Clinico-pathologic assessment of the value of anti-chromatin antibodies in the diagnosis of systemic lupus erythematosus and lupus nephritis

الملخص EN

Background : lupus nephritis is the major cause of morbidity and mortality in systemic lupus erythematous (SLE) patients, and renal biopsy is the most accurate method for the evaluation of the degree of renal affection.

Recent studies suggest that ant chromatin antibodies (anti-CHR) could help in early detection of lupus nephritis in SLE patients.

Objective : to assess the prevalence of serum anti-CHR antibodies in SLE patients, to evaluate their clinical significance and their value as a marker of lupus nephritis and to correlate them with histopathologically findings of lupus nephritis.

Methodology : serum anti-CHR antibodies were determined by an enzyme linked immonsorbent assay (ELISA) in 30 SLE patients, and 30 control subjects (10 cases of rheumatoid arthritis (RA), 10 cases of osteoarthritis (OA) and 10 healthy persons).

Patients and controls were also subjected to history taking, clinical examination and routine laboratory investigations including CBC, ESR, serum complement, serum cretonne, cretonne clearance ; in addition to complete urine analysis, urinary protein measurement and serum albumin.

Renal biopsy was performed on 20 patients of SLE with clinical and laboratory evidence of nephritis and examined by both light microscopy (LM) and electron microscopy (EM).

Results : Anti-CHR antibodies in SLE patients were positive in 20 / 30 (66.7 %), while they were negative in all controls including cases of RA and OA, with a 66.7 % diagnostic sensitivity and 100 % specificity.

Anti-ds DNA antibodies were detected in 13 / 30 (43.3 %) cases of SLE only, with a 43.3 % diagnostic sensitivity and 100 % specificity.

Positive results of anti-CHR antibodies were found in17 / 20 (85 %) cases of lupus nephritis (85 % diagnostic sensitivity and 70% specificity) ; whereas anti-ds DNA antibodies were detected in 11 / 20 cases (55 %) only (55 % diagnostic sensitivity and 80% specificity).

Significant positive correlations were found between anti-CHR antibodies and disease duration, disease activity, serum cretonne, clearance, proteinuria, ESR, ANA level and nephritic lesions seen in renal biopsy.

Meanwhile, negative correlations were found with blood platelets, serum albumin, serum complement C3 level (p < 0.05).

A highly significant correlation was also found between anti-CHR antibodies and disease activity score measured by ECLAM (p < 0.001).

Renal biopsy findings showed that WHO class of lupus nephritis had a significant impact on anti-CHR antibody level (p < 0.05), with the association of higher antibody levels with proliferative glomerular lesions and frequent electron dense deposits mainly in the sub endothelial location, while no significant difference was found in case of anti-ds DNA antibodies.

Conclusion : Ant chromatin antibodies are more sensitive and specific than anti-ds DNA antibodies for the diagnosis of SLE and more sensitive as regards lupus nephritis.

Moreover, serum level of anti-CHR antibodies can be a helpful test to expect the extent of renal affection and hence choose patients candidate for renal biopsy.