Granulomatous interstitial nephritis: a chameleon in a globalized world

Have we missed AINything? Acute interstitial nephritis in SARS-CoV-2 infection and vaccination

Acute interstitial nephritis (AIN), defined by the presence of interstitial inflammation accompanied by tubulitis, is an often overlooked cause of acute kidney injury (AKI). It is now well established that SARS-CoV-2 infection can cause a wide variety of kidney injuries, most commonly acute tubular injury and collapsing glomerulopathy. In comparison, AIN is rarely documented in association with SARS-CoV-2 both anecdotally and in larger series of autopsy or biopsy studies. In this issue of the Journal, León-Román describe 5 cases of AIN in patients with a history of COVID-19 and highlight AIN as a possibly under-reported or ignored facet of renal disease associated with SARS-CoV-2. They describe three scenarios in which AIN can be seen: 1) SARS-CoV-2 infection after diagnosis of AIN, 2) AIN followed by SARS-CoV-2 infection in the same admission and 3) Severe SARS-CoV-2 and AIN possibly associated with SARS-CoV-2 itself. Overall, AIN remains rare in SARS-CoV-2 and causality is difficult to ascertain. Interestingly, AIN is not only seen in association with the disease itself but also with SARS-CoV-2 vaccination. This scenario is equally rare and causality is no less difficult to prove. A history of preceding SARS-CoV-2 infection and vaccination should be actively sought when patients present with otherwise unexplained AIN.

A non-immunocompromised host with nontuberculous mycobacteria-associated tubulointerstitial nephritis

A 50-year-old man was admitted to our hospital with the complaints of fever and general malaise. He had no history of human immunodeficiency virus (HIV) infection or treatment with immunosuppressive agents. We performed renal biopsy to investigate possible acute kidney injury. Pathological findings showed inflammatory cell infiltration, including granulomatous lesions in the interstitium. We diagnosed the patient with acute granulomatous tubulointerstitial nephritis. We initiated prednisolone (PSL) 40 mg/day (0.6 mg/kg), in combination with isoniazid for a latent tuberculosis infection, because of positive results in interferon-γ release assays. The patient's fever and malaise promptly disappeared, and his renal function improved. After the patient had been discharged, Mycobacterium intracellulare grew in cultures of his renal tissue and urine. We gradually reduced the dose of PSL; we initiated combination therapy with ethambutol, clarithromycin, and rifampin. After 2 years of follow-up, the patient continued treatment for chronic kidney disease; it has since enabled him to avoid renal replacement therapy. This report describes a rare instance of nontuberculous mycobacteria-associated tubulointerstitial nephritis in a patient without a history of HIV infection or organ transplantation. In differential diagnosis of granulomatous tubulointerstitial nephritis, clinicians should consider drugs, sarcoidosis, tubulointerstitial nephritis and uveitis syndrome, vasculitis, and infections (e.g., involving mycobacteria). Prompt microbiological examinations, especially of urine or biopsy cultures, are vital for diagnosis.

[Renal granulomatous nephritis: Histopathological point of view]

Granulomatous interstitial nephritis (NIG) is a rare form of interstitial nephritis that can be related to acute or chronic clinical presentation. NIG is characterized by granulomas located to the renal interstitium and composed of either epithelioid histiocytes with giant cells and/or of foreign body reaction. The symptoms are unspecific and associate varying degrees of renal failure with abnormal urinanalysis. Extra-renal signs may point to systemic disease. Pathological examination from kidney percutaneous biopsy or surgical resection is required to assert NIG diagnosis and to guide the etiological research. The main causes of NIG are sarcoidosis, drug reactions, mycobacterial infections and crystalline nephropathies. Sarcoidosis is characterized by non-necrotic and well-formed giant cell epithelioid interstitial granulomas. Drug reactions have less well-defined granulomas with inconstant eosinophils. The presence of caseous necrosis within giant cell and epithelioid granulomas leads to infectious NIG diagnosis (tuberculosis and fungal infection). Identification of crystals within foreign body reaction can be improved by polarized light study. Xanthogranulomatous pyelonephritis and malakoplakia are rarer causes of NIG characterized by patches of histiocytes associated with inconstant giant cells. Differential diagnoses of NIG are represented by granulomatous reactions centered on glomeruli and vessels (vasculitis and emboli of cholesterol crystals). Less than 10% of NIG are idiopathic. The prognosis and the treatment vary according to the cause. The factors of poor renal prognosis are chronic irreversible tubulo-interstitial injury (tubular atrophy and interstitial fibrosis).

