A case of rheumatoid neutrophilic dermatosis complicated by neutrophilic tubulointerstitial nephritis.

As an extra-articular manifestation of rheumatoid arthritis (RA), neutrophilic dermatosis may occur. Here, we report a rare case of RA complicated by both neutrophilic dermatosis and neutrophilic tubulointerstitial nephritis. In addition to polyarthritis, the patient exhibited purpura and erythema with haemorrhagic crusts and ulceration accompanied by marked neutrophilic infiltration, extending from the fingers to the forearms and from both lower legs to the toes, as well as interstitial lung disease, leading to a diagnosis of RA. After the initiation of tocilizumab, the arthritis improved. However, the skin lesions and renal function worsened. Histopathological examination of renal and skin biopsy specimens revealed prominent neutrophilic infiltration in both tissues. After ruling out infectious disease and vasculitis, the patient was diagnosed with neutrophilic dermatosis and neutrophilic acute tubulointerstitial nephritis. Following the introduction of dapsone, both the skin manifestations and renal impairment improved. This case represents a rare instance of rheumatoid neutrophilic dermatosis complicated by tubulointerstitial nephritis, highlighting the importance of targeting neutrophils in the treatment strategy based on the underlying pathophysiology.