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Azathioprine and Tubulointerstitial Nephritis in Henoch-Schönlein Purpura To the Editor: We read with interest the report of Bir, et al, which suggests that azathioprine might have induced tubulointerstitial damage in their patient1. We have also experienced similar cases in patients with severe Henoch-Schönlein nephritis (HSN) treated with azathioprine2. We reported that azathioprine might be an effective therapy in children with severe HSN by ameliorating the progression of immunologic renal injury2. Nevertheless, 2 of the 10 patients with HSN who had been treated with azathioprine showed definite tubulointerstitial nephritis at followup biopsy. In these 2 patients, massive proteinuria rapidly improved after cessation of azathioprine therapy, and one of them also showed decreased mesangial depositions of IgG, IgA, IgM, and C3 at a second biopsy. However, mild proteinuria had persisted throughout the course of the disease, which might be related to tubulointerstitial nephritis. Although it is very difficult to prove that azathioprine might have caused severe tubulointerstitial damage, our patients did not receive any other nephrotoxic drugs, and the duration of severe proteinuria was not long enough to cause such a tubulointerstitial injury. However, we detected the tubulointerstitial nephritis by renal biopsy at the end of the course of azathioprine treatment, because our cases did not show the characteristics of rapidly progressive renal failure. Therefore, clinicians should be more cautious in their use of azathioprine in patients with vasculitis, and further studies should be performed to elucidate the relationship between azathioprine and tubulointerstitial nephritis. JAE IL SHIN, MD; JAE SEUNG LEE, MD, Department of Pediatrics, Institute of Kidney Disease; HYEON JOO JEONG, MD; Department of Pathology, Yonsei University College of Medicine, 134 Shinchon-Dong, Seodaemun-Ku, 120-752, CPO Box 8044, Seoul, Korea. E-mail: jsyonse@yumc.yonsei.ac.kr REFERENCES 1. Bir K, Herzenberg AM, Carette S. Azathioprine induced acute interstitial nephritis as the cause of rapidly progressive renal failure in a patient with Wegener's granulomatosis. J Rheumatol 2006;33:185-7. 2. Shin JI, Park JM, Shin YH, et al. Can azathioprine and steroids alter the progression of severe Henoch-Schonlein nephritis in children? Pediatr Nephrol 2005;20:1087-92.
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