What percentage of patients taking procainamide, hydralazine isoniazid or anti TNFα therapy develops a positive ANA? What percentage of patients develops systemic DILE?
Nearly 75% of patients receiving procainamide therapy will develop a positive ANA test within the first year of treatment, and over 90% develop a positive ANA by 2 years, yet only 20% develop DILE. In contrast, 30% to 50% of patients taking hydralazine will demonstrate a positive test after a year of drug therapy with 5% to 10% developing DILE, especially if they are slow acetylators. Up to 15% of patients on isoniazid develop a positive ANA, but few develop symptoms of DILE. Finally, between 13% and 83% of patients on anti-TNFα therapy develop a positive ANA (most commonly infliximab), but few develop DILE. Therefore, it is important to note that many more patients will demonstrate a positive ANA test than develop DILE, and the presence of a positive ANA test without symptoms is not a valid reason for stopping the medication.