Patch-type granuloma annulare: An institution-based study of 23 cases.

Background: Granuloma annulare (GA) is a skin disorder of uncertain etiology. Patch (type) GA is an uncommon variant of GA with a paucity of data characterizing it. We describe the features of 23 cases of patch GA.

Methods: The archives of dermatopathology were searched for cases of patch GA. The clinical history and morphology for each patient were reviewed. Only cases with patch clinical morphology were included. The clinical and histopathologic features were assessed including the pattern of granulomatous inflammation and presence of other inflammatory cell types.

Results: Most patients were female (19/23) with erythematous patches on the trunk and proximal extremities. The most common clinical differential diagnosis included mycosis fungoides (MF), morphea and contact dermatitis. Dyslipidemia was the most common comorbidity (30%), followed by diabetes (15%) and hypertension (15%). Histopathologic features included interstitial lymphocytes and histiocytes with dermal mucin. Two cases showed focal palisaded granulomas. Eosinophils and plasma cells were present in 1/3 of cases.

Conclusion: Patch GA is an uncommon GA variant with an interstitial granulomatous histopathologic pattern that predominantly affects women over 50. It can mimic interstitial MF and early morphea both clinically and histopathologically. Awareness of this GA variant can help prevent misdiagnosis and inappropriate treatment for these patients.