Granulomatous Interstitial Nephropathy : When the Kidney Spills the Bean

ABSTRACT

Introduction: Sarcoidosis is a rare granulomatosis. The absence of well-defined criteria for definition and the existence of differential diagnosis makes the positive diagnosis difficult. Method(s) We report a case of sarcoidosis that illustrates the difficulty of this diagnosis in the presence of atypical clinical manifestations and a strong suspicion of tuberculosis. Ultimately, renal histology allowed the positive diagnosis and the response to corticosteroids confirmed it retrospectively. Result(s) Our patient was a 66 years-old female with a history of hypertension who presented with a sensory and motor polyneuropathy a couple of months after a mild COVID-19 pneumonia, hospitalized for exploration of a worsening renal function due to a tubulointerstitial neuropathy (creatinine upon admission at 250 micromol/l, eGFR = 16 ml/min/1,73m2 -MDRD). Kidney biopsy revealed an interstitial infiltrate of monocytes and fibrosis alongside non-necrotic and giant-cell epithelioid interstitial granulomas. Extra-renal signs consisted of the above-mentioned neuropathy, bilateral mediastinal adenopathies with no signs of a pulmonary disease at the bodyscan, a hepatomegaly, splenomegaly, a pleural and pericardial effusion of low abundance, and a peritoneal thickening. Bronchoscopy and bronchoalveolar washing found no evidence for malignancies and screening for mycobacterial infections by polymerase chain reaction was negative. No granulomas were found at the hepatic biopsy. Digestive tract endoscopy and biopsies showed no abnormalities. During hospitalization, the patient presented an episode of acute polyradiculonevritis confirmed by cerebral-spine fluid study and nerve conduction study results. Our patient received intraveinous immunoglobulins (IgIV) with a favorable outcome but relapsed one month later, showing signs of respiratory failure. Upon the second relapse of the chronic polyradiculonevritis and based on the absence of bacteriological and histological evidence for a mycobacterial infection and the results or the renal biopsy, the patient received high-dose corticosteroids alongside a second course of IgIV. The neuropathy regressed totally within a month with a decrease of creatinine level to 140 micromol/l (eGFR = 35ml/min/1,73m2) alongside the polyserositis and organomegaly. The final diagnosis was that of a sarcoidosis with pulmonary and renal involvement. Although the neuropathy could be considered a manifestation of sarcoidosis, its origin was intricated as post-viral original could not be formally excluded. Conclusion(s) The etiological diagnosis for granulomatous interstitial nephropathies can be challenging due to similar clinical presentations and the need to start specific treatments especially in the presence of life-threatening situations and the absence of clear criteria defining sarcoidosis further enhances the level of difficulty. No conflict of interestCopyright © 2023