Acute Interstitial Nephritis – AKI

00:01 So this again is under our intrinsic renal diseases, moving on with our acute interstitial nephritis.

00:06 It really is marked by an inflammatory cell infiltration in the kidney interstitium that's caused by an immune process.

00:14 So it could be medications that are causing this and the typical culprits are going to be NSAIDs, so this is the third time I'm now mentioning NSAIDs and how they are not the friend of a nephrologist.

00:24 These are penicillins, cephalosporins, sulfonamides, rifampin, we can see this with the fluoroquinolones as well like ciprofloxacin and proton pump inhibitors.

00:37 I should say that proton pump inhibitors really have been quite interesting over the last several years.

00:42 They don't always cause an acute allergic interstitial nephritis but we do see a correlation with a subacute rising creatinine and the use of these PPIs and the thought process is that there is a hypersensitivity reaction ongoing with this causing an underlying allergic interstitial nephritis.

00:58 Now we can also see this immune response with autoimmune diseases, things like Sjogren's syndrome or things like sarcoidosis.

01:07 And then finally, infection in the kidney.

01:10 Things like legionella, some of our atypical bacterias, leptospirosis and then viral infections like CMV.

01:19 For now, we're gonna focus on our medication-induced or drug-induced AIN because that's really what's most common and that's certainly what's gonna be on your licensure exams as well as what you're gonna see in your patient population.

01:30 So the clinical presentation of patients who are coming in with an allergic interstitial nephritis from medications include typically onset or the onset typically happens about 3 to 5 days after a second exposure to drug or weeks to months after a first exposure.

01:46 So we don't tend to see that initial presentation after a first exposure, it's really after the second time that they've seen drug.

01:53 And again, it's usually 3 to 5 days afterwards.

01:56 Ideally, they have this classic triad where they present with a rash, a fever and they have eosinophilia on their differential.

02:05 But unfortunately, the full triad is only observed in about 10% of the patients so don't always count on each one of those things to be present in order for you to really clinch that diagnosis.

02:16 What we see most often is really the peripheral eosinophilia and fever.

02:22 So, when we're looking at our diagnostic workup and how we want to clinch that diagnosis, again, we're gonna be a good detective, we're gonna look at that history and chart review and specifically what we're looking at is drug exposure, a variable latency.

02:37 So, did they have medication and was there a temporal increase in that creatinine? We also wanna look at the physical exam.

02:45 Do they have a fever? Do they have that exanthematous maculopapular rash that we talked about? On laboratory evaluation, we're really again looking for that acute rise in serum creatinine temporally correlating with drug administration.

02:59 We're also looking for peripheral eosinophilia on the blood smear.

03:03 And sometimes we may see an eosinophiluria .

03:08 And oftentimes those urine eosinophils will be greater than 1% and although ideally if we could see that, that would be great.

03:14 But one thing that I'd like to mention is that the sensitivity and specificity of eosinophiluria for AIN is actually on the lower side.

03:22 Secondly, unless you're at certain institutions, by the time you order and get this test back, it's not gonna be that meaningful cause your patient will have already probably been through their course.

03:33 Proteinuria, we can see in our patients typically it's gonna be less than 1 g/day and again, this typically is tubular proteinuria.

03:42 And then the urine sediment, these are the things again that I get excited about looking at as a nephrologist, so what I'm looking for in specific are white blood cells which are pictured here on the right and you can also sometimes be lucky enough to see white blood cell casts.

03:56 So again what happens here is our white blood cells are collecting in the tubule.

04:00 They're combining with that Tamm-Horsfall protein and they form this beautiful cylindrical cast that you can see in the urine sediment.

04:08 So if I really want to be definitive and I wanna know what the diagnosis is without a doubt, oftentimes, I might need to do a renal biopsy.

04:15 And I'll explain why that's important, it really has to do with our treatment.

04:19 So, if my patient has AIN, allergic interstitial nephritis then the first thing I wanna do is I really wanna remove the offending drug.

04:28 Why am I gonna biopsy the patient? What if my patient is in the ICU? They have a multi-drug resistant organism.

04:35 And they're on an antibiotic that I think is implicated in causing their allergic interstitial nephritis.

04:40 It's a life threatening infection, so if I'm about to tell my infectious disease doctor or my other colleagues that I want to remove this drug, I need to be very sure that that drug is causing allergic interstitial nephritis in my patient so a biopsy might be warranted in that situation.

04:56 And always, the approach is whenever you're in this situation, to work in a multi-disciplinary team, I'm working with infectious disease, I'm working with my trauma surgeons or anybody who is taking care of this patient because we're all coming together to find the right option in order to both improve the renal failure but also save this patient's life.

05:16 If my patient, if I've removed the drug and they continue to have ongoing renal failure then I might think about a short course of steroids.

05:25 Typically, if I'm going to do this, the patient needs to have AIN for less than 2 weeks in order for this to work.

05:31 If it's been ongoing for longer than that, then the likelihood of steroids making an impact in your patient's course is much less so.

05:38 And again, I would never do this in a siloed fashion, I always wanna do this in a multi-disciplinary approach.

05:45 I wanna be talking with my infectious disease doctors and the other doctors who are taking care of this patient to ensure that the therapy that I'm giving isn't going to harm them further.