A 66-year-old female with a history of hypertension presented to the emergency department with one week of lower extremity edema, nausea, and vomiting. On admission, the patient was found to be hyponatremic, hypoalbuminemic, with nephrotic range proteinuria (urine protein-to-creatinine ratio of 8.5 g/g) and acute kidney injury. During the hospital course, the patient’s AKI rapidly progressed, and she showed worsening signs of fluid overload. She had no arthralgias, rash or other peripheral stigmata of an autoimmune disease. Her PTT was found to be elevated to 54.9 seconds with a normal PT/INR. A mixing study found the presence of an inhibitor. A dilute Russel’s viper venom time and a silica clotting time were abnormally prolonged, and anticardiolipin antibodies were elevated. The ANA titer was 1:640, and anti-RNP, anti-SSA, and anti-SSB antibodies were positive. A renal biopsy was done and the patient was begun on 1g methylprednisolone per day with rapid improvement of her creatinine from 4.95 to 1.33 mg/dL within three days along with normalization of her hyponatremia.
The kidney biopsy showed features consistent with focal segmental glomerulosclerosis with tubuloreticular inclusions and epithelial cell foot process defacement. In consideration of the patient’s serologies, her abnormal coagulation tests, and a family history of SLE, the patient was diagnosed with lupus podocytopathy.
Discussion:
Lupus podocytopathy is a diffuse epithelial cell foot process defacement in the setting of SLE that differentiates itself from lupus nephritis by the absence of glomerular immune complex deposits and glomerular proliferation. The pathogenesis of the disease is direct podocyte damage as opposed to being immune-complex mediated as with lupus nephritis. The mechanism is possibly related to aberrant T cell activation and functioning. The morphological features of lupus podocytopathy are similar to those seen in minimal change disease or focal segmental glomerulosclerosis. Clinically, acute kidney injury is seen in the majority of cases of lupus podocytopathy. Mild to no microscopic hematuria is found in contrast to the often large hematuria seen in lupus nephritis. Remission is achieved in the vast majority of patients after treatment with glucocorticoids, similar to treatment of adult minimal change disease. Lupus podocytopathy is an infrequent cause of renal disease in lupus, accounting for only a small percentage of cases.
Conclusions:
Hospitalists are often confronted with acute kidney injury. While prerenal causes are the most common, intrarenal causes must be considered. Lupus podocytopathy can present with AKI and nephrotic syndrome, with or without other clinical signs and symptoms of SLE. The disease can progress rapidly and is highly responsive to treatment with steroids. Clinical suspicion and pathologic confirmation are needed to avoid missing this treatable condition.