Autoinflammatory diseases (AIDs) are defects or dysfunctions of the innate immune system that may result from monogenic or polygenic mutations. Clinically, they manifest as recurrent fever and may be associated with various clinical features, including dermatological manifestations that are readily identifiable upon physical examination. Although skin biopsies do not typically reveal pathognomonic or specific findings, they can represent a key component in the diagnostic “puzzle” of autoinflammatory diseases, as they are low-cost and widely available tests. In a retrospective observational study conducted at the autoinflammatory diseases outpatient clinic of Hospital das Clínicas, University of São Paulo, between 2007 and 2022, 83 skin biopsies from 48 patients were analyzed (Certificate of Presentation for Ethical Consideration [CAAE]: 73174223.1.1001.0068). Clinical data available in the REDCap registry were also analyzed. At least 64% of the individuals entered into the registry have at least one instance of mucocutaneous involvement. Among all the patients, only 6 had an initially suspected autoimmune disease (12.5%), whereas the remaining 42 (87.5%) had a diagnostic hypothesis of an autoinflammatory condition. Most biopsies performed were prompted by urticarial-like lesions (29; 35%) and pustular lesions (21; 25%). Of the 83 biopsies examined, 48 (58%) exhibited histopathological findings suggestive of the investigated AIDs, whereas 30 were inconsistent with the proposed diagnostic hypothesis. Despite the absence of specific histopathological findings in many cases, the evaluation of skin biopsy features contributed to the diagnosis in over half of the cases. These findings emphasize the importance of skin biopsy as a relevant complementary diagnostic tool in the context of AIDs. Additionally, we propose the use of advanced histopathological biomarkers for interferon type-1 mediated diseases and inflammasome-related AIDs. FINEP funding: 0956/24; FAPESP funding: 2023/09965-0; Instituto de Investigação em Imunologia funding CNPQ/MCTI: 408685/2024-7.
