A 28-year-old woman presents with asymptomatic firm ring-shaped lesions on the dorsal aspect of her hands and feet. The lesions are flesh-colored to violaceous, arranged in an annular pattern, and notably lack surface scaling. On dermoscopy and clinical examination, the structure marked **A** in the diagram shows the characteristic appearance of granuloma annulare. Which of the following histopathological findings would BEST differentiate this condition from necrobiosis lipoidica diabeticorum?
A. Superficial perivascular lymphocytic infiltrate with interface dermatitis
B. Central mucin deposition within palisading necrobiotic granuloma surrounded by histiocytes and lymphocytes
C. Central lipid deposition with hyalinized collagen and vascular proliferation
D. Central fibrin deposition with surrounding palisade of epithelioid cells
Explanation
Why "Central mucin deposition within palisading necrobiotic granuloma surrounded by histiocytes and lymphocytes" is right
Granuloma annulare is characterized by a distinctive palisading necrobiotic granuloma with central mucin deposition, surrounded by histiocytes and lymphocytes. This histopathological finding is the KEY DIFFERENTIATOR from necrobiosis lipoidica diabeticorum (which shows lipid deposition, not mucin) and from rheumatoid nodules (which have central fibrin). The structure marked A — annular dermal plaques without scale — reflects this underlying necrobiotic granulomatous pathology. The mucin-rich center is pathognomonic for granuloma annulare and directly reflects the necrobiotic process with matrix deposition (Bolognia Dermatology 5e Ch 93).
Why each distractor is wrong
Central lipid deposition with hyalinized collagen and vascular proliferation: This is the histopathological hallmark of necrobiosis lipoidica diabeticorum, NOT granuloma annulare. NLD shows lipid deposition and is strongly associated with diabetes, whereas GA's association with diabetes is less consistent and occurs mainly in the generalized form.
Central fibrin deposition with surrounding palisade of epithelioid cells: This describes the histology of a rheumatoid nodule, which is a common differential diagnosis for subcutaneous granuloma annulare. Rheumatoid nodules have central fibrin necrosis, whereas GA has mucin deposition.
Superficial perivascular lymphocytic infiltrate with interface dermatitis: This pattern is typical of lichen planus and other lichenoid dermatoses, which are in the differential diagnosis of annular lesions but do not show the necrobiotic granulomatous architecture of GA.
High-YieldNEET PG
Granuloma annulare = palisading necrobiotic granuloma with MUCIN (not lipid, not fibrin); localized form favors dorsal hands/feet; generalized form (>10 lesions) warrants screening for diabetes, hyperlipidemia, HIV, and malignancy.
Bolognia Dermatology 5e Ch 93; Fitzpatrick 9e
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