Table 1: Histological differences between granuloma annulare (GA)  and necrobiosis lipoidica diabeticorum (NLD) (adapted & modified from Ref: 9,10)

Histological Characteristics

Granuloma annulare

Necrobiosis Lipoidica

Epidermis

Normal

Most often atrophic or acanthotic

Predilection of lesion

Mainly in superficial dermis

Mainly in deep dermis +/- subcutis

Necrobiosis

In descrete foci

Diffuse, marked and ill-defined

Palisading of histiocytes

Marked

Varied and not well identified; diffusely sparse histiocytes

Vascular changes

Absent capillary hyperplasia and perivascular lymphocytic cuffing

Variable capillary hyperplasia & occlusive vascular changes

Fibrosis

Absent

Common fibrosis plus necrosis

Giant-cells

Relatively few; Tuberculoid & sarcoidal features uncommon

Common Giant-cells and tuberculoid & sarcoidal features

Fat*

+/- (occasional)

++ (common)

Mucin**

++ (common)

+ (variable)

* Deposition of extracellular lipid droplets in necrobiotic foci (best seen with oil red O)

** Deposition of mucopolysaccharides in necrobiotic foci (best seen with Alcian blue)