Thread by @ASanchez_PS

Today on #pulm consult one of my new patients came in with a history of sputum (+) for a NON-tuberculous mycobacterium, specifically, M. avium complex (MAC)! Never worked this up, so let's talk about 🗣️ Pulmonary disease in MAC 🗣️ uptodate.com/contents/overv…

First, some review. NON-tuberculous mycobacteria (NTB) are mycobacterial species other than TB & M. leprae. NTB are found kind of everywhere. The fact NTB is actually a frequent lab contaminant in conjunction with...

...the fact most lung disease caused by NTM is indolent, and the fact (+) sputum cultures may represent benign respiratory colonization makes the diagnosis of true pulmonary NTB infection tricky.

Let's take a step back from diagnosis though and, again, focus on the pulmonary manifestations of MAC. MAC as a group of mycobacteria includes species like M. avium & M. intracellulare. I'm surprised to read MAC is the most common cause of pulm disease worldwide.

There are 4 groups of pulmonary syndromes caused by MAC. The first is MAC infection in patients w/ known lung disease (eg COPD, prior TB c/b cavities, CF). "The disease resembles typical TB ... [but] symptoms are generally less severe."

In fact, you should have MAC on your DDx in a patient who was treated for active TB in the past. Relapse may be NTB instead!

The second syndrome is pulmonary MAC in those w/o known lung disease. Interestingly, this occurs predominantly in nonsmoking women >50 yoa. See: "Lady Windermere's Syndrome." In looking up more on this, actually found @AnnKumfer 😄pulmonarychronicles.com/index.php/pulm…

Radiographically, this presentation is "invariably associated w/ multiple small nodules & cylindrical bronchiectasis (often in the middle lung fields). archbronconeumol.org/en-lady-winder…

The third & fourth presentations are less common. A) Solitary pulmonary nodule resembling lung cancer. B) Hypersensitivity pneumonitis, which has a cool association w/ hot tube use. ("Hot tub lung") jmedicalcasereports.biomedcentral.com/articles/10.11…

sciencedirect.com/science/articl…

So, how do we diagnose pulmonary MAC? Given the lack of consistent imaging findings, a suspected syndrome should prompt a micro w/u. (Suspicion = chronic infiltrate +/- cavity on imaging in a pt w/ a positive pulm ROS.)

This consists of smear & culture of at least 3 separate expectorated sputum samples obtained in the morning. For pts at risk for TB or w/ compatible imaging for TB, remember to test sputum (NAAT) for TB as well!

If the etiology then remains unclear & imaging infiltrate persists, BAL and/or transbronchial biopsies may be performed.

💊 Treatment for pulmonary MAC? 💊 First, ensure compatible clinical, radiographic, microbiologic criteria are met: this Rx is prolonged, frequently difficult to tolerate, w/ modest long-term response rates.

The decision to treat is patient-centered, so see the below link for more details. If you do decide to treat, the UpToDate rec is at least a 3-drug regimen. Macrolide-susceptible? Azithro/rifampin/ethambutol. Macrolide-resistant? Consult ID. uptodate.com/contents/treat…

Where to go from here? Well, this thread is on 🗣️ pulmonary MAC 🗣️, so I'll leave the idea of disseminated-MAC disease for someone else 🙃 That said, it can go to pretty much every organ!

Apparently I can't keep a consistent thread going, so here's the rest!

https://twitter.com/ASanchez_PS/status/1313994484422635520?s=20

More on NTB here! Awesome, @AaronLTroy

https://twitter.com/AaronLTroy/status/1295017887409811456?s=20