PAN and p-ANCA

[csmith1]

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Just checking to be sure...

BRS Path (and FA, since it merely repeats BRS) say p-ANCAs are associated with polyarteritis nodosa. Robbins and Cecils Essentials of Medicine say p-ANCAs are associated with microscopic polyarteritis and NOT with PAN.

i don't remember seeing this brought up on BRS Path error threads...

 

[FoxyDoc]

As far as I understand it, p-ANCAs are indeed associated with PAN. BRS and First Aid are correct.

 

[Idiopathic]

Microscopic polyangitis is a subset of PAN, and both are associated with p-ANCA.

 

[csmith1]

Well, I hope the powers that be--should they choose to ask--would use c-ANCA instead.

I hope you can see the root of my confusion here. I'm not actually losing sleep over this one, but this is doing a nice job of occupying my time rather than, ya know, studying.


Robbins Pathologic Basis of Disease, 6th ed, page 520.

Unlike microscopic polyarteritis, classic polyarteritis nodosa has little association with ANCA.

from page 521.

While classic polyarteritis nodosa is restricted to arteries, this type [microscopic polyarteritis] generally affects arterioles, capillaries, and venules, although in ususual cases arteries may be involved. Moreover, in contrast to polyarteritis nodosa, in a single patient, all lesions tend to be the same age, and ANCA are present in the majority of cases.

 

[csmith1]

I suppose that I could just be splitting hairs here, but the Robbins authors went out of their way to discuss PAN and pANCA, as did the BRS and FA authors.

 

[dredd]

Robins is technically correct. In 1994, a consensus was reached to separate PAN and microscopic polyangitiis (MPA) as two different disease processes. However, in clinical practice and in most clinical texts, MPA is still listed under PAN (with a little notation that they are actually two different diseases) because they share some of the same pathology, some of the same therapies, and clinicians are used to hearing them as the same disease process (first described in 1886, it takes a while for change in nomenclature to take in medicine). First Aid and BRS are not incorrect though, because a significant number of patients with PAN and not MPA still positive P-ANCA's (just not nearly as much as MPA is associated with p-ANCA). For USMLE purposes, I would think of PAN and MPA when given a positive p-ANCA, and wegner's when given a positive c-ANCA, although there is a significant amount of overlap. Remember that these are auto-antibodies that we are using a lab tests to help diagnose patients, they play some role in the auto-immune pathology, but they do not represent the complete picture of what is occuring on a molecular level (there are a lot of different autoimmune antibodies associated with each condition, many of which we do not have standardized tests for yet). Here's something from e-medicine to give you an idea of the numbers:
"Antineutrophil cytoplasmic antibodies: Approximately 20% of patients with classic PAN are positive for P-ANCA. In patients with MPA, 40% are positive for C-ANCA (antiproteinase 3), 50% are positive for P-ANCA (antimyeloperoxidase), and 10% are negative for ANCA. This is compared with persons with Wegener granulomatosis, in which 75% are positive for C-ANCA, 20% are positive for P-ANCA, and 5% are negative for ANCA"
http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&dopt=Abstract&list_uids=94175958