Symptomatic renal tubular acidosis (RTA) in patients with systemic lupus erythematosus: an analysis of six cases with new association of type 4 RTA

Objectives. We have analysed the association between different parameters of renal tubular acidosis (RTA) with clinical and laboratory parameters in patients with systemic lupus erythematosus (SLE). Methods. Review of hospital database records between 1978 and 2003 revealed six SLE patients with RTA. Correlations and comparisons were done by Spearman rank correlation coefficient and the chi(2) test. Results. Four patients had hypokalaemia (type 1 RTA) and two patients had hyperkalaemia (type 4 RTA). Three patients with type 1, but no patients with type 4 RTA, had medullary nephrocalcinosis. The majority of SLE patients with distal RTA (type 1 and type 4) had nephritis with proteinuria. No seronegative SLE was noted, and all patients were negative for anticardiolipin antibodies. There was a noticeable trend of higher serum potassium levels with increased SLE Disease Activity Index (SLEDAI; P < 0.1) and nephritic manifestation (haematuria, P < 0.1). The mean SLEDAI scores were 11.75 and 27.5 for type 1 and type 4 RTA patients, respectively. Conclusions. When present in patients with SLE, classic distal RTA (type 1) is the most common. In particular, we report here for the first time two cases of type 4 RTA in SLE patients with higher SLEDAI scores than patients with type 1 RTA. Medullary nephrocalcinosis or renal urolithiasis has not been found in our patients with type 4 RTA. Higher serum potassium levels seem to be associated with higher SLEDAI scores and more severe nephritic manifestations in patients with distal RTA.