The use of Achilles tendon sonography to distinguish familial hypercholesterolemia from other genetic dyslipidemias

Objective - Achilles tendon (AT) xanthomas, specific for familial hypercholesterolemia (FH), may be clinically undetectable. We assessed the usefulness of AT sonography in the diagnosis of FH. Methods and Results - Sonographic AT characteristics were evaluated in 127 subjects with FH ( 81 genetically ascertained), 84 familial combined hyperlipidemia, 79 polygenic hypercholesterolemia, and 88 normolipidemic controls. Abnormal echostructure (sonographic xanthoma) was noted only in FH. AT thickness was higher ( P < 0.001) in FH men and women compared with all of the other groups and, in FH mutation carriers but not in others, correlated positively with low-density lipoprotein cholesterol ( r = 0.345; P < 0.001) and negatively with high-density lipoprotein cholesterol ( r = - 0.265, P = 0.015). Thickness thresholds for the diagnosis of FH with specificity > 80%, as were derived from receiver operating curves, were 5.3 and 5.7 mm in men < and > 45 years, and 4.8 and 4.9 mm in women < and > 50 years, respectively. In FH mutation carriers, sonographic findings increased the clinical diagnosis of xanthomas from 35 (43%) to 55 (68%). Using thresholds in validation sets of 70 genetically identified FH and 54 dyslipidemic non-FH correctly classified 80% and 88%, respectively. Conclusion - Sonographic AT characteristics are normal in non-FH dyslipidemias. Identification of suspected FH by ultrasound using sex- and age-specific AT thickness thresholds is recommended.