Tolvaptan and Autosomal Dominant Polycystic Kidney Disease.

n engl j med 368;13 nejm.org march 28, 2013 1257 macrophage activation syndrome. In animals, high levels of interleukin-6 contribute to the triggering of this syndrome1; additional cytokines, including interferon-γ, interleukin-1, and interleukin-18, might be involved in maintaining and amplifying the inflammatory response.2 Indeed, interleukin-1 antagonism may be beneficial in a full-blown case of the macrophage activation syndrome.3 Regarding the possible role of tociliz umab in masking the symptoms of this syndrome, the five patients with the macrophage activation syndrome reported by Shimizu et al.4 had mild laboratory abnormalities representing either blunted cases of the macrophage activation syndrome, possibly consistent with the abovementioned role of interleukin-6 in the triggering of the syndrome, or part of the known side effects of tocilizumab (i.e., increased aminotransferase levels and neutropenia). Long-term vigilance on the rate and features of the macrophage activation syndrome during tocilizumab treatment will provide additional useful information for clinical practice. Fabrizio De Benedetti, M.D., Ph.D.