18. An unusual PET project: large vessel vasculitis presenting as lower limb claudication in the absence of aortitis
Authors: Morton Neil , Man Yik Long , D’Cruz David 
Published: September 2019

Abstract

Introduction
Rheumatologists are increasingly aware of extracranial giant cell arteritis (GCA), namely large vessel vasculitis (LVV) involving the aorta and its branches. It is uncommon for patients to present with claudication as their initial complaint. We present an unusual case of femoral arteritis presenting with lower limb claudication. PET-CT demonstrated increased uptake bilaterally in the femoral arteries with typical hypoechoic haloes on Doppler ultrasound. There was no evidence of aortitis. We also illustrate the diagnostic challenge differentiating between vasculitis and atherosclerosis on PET-CT and how steroid-therapy reduces the sensitivity PET imaging.

Case description
A 57-year-old lady with known hypertension presented to her local hospital with a 3-year history of worsening claudication in her lower limbs. Her exercise tolerance was limited to 50 metres over the past 2 months and she had rest pain. Other symptoms included widespread musculoskeletal pain, chest pain, headaches and jaw pain on mastication. Lower limb Doppler ultrasound demonstrated significant stenosis of the distal femoral arteries bilaterally with hypoechoic haloes typical for vasculitis. Immunology tests were all negative but inflammatory markers were raised (ESR 43 mm/h, CRP 14 mg/L). In view of the Doppler findings and GCA symptoms she was started on prednisolone 60mg. The prednisolone was held 2 days before a PET-CT which demonstrated mild uptake in both femoral arteries with no evidence of aortitis. Her CT angiogram showed significant diffuse atheromatous disease in the superficial femoral and popliteal arteries bilaterally. In view of this, the PET-CT uptake was thought to be in keeping with atherosclerosis rather than vasculitis. Her prednisolone was therefore stopped and she was transferred to a tertiary vascular centre for further management.
The vascular team at our hospital were still concerned about the possibility of vasculitis and a second rheumatology opinion was sought. Her inflammatory markers continued to rise (ESR 76 mm/h, CRP 29 mg/L). It was felt that the PET-CT results may have been affected by high-dose prednisolone which was temporarily held. The PET-CT was therefore repeated having been off steroids for 4 weeks. This demonstrated increased uptake in the superficial femoral and profunda arteries when compared to her previous scan. All her images were reviewed and the diagnosis was felt to be in keeping with LVV. Furthermore, she had a good clinical response to 40mg prednisolone and methotrexate was subsequently added.

Discussion
Classical GCA typically presents with cranial symptoms. Extracranial symptoms such claudication can occur although only 4% of patients fall into this category. In our patient, femoral arteritis presented with lower limb claudication. Peripheral limb ischaemia and/or aorta involvement is associated with a slightly younger demographic of LVV (<60 years).
Initially, there was diagnostic uncertainty given her raised inflammatory markers and hypoechoic femoral artery haloes on Doppler ultrasound, yet diffuse atherosclerosis on the CT angiogram. Hypoechoic haloes and multiple short segment occlusions are more typically seen in vasculitis rather than atherosclerotic disease. Accelerated atherosclerosis is common in primary vasculitides. Despite establishing the diagnosis of LVV by ultrasound in this case, the sensitivity for this in the common femoral artery is < 17%, and PET-CT is preferred. EULAR recommendations for LVV diagnosis include ultrasound and PET-CT. PET-CT was performed twice in this patient because the initial scan was performed following temporary cessation of high-dose steroids, which can decrease the sensitivity of PET-CT. The first PET-CT showed only mild uptake in the femoral arteries which could be consistent with atherosclerosis. Interestingly, PET-CT has been used to identify plaques vulnerable to rupture bed on FDG-avidity. Recent studies have utilised PET-CT to quantify the burden of atherosclerotic disease to help risk stratify patients accurately. This potential diagnostic ambiguity between vasculitis and atherosclerosis on PET-CT reinforces the importance of remaining off steroids around the time of PET imaging where possible.

Key learning points
This case sheds light on LVV through several interesting perspectives. Firstly, it is unusual for LVV to present with claudication in the lower limbs in the absence of aortitis, demonstrating the variety of ways in which the same pathophysiological mechanism can present clinically. We also highlight the initial diagnostic challenge, as mild uptake in the femoral arteries on PET-CT can be consistent with atherosclerosis. However, with typical findings of hypoechoic haloes on Doppler ultrasound and raised inflammatory markers, clinically this was in keeping with LVV. Interestingly, a repeat PET-CT off steroids demonstrated increased FDG-avidity in the affected areas. This is important as even holding steroids for 2 days before a PET-CT affected the results of the study. This case adds to the growing number of atypical extracranial presentations of LVV and provides useful insight for future possible cases.

Conflict of interest
The authors declare no conflicts of interest.