How does interstitial granulomatous dermatitis compare to gr...

How does interstitial granulomatous dermatitis compare to granuloma annulare?
Granuloma annulare and interstitial granulomatous dermatitis may appear similar clinically and histologically. Granuloma annulare also presents with papules and plaques, but these are typically on the back of the hands or feet, whereas the trunk is a more common site for interstitial granulomatous dermatitis. Granuloma annulare is less often associated with autoimmune diseases.

The characteristic histological features of granuloma annulare are:

*Histiocytes located in the upper dermis
*Rare or absent neutrophils and eosinophils
*Abundant mucin.

How is interstitial granulomatous dermatitis diagnosed?

Interstitial granulomatous dermatitis is diagnosed by a pathologist on examining a skin biopsy. The characteristic histological features of interstitial granulomatous dermatitis are:

*Dense histiocytic inflammation in the reticular (lower) dermis
*Sparse neutrophils and eosinophils
*Perivascular and interstitial lymphocytes
*Interstitial histiocytes (between the collagen bundles) or palisaded histiocytes (lined up perpendicular to fragmented central collagen).
*Focal degeneration of collagen, which may be surrounded by space (floating sign)
*Few giant cells.