[A case of nephrotic syndrome associated with severe interstitial pneumonitis due to cyclophosphamide whose life was saved by steroid pulse therapy].

A 53-year-old man was admitted for treatment of nephrotic syndrome due to membranous nephropathy. Since he did not improve with prednisolone alone, cyclophosphamide was administered concomitantly. However, this induced severe interstitial pneumonitis, which was not cured by discontinuation of the drug, but disappeared completely with six episodes of methylprednisolone pulse therapy. The incidence of cyclophosphamide-induced interstitial pneumonitis is low, but the mortality is high. Since cyclophosphamide is often used for the treatment of nephrotic syndrome, attention should be focused on the incidence of interstitial pneumonitis. Discontinuation of cyclophosphamide and intensive therapy are required when it occurs.