P190 Protocolised ultrasonography led pathway has a high sensitivity for diagnosis of primary large vessel vasculitis

Abstract Background/Aims Ultrasonography (US) for diagnosis of large vessel vasculitis (LVV) is a recommended first line diagnostic procedure. Our county has an annual incidence of 57.5/million for primary LVV (giant cell arteritis (GCA) 48.3/million; Takayasu 2.5/million; unclassified LVV 6.4/million). Our protocolised fast-track US pathway has reduced visual loss from 18.7% to 11.5%. We present the results of our first 1000 unique referrals. Methods Unique requests for US from January 2017 were analysed. Protocolised US examination of the arteries includes superficial temporal artery (STA) and its rami, followed by the entire axillary artery, followed by other arteries as necessary. Halo sign in at least two different arteries was needed for diagnosis of LVV. A temporal artery biopsy (TAB) or positron emission tomography (PET) were requested if the US was negative AND CRP was ≥20mg/L (or missing) AND an alternate explanation for the raised CRP was not immediately apparent. For those where a second test was not requested OR if it was negative, prednisolone was tapered rapidly, and a patient-initiated follow-up allowed rapid re-assessment. If referring physician or patient did not want a second test, GCA was diagnosed on clinical grounds alone and the pathway was considered to have failed. Results Median age was 73 (IQR 13); 11/1000 referrals were for people <50 years of age. The median delay for the procedure was 4 (IQR 4) days. Prednisolone had been started a median of 4 (IQR 5) days previously. 279/1000 (28%) US scans demonstrated vasculitis. Pre-steroid CRP was ≥20mg/L in 283 cases and unavailable in 7. An alternate explanation for the raised CRP was found in 102 cases, 181 were referred for a second test, and 7 received a clinical diagnosis of GCA without a second test. The second test was diagnostic in 31/181 (17%) - 24/139 (17%) TAB, 7/42 (17%) PET. 3/150 cases with a negative second test and 4/431 cases with CRP <20mg/L were diagnosed with GCA on patient-initiated follow-up. The delayed diagnosis did not result in visual loss. 202/279 (72%) US positive cases had bilateral STA involvement. The addition of axillary artery imaging picked up a further 53 (19%) cases; 24/279 (9%) cases needed imaging of other arteries. The sensitivity and negative predictive value of the pathway are 96% (310/324) and 98% (683/690) respectively. Conclusion Our protocolised US led pathway for diagnosis of LVV is highly sensitive and allows disease exclusion with high certainty. Routine US of the superficial temporal artery and its rami, and the entire axillary artery provide diagnosis in 91% of cases but ability to scan more arteries improves yield in a further 9% of cases. Composite testing with US plus second test, stratified by CRP levels, can be recommended as a gold standard diagnostic tool for LVV. Disclosure C.B. Mukhtyar: None. G. Ducker: None. C. Beadsmoore: None. K. Sisson: None. C. Jones: None.