A practical approach to the clinico-pathological diagnosis of panniculitis

Panniculitides are a group of diseases characterized by an inflammatory process that originates primarily in the subcutaneous tissue. Histopathological classification of panniculitides in mostly septal or lobular types, according to the predominant localization of the infiltrate, is complemented with the eventual identification of vasculitis and the consideration of the vessel size. Additional steps involve the characterization of the inflammatory infiltrate and other findings, such as, the type of adipocyte necrosis or the presence of sclerosis, crystals and foreign bodies. Apart from this purely histopathological characteristics, clinico-pathological correlation is often required to encompass the clinical, histopathological and laboratory data in order obtain the correct diagnosis. We will review the classification of panniculitis, useful histopathological clues for their diagnosis and diagnostic algorithms that can be applied when sclerosis is present or the inflammatory infiltrate is mostly neutrophilic.