Usefulness of skin immunofluorescence for distinguishing SLE from SLE-like renal lesions: a pilot study.

Lupus nephritis (LN) may represent a diagnostic problem, particularly in pediatric patients that present with typical histological lesions but do not fulfill the American Rheumatism Association (ARA) criteria for the diagnosis of systemic lupus erythematosus (SLE). Based on the well-described deposition of immunoglobulins (Ig) and complement at the dermoepithelial junction in SLE, we hypothesized that skin biopsies may help in the diagnosis of LN. To test this hypothesis, we carried out a pilot study, performing a skin biopsy in 22 patients with LN and 13 patients with lupus-like lesions, regardless of the time elapsed from onset of renal disease. The latter group of patients was further divided into a purely renal group, designated as isolated full-house nephropathy (FHN), and a dubious cases group, presenting with additional clinical and biological features consistent with SLE but insufficient for diagnosing SLE. None of the 6 isolated FHN patients had positive skin immunofluorescence. Conversely, 5/7 patients in the dubious cases group (p<0.02) and 13/22 in the LN group (p<0.002) had positive staining for C1q, and 5/7 patients in the dubious cases group (p<0.02) and 16/22 patients in the LN group (p<0.001) had positive staining for IgM. No correlation was observed with the time elapsed from the initial diagnosis. These data suggest that skin biopsies may help distinguishing LN from isolated FHN. In addition, they identify an intermediate group of patients with evidence of systemic involvement despite the absence of a sufficient number of ARA criteria to be labeled as SLE.