Granuloma Annulare
Epidemiology and Etiology:
- Children and young
adults mainly
- Women > men
- Unknown etiology:
- Autoimmune?
- May be a
nonspecific reaction pattern that may follow any number of diverse
processes (neutrophilic dermatitides,
insect bites, herpesvirus infections)
Common sites:
- Dorsal surfaces of
the hands, feet, arms, legs
Gross features:
- localized
- discrete and
coalescent papules in annular and polycyclic configurations
- erythematous, skin-coloured,
occasionally violaceous
- may be umbilicated
- often enlarge
centrifugally up to 5cm
- non-pruritic
- may be
subcutaneous (deep GA)
- may be
generalized, widely disseminated, giant, linear, perforating (deep GA)
Histologic features:
- fully developed
lesion:
- palisaded granulomatous
dermatitis surrounding an area of degenerated collagen
- focal, discrete,
within dermis, with intervening normal collagen
- mucin deposition within the central
degenerated collagen (alcian blue or colloidal
iron positive)
- superficial and
deep perivascular lymphocytes and macrophages
- plasma cells are
not prominent (unlike NLD)
- interstitial or
incomplete form:
- macrophages
splayed between individual collagen bundles
- increased
connective tissue mucin deposition
- little to no
collagen degeneration
- may see:
- fibrinoid necrosis within granulomas
- granulomas may extend into septae
of fat
- eosinophils in 40% - may be numerous
Immunophenotype:
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Marker:
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Sensitivity:
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Specificity:
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Molecular features:
Other features:
References: