C1q deposits at the dermoepidermal junction: A marker discriminating for discoid and systemic lupus erythematosus

Discoid lupus (DL) and systemic lupus erythematosus (SLE) patients have been comparatively evaluated for complement and immunoglobulin deposits at the dermoepidermal junction (DEJ) by immunofluorescence (IF). When IF was positive, C1q deposits were quasi-constantly found in SLE patients with or without skin lesions (90%), while C1q was found in only 29% of the DL patients. Of the 42 DL patients followed-up for at least 2 years, 4 have eventually evolved a systemic disease. In these 4, neither cryoglobulinemia nor significant titers of ANA had been found at the time of presentation. Only 1 of these 4 patients had initially circulating immune complexes (P.E.G.) and a positive IF in a normal sunprotected area. C1q deposits at the DEJ were present in all these 4. Of the remaining 38 DL patients, none has progressed to SLE: 8 had had significant titers of ANA, 5 had had circulating immune complexes, and 3 others had had cryoglobulinemia. Thus C1q deposits in DL cases are associated with a relatively high incidence of eventual systemic disease. Taken together, these data suggest that C1q deposits in skin may be a marker for systemic lupus.