HIV, drugs and the kidney

Human immunodeficiency virus (HIV) affects over 36 million people worldwide. Antiretroviral therapy (ART) is expanding and improving HIV viral suppression, resulting in increasing exposure to drugs and drug interactions. Polypharmacy is a common complication as people are living longer on ART, increasing the risk of drug toxicities. Polypharmacy is related not only to ART exposure and medication for opportunistic infections, but also to treatment of chronic lifestyle diseases. Acute kidney injury (AKI) is frequent in HIV and is commonly the result of sepsis, dehydration and drug toxicities. Furthermore, HIV itself increases the risk of chronic kidney disease (CKD). Drug treatment is often complicated in people living with HIV because of a greater incidence of AKI and/or CKD compared to the HIV-negative population. Impaired renal function affects drug interactions, drug toxicities and importantly drug dosing, requiring dose adjustment. This review discusses ART and its nephrotoxic effects, including drug–drug interactions. It aims to guide the clinician on dose adjustment in the setting of renal impairment and dialysis, for the commonly used drugs in patients with HIV.

AIN’t got no easy answers: recent advances and ongoing controversies around acute interstitial nephritis

Acute interstitial nephritis (AIN) is a common cause of acute kidney injury that was first described in 1898. It is most commonly caused by drugs and infections, although other aetiologies are implicated. Here we review two papers published in this issue of Clinical Kidney Journal and provide an update on current advances and controversies relating to AIN. Nussbaum and Perazella describe the diagnostic tools (namely urinary and serum biomarkers) available for AIN and highlight that there is no single test that can accurately predict the diagnosis. As such, renal biopsy remains the gold standard. Wendt et al. present findings from a 20-year retrospective study of biopsy-proven AIN. They found that a high degree of inflammation was associated with a greater chance of renal recovery, in contrast to the presence of cortical scars, which were associated with a worse outcome. There was also a significant number who required renal replacement therapy. They advocate the use of a scoring system for AIN to help direct management. We also discuss new drugs associated with AIN (in particular new anticancer drugs) and unusual forms including granulomatous AIN. Finally, we discuss the opportunities for future research and how this may impact clinical practice.

Single-centre experience of granulomatous interstitial nephritis-time for a new approach?

Background: Differentiating between renal-limited sarcoidosis and tuberculosis (TB) infection as a cause of granulomatous interstitial nephritis (GIN) can be difficult. This series compares clinical features and response to treatment between the different underlying aetiologies in order to propose a management algorithm for GIN to assist with diagnosis and treatment.

Methods: This retrospective study reports on all patients presenting with a histological diagnosis of GIN between 2000 and 2012 at our unit.

Results: Twenty-one patients were identified, 57% were male and the mean age was 53 years. Eight cases were associated with sarcoidosis with evidence of extra-renal disease and five with renal-limited sarcoidosis. Five patients had GIN that may have been related to TB infection or to renal-limited sarcoidosis, and three were idiopathic or drug related. All those with sarcoidosis were treated with steroids and renal function, as measured by estimated glomerular filtration rate (eGFR), improved from a mean of 24 mL/min at baseline to 37 mL/min at 1 year. Baseline eGFR was 19 mL/min in those with possible TB infection. Four received steroids as well as anti-TB drugs. Anti-TB therapy was delayed in four patients by a mean of 22 months due to difficulties in diagnosis. Two patients with TB developed end-stage kidney disease and the remaining three patients had a mean eGFR of 28 mL/min at 1 year.

Conclusions: This series represents the largest cohort of patients with GIN in the UK and supports previous findings that patients with sarcoid have a favourable outcome with steroid treatment. Those with TB have an inferior prognosis, perhaps due to delayed diagnosis. We suggest an algorithm when investigating a diagnosis of GIN with the aim of expediting diagnosis and considering a trial of anti-TB therapy in order to prevent deterioration of renal function.