PMC4278017_01
Features of the renal biopsy. (A) Under light microscopy (x200), the mesangial matrix was mildly increased and the interstitium was multifocally infiltrated by histiocytic collection. (B) Tubules revealed diffuse acute damage and minimal atrophy accompanied by mild interstitial fibrosis. Immunohistochemistry studies showed CD68 positivity in infiltrated histiocytes. But stain for iron and calcium were negative. (C) Using immunofluorescence microscopy (x400), mesangial staining was positive for C1q (2+). (D) Electron microscopy showed moderate effacement of epithelial foot processes. The mesangial matrix is moderately increased with a few electron dense deposits.
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F1
The final pathologic diagnosis was megalocytic interstitial nephritis accompanied by C1q nephropathy (Fig. 1).
Change in serum creatinine level (A), WBC count (B), and clinical course during hospitalization. After administration of methylprednisolone 1 mg/kg for megalocytic interstitial nephritis and severe HLH on the 38th hospital day, both oliguric AKI and severe leukocytosis were dramatically improved. S-M, Solu-Medrol  (methylprednisolone sodium succinate); BM, bone marrow.
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F2
Both oliguric AKI and severe leukocytosis were dramatically improved after steroid treatment (Fig. 2).