We describe the case of a patient with known history of psoriasis that presented with 1 year of unexplained fever, muscle weakness and marked weight loss, suspicious for B symptoms of a malignant origin. [$^{18}F$]-Fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) scans demonstrated an unusual serpiginous pattern of uptake in the fascia and muscles as well as lymph node activity. Multiple histological samples, including a final PET-probe guided lymph node surgical resection, excluded malignancy and confirmed the diagnosis of reactive inflammatory changes, with a plausible diagnosis of autoimmune lymphoproliferative syndrome with associated lymphadenitis, fasciitis and myositis, possibly mediated by tumor necrosis factor (TNF) inhibitor. To our knowledge, there is no evidence of a previously reported FDG uptake pattern of fascia and muscle involvement in psoriatic arthritis.