¹⁸F-FDG PET/CT in Takayasu Arteritis - Active or Inactive?

Objectives: Takayasu arteritis (TA) is a rare, inflammatory granulomatous disease involving large-vessels, such as aorta and its branches. Based on angiography, TA is divided into six types which provides an overview of the disease severity/ extent. However, angiography and CT imaging assess vascular thickening and luminal stenosis which does not provide information about disease activity. Clinical assessment and biochemical investigations (ESR, CRP) are used as indirect markers for disease activity. ¹⁸F-FDG accumulation can potentially detect sites with active disease, especially in the setting of multifocal disease where some disease sites may be active and others may be inactive. The present study was aimed to evaluate the role of ¹⁸F-FDG PET/CT in patients with TA.

Methods: Records of 46 patients (31 women, 15 men; mean age: 30.3 ± 11.9 years) with TA who underwent ¹⁸F-FDG PET/CT from January, 2018 to July, 2019 were retrospectively reviewed. The PET/CT study was interpreted independently by two experienced Nuclear Medicine physicians and any pathologic uptake in the vessel wall (more than the blood-pool activity) was assessed semi-quantitatively using standardized uptake maximum (SUVmax) values along with measurement of wall thickening. Correlation of PET/CT findings was done with biochemical investigations (ESR/CRP), clinical findings and angiography findings wherever available.

Results: 40 patients had undergone ¹⁸F-FDG PET/CT for baseline workup or recurrence evaluation while 6 were for response to therapy assessment. PET/CT was positive for active disease in 31/46 patients (67.4%) with mean SUVmax of 5.7 ± 1.5 (values measured from the vessel showing highest activity in each patient) and arterial wall thickening of 4 ± 1.3 mm. The vessel wall thickening measured in patients with inactive disease on PET/CT was 3 ± 1.9 mm, which was not statistically different from the vascular mural thickening in patients with active disease. Differences in ESR and CRP (available in 42/46 patients) values among patients with active disease on PET/CT versus inactive disease were statistically significant. The most common vessel involved in patients with active disease was the descending thoracic aorta (involved in 90%; mean SUVmax 4.6 ± 1.7), followed by the left subclavian artery (involved in 71%; mean SUVmax 4.9 ± 1.3).

Conclusions: Assessment of disease activity in TA is currently based on the NIH criteria (clinical features, ESR, angiography findings, vascular ischaemia). However, conventional imaging is mainly focused on mural thickening, stenoses and other anatomic changes which may not reflect the acute disease state. ¹⁸F-FDG accumulation at vessel wall can provide a more sensitive assessment of the disease activity. In the present study, findings on PET/CT correlated well with ESR/ CRP values and could identify active disease status in patients. Being a non-invasive modality, ¹⁸F-FDG PET/CT can provide valuable assessment of disease status, recurrence evaluation as well as in judgment of response to treatment.