CME ArticleNeutrophilic Infiltrates in Panniculitis: Comprehensive Review and Diagnostic Algorithm ProposalLlamas-Velasco, Mar MD*; Fraga, Javier MD†; Sánchez-Schmidt, Júlia-María MD‡; Fernández-Figueras, Maite MD§; Gallardo, Fernando MD¶; Rütten, Arno PhD‖; Kempf, Werner PhD** Author Information *Dermatologist, Dermatology Department, Hospital Universitario de la Princesa, Madrid, Spain; †Head of Department, Pathology Department, Hospital Universitario de la Princesa, Madrid, Spain; ‡Pathologist, Pathology Department, Hospital Del Mar, Barcelona, Spain; §Head of the Department, Pathology Department, Hospital Universitari General de Catalunya-Grupo Quirón Salud, Barcelona, Spain; ¶Dermatologist, Dermatology Department Hospital Del Mar, Barcelona, Spain; ‖Dermatologist and Dermatopathologist, Dermatopathologie Friedrichshafen/Bodensee, Friedrichshafen, Germany; and **Dermatologist and Dermatopathologist, Kempf und Pfaltz Histologische Diagnostic, Zürich, Switzerland. Correspondence: Mar Llamas-Velasco, MD, Dermatology Department, Hospital de La Princesa, C/Diego de León 62, CP 28006 Madrid, Spain (e-mail: [email protected]). All authors, faculty, and staff in a position to control the content of this CME activity and their spouses/life partners (if any) have disclosed that they have no financial relationships with, or financial interests in, any commercial organizations relevant to this educational activity. The American Journal of Dermatopathology: October 2020 - Volume 42 - Issue 10 - p 717-730 doi: 10.1097/DAD.0000000000001597 Buy CME Test Metrics Abstract Neutrophilic infiltrates in panniculitis can be seen in different clinical–pathological entities. There are a “mostly neutrophilic inflammatory infiltrate” in some entities classically defined as neutrophilic panniculitis and already included in algorithms, such as enzymatic panniculitis, infective and factitial ones, erythema induratum, or subcutaneous Sweet syndrome, but there are also other panniculitis where neutrophils are frequently observed such as panniculitis associated with inflammatory bowel disease or rheumatoid arthritis, or drug-induced panniculitis associated with BRAF inhibitors, and finally, some panniculitis are better classified in other panniculitides groups but may present with neutrophil-rich variants, such as the neutrophil-rich subcutaneous fat necrosis of the newborn. We review the main clinical and histopathological features of most of these panniculitides and construct a diagnostic algorithm including these diseases. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.