ABSTRACT
Proteus syndrome is an extremely rare disorder that manifests as an asymmetric, disproportionate overgrowth of any connective tissue, such as bone, fat or epidermal nevi, in a mosaic or patchy pattern. It has an estimated prevalence of less than 1/1,000,000 live births. The diagnosis can be difficult because the phenotypes of the patients are variable. Many individuals develop cutaneous capillary malformation and prominent varicosities (large and complex vascular malformations). Thus, Proteus syndrome patients are at risk of developing deep vein thrombosis and pulmonary embolism. The authors present the case of a patient with Proteus syndrome who was admitted because of pulmonary thromboembolism and presented hypertrophy of the left arm and left hemithorax. LEARNING POINTS: Proteus syndrome is an extremely rare disorder that manifests as an asymmetric, disproportionate overgrowth of any connective tissue.The diagnosis can be difficult because the phenotypes are variable.It is important to keep in mind the importance of anticoagulation because patients are at risk of developing deep vein thrombosis and pulmonary embolism.