rapid peaks within six months, corresponding roughly to development of full resistance to 5 mcg. isoniazid. After this period the cavities continued to show improvement in only 25 per cent, while almost all the infiltrations continued to show further benefit. It seems that, in the case of infiltrations, the benefit initiated by isoniazid was continued by natural factors, whereas, in the case of cavities, the initial changes produced by the drug included local mechanical alterations which operated within the shorter period of six months.

5) Symptomatic improvement occurred in almost all of the patients showing roentgen improvement and in 60 per cent of those showing no x-ray change.