Adipose Tissue in Multiple Symmetric Lipomatosis Shows Features of Brown/Beige Fat

INTRODUCTION: Multiple symmetric lipomatosis (MSL) (syn.: Launois–Bensaude Syndrome, benign symmetric lipomatosis) is a rare disease of fatty tissue. The pathophysiology of MSL still remains unclear, although several approaches have been described in order to understand it. Beside morphological characteristics and some molecular cell biological approaches, little is known about the histological and immunohistochemical characterization of adipose tissue from patients with MSL. METHODS: From the 45 patients with MSL in our database, 10 were included in the study. Fat tissue samples were collected from affected and unaffected areas. The forearm served as a control area as this area is not affected in MSL. The specimens were analyzed after selected stainings were taken (hematoxylin–eosin = HE, Elastica van Gieson, Ladewig, CD200, CIDEA, myf5, p107, Prdm16, Sca-1, syndecan, UCP1, MAC387, Glut4). RESULTS: In patients suffering from MSL, no macroscopic or microscopic morphological difference could be found between affected and unaffected adipose tissue in HE stainings. The majority of samples showed positivity for UCP1 (9/10 clinically affected tissues, 7/10 clinically unaffected tissues) and CD200. CONCLUSION: Marker profiles support the hypothesis that affected adipose tissue derives from brown or beige adipose tissue rather than from white fat. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00266-020-01666-6) contains supplementary material, which is available to authorized users.