PET/CT and brown fat in the evaluation of treatment response in Hodgkin lymphoma

Radiol Bras. 2015 Nov/Dez;48(6):399–403 402 http://dx.doi.org/10.1590/0100-3984.2015.0074 tumors are constituted of plasmacytoid cells, presenting malignant degeneration and producing a specific immunoglobulin molecule. The incidence of EMP is higher in men than in women, at a 3–4:1 ratio, most frequently occurring around the age of 50– 60. It is estimated that such tumor represents 2–4% of plasmacytoid neoplasms whose most relevant representative is the multiple myeloma, the latter representing up to 1% of all general malignancies. Approximately 80–90% of EMP cases involve craniocervical structures (upper aerodigestive tract; larynx; nasopharynx; tonsilla; nasal and paranasal cavities), but the number of cases does not reach 1% of all neoplastic head and neck lesions. Other sites such as gastrointestinal and urogenital tracts, central nervous system, thyroid, parathyroid glands, salivary glands, lymph nodes, skin, lungs, and breasts are uncommon. Lymph node involvement in pulmonary hila is extremely rare, with rates as low as less than 2% of cases. Generally, they present as masses with nonspecific soft parts density. Histologically, such tumors do not originate directly from the bone marrow and cannot be distinguished from multiple myelomas. Also the differentiation from plasmacytoid cell granulomas and other inflammatory reactions is difficult, essentially requiring immunophenotyping. The diagnosis of EMP is made after rigorous investigation to rule out the presence of multiple myeloma, highlighting the histological confirmation by means of immunohistochemical analysis, biopsy/bone marrow puncture showing < 5% of plasmacytoid atypia; to rule out the presence of osteolytic lesions, serum and urinary protein dosage and electrophoresis (to rule out the presence of M and Bence-Jones proteins, respectively); and non-existence of anemia. EMP may be the initial manifestation of multiple myeloma, with progression in about 30% of cases. Lenara Renó Arbex Coelho, Gabriel Pinheiro Coelho, Rodolfo Mendes Queiroz, Marcus Vinicius Nascimento Valentin

Generally, they present as masses with nonspecific soft parts density (3) . Histologically, such tumors do not originate directly from the bone marrow and cannot be distinguished from multiple myelomas. Also the differentiation from plasmacytoid cell granulomas and other inflammatory reactions is difficult, essentially requiring immunophenotyping (1,4) .
PET/CT and brown fat in the evaluation of treatment response in Hodgkin lymphoma PET/CT e gordura marrom na avaliação da resposta terapêutica no linfoma de Hodgkin Dear Editor, A female, 15-year-old patient presented with insidious onset of weight loss and low fever. Hodgkin's lymphoma was diagnosed after biopsy of a palpable enlarged lymph node. 18 F-FDG PET/ CT was performed during the initial staging, demonstrating hy-permetabolic mediastinal, axillary and cervical lymph node enlargement ( Figure 1). The findings were interpreted as lymphoma in activity in the mentioned sites. At basal PET/CT study, one could not observe metabolic activity in brown fat. Chemotherapy was initiated with adriblastine, bleomycine, vinblastine and dacarbazine at days D1 and D15 for every 28-day cycles.
Six chemotherapy cycles were uneventfully performed. A new FDG PET/CT performed after about three months to evaluate the therapeutic response demonstrated complete regression of all the lesions interpreted as lymphoma in activity at the first study. Also, the onset of activity was observed in fat tissue with typical brown fat distribution (at the neck base and shoulders - Figure 2).
Brown fat is an adipose tissue specialized in the generation of heat by means of glucose metabolization (differently from the white fat whose function is just storing energy under the form of lipids) (1,2) .
As compared with white fat, brown fat has abundant vascularization and innervation by the sympathetic nervous system. Many times, the metabolic activity in the brown fat may obscure intermingled hypermetabolic lesions (metastatic lymph nodes, for example) (1,2) .
The onset of activity in brown fat with disappearance of lesions suspicious for active lymphoma after chemotherapy completion in children and adolescents is described in the literature and is related to a complete therapeutic response in the lymphoma (3,4) . Such an inverse relationship between the absence of tumor and presence of brown adipose tissue has been observed in both female and male patients regardless their body mass index and temperature (3,4) . The possible mechanisms for brown fat suppression by the lymphoma still remain unknown. However, patients with malignant lymphomas present with high levels of tumor necrosis factor alpha, an important cytokine capable of inducing a great number of biological effects in multiple systems, including apoptotic degeneration of brown adipocytes (1)(2)(3)(4) .
PET/CT using FDG has been widely adopted as the main imaging modality in the evaluation of lymphomas (5,6) . The identification of brown adipose tissue in humans by PET/CT has revived the interest in the function and relevance of those cells, since there was a concept that they were seen only in neonates, and currently they are identified by PET/CT also in children and young adults (7,8) . The knowledge that the brown adipose tissue is a predictor of disease state contributes to a correct analysis of images from children and adolescents with lymphoma, being useful in the follow-up and clinical therapeutics of those patients.