Background/Purpose:

Fluorine-18-fluorodeoxyglucose (FDG) PET/CT is increasingly used to diagnose large vessel GCA (LV-GCA), but has previously been considered unable to reveal inflammation in temporal arteries due to limited spatial resolution. However, the arteritic pattern in GCA is heterogeneous and additionally may not always uniformly involve the entire vessel, rendering interpretation of the PET images difficult. An increased FDG uptake in branches of the external carotic artery, i.e. the temporal (TA) and maxillary arteries (MA), may therefore add to diagnostic specificity.

Methods:

21 patients fulfilling the ACR criteria of GCA were identified from a LV-GCA cohort (table 1). Laboratory tests, temporal artery ultrasound (US) and FDG PET/CT (Siemens Biograph 64) were performed prior to treatment.

An experienced nuclear medicine physician performed blinded assessment of FDG uptake in TA and MA. FDG uptake was visually scored on a 4-point scale (a.m. Meller¹: 1; ≤ blood pool, 2; > blood pool, ≤ liver, 3; ≥ liver, 4; ≥ 2xliver), where score ≥2 was considered indicative of inflammation. In addition, mean and max standardized uptake values (SUV_mean, SUV_max; 20 hottest interconnected pixels) and target to background ratio (TBR=SUV_max(artery)/SUV_mean(venousblood)) were recorded for each vessel based on volumes of interest drawn on the PET images.

Correlations were calculated using Spearman’s test. Mann–Whitney U test or Student t test, when applicable, were used for quantitative data. Associations between two categorical variables were evaluated using Fisher’s exact test.

Results:

FDG uptake in cranial arteries was detectable in 20/21 patients; 12/21 TA and 20/21 MA. In 11 patients, at least one of the arteries was categorized with a Meller score≥2 indicating significant inflammation. SUVs and TBRs are shown in table 1. SUVs and TBR correlated with Meller scores.

In the 3 patients with negative TA US (n=2 biopsy positive) and in the 2 patients with negative TA biopsies (n=1 US positive), FDG uptake in TA and MA was either not detectable or with a Meller score of 1. Meller score in the TA correlated with the degree of inflammation (none, <transmural, transmural) in the TA biopsy (rho=0.64, p<0.01). Patients with a TA or MA Meller score≥2 were more likely to have severe cranial symptoms (p=0.02), jaw claudication (p<0.02), had a shorter disease duration prior to diagnosis (median 8 vs 17 weeks, p<0.02) and were younger (median 65 vs 69 years, p<0.01) than patients with Meller score<2. However, they did not differ in gender or CRP at time of diagnosis.

Conclusion:

Increased FDG uptake in the cranial arteries of GCA patients is frequent, correlated to histological inflammation and subjective symptoms and detectable by normal PET/CT systems. It may add to the diagnostic accuracy of 18F-FDG PET/CT in GCA and should not be overlooked by reading physicians.

Table 1

References

1. Stellingwerff MD et al. Medicine 2015