EURURO Vol. 73 No. 1

Research Letters

[

F]-Fluorodeoxyglucose Positron Emission Tomography and

Response to Therapy in Idiopathic Retroperitoneal Fibrosis

Eugenia

[1_TD$DIFF]

Accorsi

[2_TD$DIFF]

Buttini, Federica Maritati, Augusto Vaglio

[

F]-Fluorodeoxyglucose positron emission tomography

(

F-FDG-PET) has become valuable in diagnosing and

monitoring idiopathic retroperitoneal fibrosis (RPF). In a

cohort of 49 patients with idiopathic RPF, Fernando and

colleagues

[1]

investigated whether

F-FDG-PET predicts

response to glucocorticoid therapy. Response (defined as

RPF shrinkage, a reduction in FDG uptake, or normalization

of inflammatory markers) was achieved in 9/11 patients

(82%) with high-grade positive PET, 3/24 patients (12%) with

low-grade positive PET, and 0/14 patients with negative PET.

On the basis of these findings, glucocorticoids should not be

given to patients with metabolically inactive RPF, and

responses are expected only in those with very active

disease.

These results do not appear to reflect our practice, so we

reviewed our experience with

F-FDG-PET in idiopathic

RPF. We studied all idiopathic RPF patients seen at our

centre between 2007 and 2016 who: (1) underwent

F-FDG-PET at diagnosis or relapse; (2) received predni-

sone (initial dose 0.75

–

1 mg/kg/d) and/or other immuno-

suppressants (eg, methotrexate, mycophenolatemofetil) for

–

9 mo; (3) had computed tomography (CT) or magnetic

resonance imaging (MRI) scans before and after treatment;

and (4) had follow-up

12 mo.

F-FDG-PET was repeated at

the end of the treatment in patients with a positive baseline

study.

F-FDG uptake was graded as follows: 0 = no uptake;

1 = lower than liver uptake; 2 = similar to liver uptake; and

3 = higher than liver uptake

[2] .

Remission was defined as

the disappearance of clinical manifestations, resolution of

ureteral obstruction, and normalization of acute-phase

reactants

[3] .

We also assessed the reduction in RPF

maximal thickness on CT/MRI and metabolic responses

on FDG-PET, the latter according to PERCIST criteria

[4]

Sixty-eight patients were studied (Supplementary Ta-

ble 1). At baseline, six patients (8.8%) had a negative FDG-

PET, while four (5.9%) had grade 1, 20 (29.4%) had grade 2,

and 38 (55.9%) had grade 3 FDG uptake. A reduction in RPF

thickness was detectable in some patients with grade

0 uptake, although it seemed to be lower than in the other

groups

( Fig. 1

A). RPF shrinkage was comparable in patients

with grade 1, 2, and 3 uptake. A similar pattern was

observed for the erythrocyte sedimentation rate

( Fig. 1

B).

Metabolic response rates were comparable for patients with

grade 1

–

3 uptake

( Fig. 1 C

). Finally, remission was achieved

in 33% of patients with grade 0 uptake, although this rate

was lower than that observed in patients with grade 2

(

= 0.02) or grade 3 uptake (

= 0.01). Remission rates were

similar in patients with grade 1

–

3 uptake

( Fig. 1 D

Thus, negative

F-FDG-PET does not necessarily predict

refractoriness to treatment, although response rates are

lower in patients with negative than in those with positive

F-FDG-PET. This is in agreement with a previous study

reporting that absence of

F-FDG uptake does not preclude

an RPF response

[5] .

In addition, we observed that different

grades of PET positivity are not associated with different

response rates. Our work has limitations, namely its

retrospective nature, the small size of each uptake grade

group (particularly grades 0 and 1), and the use of criteria

(eg, PERCIST) designed for evaluation of solid tumors. It

must also be acknowledged that it is difficult to compare

our study to that by Fernando et al because of the different

patient sources (urological vs clinical), treatments, and PET

E U R O P E A N U R O L O GY 7 3 ( 2 0 18 ) 14 5 – 14 8

ava ilable at

www.sciencedirect.com

journal homepage:

www.eu ropeanurology.com