It is generally accepted that patients suffering from Mycobacterium tuberculosis infections show positive tuberculin skin tests, with certain rare exceptions. Recognized causes of these exceptions include extreme illness, whether due to extensive tuberculosis or to other severe disease, and certain viral infections, notably measles. It is not so generally recognized that a few patients with pulmonary tuberculosis, generally of rather indolent type, who are not acutely ill, persistently fail to react to tuberculin; and that the range of tuberculin sensitivity observed in patients with the more usual forms of tuberculosis is very wide.
The effect of cortisone in diminishing the size of tuberculin reactions in patients with pulmonary tuberculosis is directly related to the degree of sensitivity; reactions produced by small doses of tuberculin in patients with high sensitivity are greatly diminished or inhibited, while those produced by 100 T.U. in patients with low sensitivity are not significantly altered. Patients with tuberculosis can be desensitized to tuberculin by increasing injections of tuberculin under chemotherapy cover. In patients who have been so desensitized, the addition of cortisone to tuberculin in an intradermal test produces positive reactions in 70%. Among patients with sarcoidosis giving no reaction to 100 T.U., about half react when cortisone is added.
These observations show that in patients with sarcoidosis, a negative tuberculin test cannot be taken to exclude M. tuberculosis infection.
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