Just updated the chapter on ANCA vasculitis and this field is frankly a mess. It feels like vasculitis is so scary it's pushed people into a hyper-aggressive approach despite poor evidence: 😬 PLEX: Not supported by the largest & best RCT (PEXIVAS). But lots of articles still suggest it for patients with scary high creatinine levels, which doesn't really make biological sense (either it treats the underlying disease process or it doesn't). Different centers either believe or don't believe in this - see article clip below. 😬 Pulse-dose steroid: Everyone admits there's no data to support this (see recent blog on emcrit). But it's still often recommended at doses ranging from 500-1000 mg methylpred for duration of 1-3 days. 😬 Avacopan was accepted based on an RCT which was apparently manipulated to manufacture a positive result. It was adopted into guidelines. Then the RCT was retracted and now the whole literature around this is hopelessly confounded.

New IBCC chapter on CT scan for patients with a history of contrast allergy 😁 Some key points: ☢️ If contrasted CT is emergently necessary (e.g. stroke, trauma) just get it. Full stop. ☢️ If the contrast allergy reaction occurred before 2000 it's likely due to oudated high-osmolal contrast dye. You don't need to worry about this, just get the scan. (Canadian guidelines) ☢️ Define the severity of the prior reaction. Unless it was *severe* and resembling an allergy (e.g. anaphylaxis, vital sign abnormalities) you don't need to really worry about it. ☢️ Antihistamines *do* probably reduce the risk of mild contrast reactions (e.g., urticaria). If you want to give a dose of oral nonsedating antihistamine that's fine (eg cetirizine 10 mg PO). Antihistamines don't save lives or prevent anaphylaxis. And you don't need to give a big bomb of IV diphenhydramine. ☢️ The best available data suggests that pre-scan steroids don't prevent severe reactions. Canadian guidelines say not to give steroids. Historically the American Allergy guidelines have also recommended not giving steroid. The most recent American College of Radiology plus American Allergy consortium guidelines (below) say to "consider" steroid (figure below). That means exercise your best judgement about risks vs benefits. ☢️ If you do decide to give steroid you can give a single dose of 200 mg IV hydrocortisone or 40 mg IV methylprednisolone 4-8 hours before the CT scan. You don't need to give multiple doses of steroid. You don't need to wait a billion hours before the scan. Hydrocortisone probably makes the most pharmacokinetic sense because it's relatively short-acting and has low CNS penetration (less delirium). ☢️ Changing to a different formulation of contrast dye DOES probably help *if* you can get this done. Unfortunately patients often don't know what type of contrast dye they received previously. Also, most hospitals only have access to a couple types of contrast dye. So this works better in theory than reality. ☢️ No matter what you do there is always a nonzero risk that the patient may develop anaphylaxis after CT scan. This should be treated aggressively with epinephrine per usual. There's no way to get the patient to zero risk. Trying to get to a zero-risk situation will actually cause delays and harm. #1/2 (link in next post)