Interstitial Granulomatous Dermatitis and Palisaded Neutrophilic Granulomatous Dermatitis: Retrospective Clinicopathological Analysis of 16 Cases

INTRODUCTION: Reactive granulomatous dermatitis (RGD) is a new entity, which is highly associated with systemic disorders. There is scarce data regarding interstitial granulomatous dermatitis (IGD) and palisaded neutrophilic granulomatous dermatitis (PNGD). OBJECTIVES: We aimed to evaluate clinical and histopathological characteristics of IGD and PNGD as unified entities under the term of RGD. METHODS: Observational, retrospective, single-center study of patients diagnosed with IGD and PNGD between 2012 and 2021 were included in the study. RESULTS: Of 16 patients (14 females and 2 males) with RGD, 13 had IGD and 3 had PNGD with a mean age of 62.5 years. The most common clinical presentation was plaques 37.5% (N=6), followed by patches 25% (N=4). The most common localization of involvement was lower extremity 75% (N=12), followed by trunk and upper extremity. Multiple localization of involvement was determined in 75% (N=12) of patients. None of the patients had rope sign. Associated comorbidities such as autoimmune diseases and malignancies were detected in 68.7% (N=11) of patients. In majority of biopsies (87.5%; N=14), there were lymphohistiocytic cell infiltration. Other accompanying cells were scarce neutrophils 31.2% (N=5) and eosinophils 31.2% (N=5). All of the biopsies had interstitially located lymphohistiocytic cell infiltration surrounding with swollen and degenerated collagen. Palisaded pattern was determined in 18.7% (N=3) of patients and floating sign was seen in 18.7% (N=3) of biopsies. CONCLUSIONS: RGD is a rare entity and most patients with RGD had associated disorders such as autoimmunity or malignancy. There is overlapping between IGD and PNGD, therefore supporting the usage of umbrella term as reactive granulomatous dermatitis is compatible with the literature.