The role of active brown adipose tissue in patients with pheochromocytoma or paraganglioma (PPGL).

Objectives: Metabolically-active brown adipose tissue (aBAT) is a common finding on ¹⁸FDG-PET imaging in patients with pheochromocytoma or paraganglioma (PPGL). In addition to its clinical significance, we aimed to explore the prevalence of this finding on FDG-PET imaging in patients with PPGL.

Methods: We conducted a systematic review and meta-analysis of prospective and retrospective studies. Publications were identified through searches in MEDLINE/PubMed, Embase, and SCOPUS from inception until 2022-11-26, with an update check performed on 2024-05-02. Eligible studies included patients with PPGL who had completed FDG-PET imaging. Data on catecholamine levels stratified by the presence of aBAT was extracted and pooled using the random-effects model with the inverse variance method. For the quantitative synthesis, we used standardized mean differences (SMD) and meta-analysis of proportions. A risk of bias assessment was performed using the QUIPS tool.

Results: Our search yielded 6 studies suitable for inclusion. Pooled data showed a statistically significant positive difference in isolated demethylated catecholamine levels in aBAT positive groups compared to aBAT negative. No significant differences were found in multiple domains, including tumor size, tumor burden, germline mutations, or location. The proportion of patients with PPGL who present with aBAT stands at approximately 25%.

Conclusions: The demethylated metabolite levels could have potential use in predicting the presence of active brown adipose tissue in patients with PPGL. There is no convincing evidence of increased aBAT prevalence in patients with PPGL and germline mutations. There was, however, evidence suggesting that the presence of aBAT may confer poorer outcomes and decreased life expectancy.