necrobiotic granuloma

Definition : Granulomatous disorders comprise a large family sharing the common histological denominator of granuloma formation. Collagenolytic or necrobiotic granuloma is one in which a granulomatous infiltrate develops around a central area of altered collagen and elastic fibers.

The altered fibers exhibit new staining patterns, becoming either more basophilic which gives blue appearance (“blue granuloma”) or eosinophilic giving red appearance (“red granuloma”).

Conditions which exhibit blue granuloma include granuloma annulare, Wegener’s granulomatosis, and rheumatoid vasculitis, whereas red granulomas include necrobiosis lipoidica, necrobiosis xanthogranuloma, rheumatoid nodules, Churg-Strauss syndrome, and eosinophilic cellulitis (Well’s syndrome).

A collagenolytic or necrobiotic non‐infectious granuloma is one in which a granulomatous infiltrate develops around a central area of altered collagen and elastic fibers.

The altered fibers lose their distinct boundaries and exhibit new staining patterns, becoming either more basophilic or eosinophilic.

Within the area of altered collagen, there may be deposition of acellular substances such as mucin (blue) or fibrin (red), or there may be neutrophils with nuclear dust (blue), eosinophils (red), or flame figures (red).

These color distinctions can be used as a simple algorithm for the diagnosis of collagenolytic granulomas, i.e. ‘blue’ granulomas vs. ‘red’ granulomas. Eight diagnoses are included within these two groupings.

Types

 necrobiotic granuloma ( collagenolytic granuloma )

• granuloma annulare
• necrobiosis lipoidica
• necrobiotic xanthogranuloma
• rheumatoid nodule

Differential diagnosis

 deep granuloma annulare, which tends to have more mucin deposition and less fibrin
 epitheloid sarcoma

Open references

 Necrobiotic granuloma: An update. 2018.
http://www.ijdpdd.com/article.asp?issn=WKMP-0052;year=2018;volume=5;issue=1;spage=27;epage=33;aulast=Pokharel

 Collagenolytic (necrobiotic) granulomas: part II – the ‘red’ granulomas. Jane M. Lynch Terry L. Barrett. 2004
doi : 10.1111/j.0303-6987.2004.00208.x