Case Number : Case 2566 - 07 May 2020 Posted By: Saleem Taibjee

Rheumatoid nodules 

Alcian??

OK, Vincenzo. As requested! Alcian blue x 2 areas

sub cutaneous Granuloma annulare

If we can rule out mycobacterial infections, this can be either rheumatoid nodule (if history of rheumatoid arthritis) or deep GA. Anatomic site is good for rheumatoid nodule.

Juxta-articular GA (Pseudorehumatoid nodule). But clinical correlation and other ancillary tests to exclude Rheumatoid nodule, and also Fite to exclude atypical mycobacterial infection. 

Agree with Colleagues!!!

Agree with all of you guys. Deep GA vs. Rehumatoid Nodule. Thanks for sharing. Beautiful!!!

Thanks for the interesting comments. 

Yes, the main differential diagnosis in this case is deep granuloma annulare vs rheumatoid nodule. In fact, this case was understandably originally signed out as Rh nodule by the original pathologist.

The table from McKee is shown below showing the main discriminating features between palisading granulomatous inflammation.

As you can see, detection of mucin (either on H&E or Alcian blue) can be very helpful in deep GA. This case also had sarcoidal features, which is a further variation of GA histologically. I also show the Martius Scarlet Blue below, which seems negative i.e. no evidence of fibrin, as would be perhaps expected if Rh nodule.

It later transpired, once the patient was seen in Dermatology, that the patient had a polymorphous cutaneous picture (see example photo below of annular plaques in this patient), much more in keeping with GA. Interestingly other biopsies on this patient showed more 'conventional' GA or 'interstitial' GA patterns. A good example of the need for clinical correlation and multiple biopsies.

Lovely! CPC is the key in dermatopathology!

Nice case and interesting learning points. 

Thanks a lot for sharing this case Dr

Retrospective must we have also thought of epithelioid sarcoma in DD. i sew there is no atypia, inputs welcome

Awesome case. Thanks Dr. Taibjee!