The aim of this study was to assess sensitivity and responsiveness of power Doppler ultrasound(PDUS) in detecting enthesitis for ankylosing spondylitis(AS) patients compared to clinical examinations.Twenty AS patients initiating etanerceptunderwent clinical and PDUS examinations of six bilateral entheseal sites at baseline and after 1,2 and 3 months of treatment.Clinical and PDUS examinations identified at least one entheseal lesion in nine(45%)and 19(95%) patients,respectively.Furthermore,of 240 entheseal sites examined in these 20 patients,PDUS detected 123 entheseal lesions(51.3%of sites),compared with only 47 entheseal lesions(19.6%) detected by clinical examination(P<0.05).The entheseal lesions found on PDUS were most commonly identified by calcification(33.3%),tendon edema(29.2%),abnormal blood flow(25.8%),a thickened tendon(22.1%),cortical irregularity(12.9%),bony erosions(9.6%) and bursitis at the tendon insertion to the bone cortex(7.1%).Improvements in clinical symptoms and laboratory parameters,and significant decreases in PDUS scores were observed following treatment with etanercept.Improvements in PDUS scores continued during follow-up in patients who entered remission following treatment.In conclusion,PDUS improves detection of structural and inflammatory abnormalities of the enthesis in AS compared to physical examination.In addition,PDUS may be useful inascertaining medications. The aim of this study was to assess sensitivity and responsiveness of power Doppler ultrasound (PDUS) in detecting enthesitis for ankylosing spondylitis (AS) patients compared to clinical examinations. Twenty AS patients initiating etanercept underwent clinical and PDUS examinations of six bilateral enthese sites at baseline and after 1, 2 and 3 months of treatment. Clinical and PDUS examinations identified at least one entheal lesion in nine (45%) and 19 (95%) patients, respectively. Fultrthermore, of 240 entheseal sites examined in these 20 patients, PDUS detected 123 entheseal lesions (51.3% of sites), compared with only 47 entheseal lesions (19.6%) detected by clinical examination (P <0.05) .The entheseal lesions found on PDUS were most commonly identified by calcification (33.3%), tendon edema 29.2%), abnormal blood flow (25.8%), a thickened tendon (22.1%), cortical irregularity (12.9%), bony erosions (9.6%) and bursitis at the tendon insertion to the bone cortex clinical symptoms and l The aboratory parameters, and significant decrease in PDUS scores were observed following treatment with etanercept. MPUSses in PDUS scores continued during-up in patients who entered remission following treatment.In conclusion, PDUS improves detection of structural and inflammatory abnormalities of the enthesis in AS compared to physical examination. In addition, PDUS may be useful in determining the medications.