DNA skin tests in patients with definite or suspected systemic lupus erythematosus and in dermatological control patients. A long-term follow-up study.

This study presents a long-term clinical and immunological follow-up of 62 patients during 1971 and 1973, tested intradermally with DNA derived from calf thymus. The DNA skin test is positive in almost all clear-cut cases of SLE. In addition, the DNA skin test was positive in 16 patients, but the criteria for SLE were not met at the time of testing. During the follow-up, 7 out of these 16 patients developed definite SLE, 2 developed subacute cutaneous LE and 3 developed ANA-negative SLE. This suggests that a positive DNA skin test may precede the development of SLE or some of its subtypes. All our SLE patients with skin test reactivity presented cutaneous disease manifestations suggesting that similar pathogenetic mechanisms may be involved in DNA tests and natural SLE skin lesions. Because the positive DNA skin test showed correlation with ANA, anti-DNA antibodies, cryoglobulins, lupus anticoagulant and depressed C3 and C4 values, humoral factors may be partly responsible. However, DNA skin test reactivity was also positive in ANA-negative SLE, suggesting that other mechanisms may also be involved.