Background:Diagnosis of panniculitis (Pn) is associated with significant difficulties due to the variety of etiological factors, which include panniculitis-like T-cell lymphoma (PLTСL) – a rare variant of non-Hodgkin lymphoma.Objectives:to study clinical and laboratory features of PLTСL in rheumatology.Methods:Over 8 years PLTСL was diagnosed in 10 patients (9 women and 1 man, average age 37.2 ± 7.4) who were referred to V.A. Nasonova Research Institute of Rheumatology with a diagnosis of erythema nodosum or panniculitis. In addition to general clinical study, serum concentrations of α-1 antitrypsin, amylase, lipase, ferritin, creatine phosphokinase, immunological parameters (ANF-Hep2, dsDNA, C3 and C4 complements, CRP, ANCA, Scl-70, antibodies to cardiolipins G and M) were determined, and positron emission tomography combined with computed tomography (PET-CT), histological and immunohistochemical examination (IHC) of the biopsy sample of skin with subcutaneous fat from the affected areas were performed.Results:The clinical picture of PLTСL was characterized by generalized red-crimson moderately painful (VAS pain intensity 45mm) subcutaneous nodes on the upper limbs and trunk (100%), face (60%) and lower extremities (75%), without ulceration and oily fluid leakage. A “trembling saucer” symptom was evident in 75% of the observed cases. All patients had febrile fever. No enlargement of the lymph nodes of the liver and spleen was observed. The blood test revealed leukopenia (up to 2.0·x 109 /l) in 50% of cases, an increase in ESR and CRP by three or more times in 100% of cases. The biochemical blood test demonstrated an increase in LDH activity by two or more times in all patients. PET-CT in 100% of cases revealed an intense accumulation of 18F-FDG in the nodes which correlated with a high proliferative activity index. The morphological picture resembled lobular panniculitis without vasculitis. Tumor lymphocytes had an immunophenotype of cytotoxic T-lymphocytes: CD3+, CD8+, granzyme B+. To confirm the tumor nature of the infiltrate the rearrangements of the T-cell receptor genes were studied. Glucocorticoid therapy (23.5±9.6 mg/day) was ineffective which required polychemotherapy in most patients.Conclusion:PLTСL presents a complex diagnostic task that requires a multidisciplinary approach to verify the diagnosis and treatment tactics.Disclosure of Interests:None declared