Diagnostic utility of kidney biopsy in patients with sarcoidosis and acute kidney injury

BACKGROUND Sarcoidosis is an idiopathic multisystem disease characterized by noncaseating granulomatous inflammation. Renal biopsy is often performed to evaluate the patient with sarcoidosis and acute kidney injury (AKI). Diagnosis rests on the demonstration of noncaseating granulomas and exclusion of other causes of granulomatous inflammation. This paper reports a patient with pulmonary sarcoidosis and AKI whose renal function improved after prednisone therapy despite the absence of kidney biopsy findings characteristic of sarcoidosis. CASE REPORT A 63-year-old Caucasian male with history of hypertension was treated for pulmonary sarcoidosis with a 6-month course of prednisone. His creatinine was 1.6 mg/dL during the course. Two months after finishing treatment, he presented with creatinine of 4 mg/dL. A kidney biopsy was performed, which showed nonspecific changes without evidence of granuloma or active interstitial inflammation. He was empirically started on prednisone for presumed renal sarcoidosis, even with a nondiagnostic kidney biopsy finding. Within a month of treatment, his serum creatinine improved to 2 mg/dL, though not to baseline. He continues to be stable on low-dose prednisone. With this case as a background, we aimed to determine the incidence of inconclusive kidney biopsies in patients with sarcoidosis presenting with AKI and to identify the various histological findings seen in this group of patients. METHODS In this retrospective study, all patients who had native renal biopsies read at The Ohio State University over the period of 6 years were identified. Those patients with a diagnosis of sarcoidosis, presenting with AKI, were included for further review. RESULTS Out of 21 kidney biopsies done in patients with sarcoidosis over a period of 6 years, only four (19%) showed granulomatous interstitial nephritis (GIN). An equal number of patients (4 [19%]) had presence of membranous nephropathy. Nephrocalcinosis was seen in three patients (14%). Almost half of the biopsies had findings suggestive of diabetic nephropathy or other nonspecific changes not characteristic of renal sarcoidosis (48%). CONCLUSION Renal sarcoidosis can be focal in nature and characteristic lesions can be missed in a small-needle core biopsy. Inconclusive renal biopsies with only nonspecific findings are frequent in patients with sarcoidosis and AKI. The presence of GIN on renal biopsy, although classic, is uncommon. Renal sarcoidosis remains a presumptive clinical diagnosis and empiric treatment with steroids may be initiated in cases with a strong clinical suspicion even in the absence of characteristic renal biopsy findings.