Can Achilles Tendon Assessment of Adult Familial Hypercholesterolemia be Reflected as a Risk Factor for Arteriosclerosis?

See article vol. 29: 1603-1612

Familial hypercholesterolemia (FH) is a hereditary metabolic disorder characterized by low-density lipoprotein (LDL)-hypercholesterolemia, Achilles tendon thickening, and premature coronary artery disease associated with LDL receptors and related genetic mutations ¹⁾ . In adult FH, the initial onset age of coronary artery disease is 15 to 20 years earlier than that in the general population, and FH accounts for about 10% of acute coronary syndrome patients ^{2 - 4)} . In Japan, FH is one of the major underlying conditions in cardiovascular disease. Thus, observation for thickening of the Achilles tendon is essential for confirming the diagnosis of adult FH. Conventionally, xeroradiography has been used in evaluating the degree of thickening, and a maximum tendon diameter of ≥ 9 mm is defined as significant thickening according to FH diagnostic criteria ( Fig.1A ) ^{5 , 6)} . However, the Achilles tendon attachment point is a common site of torsion, and the border between the skin and Achilles tendon is indistinguishable on X-ray images. This could lead to overestimation of the amount of actual thickening. Tada et al. reported that the cutoff values were 7.6 mm for men and 7.0 mm for women in the Achilles tendon X-ray examination in genetically diagnosed FH patients in Japanese ⁷⁾ . Another source of discrepancy is the fact that, while Achilles tendon width is gauged by palpation, thickness in the longitudinal direction is evaluated using X-rays. Given these issues, evaluation of Achilles tendon thickness by ultrasound has now attracted much attention ⁸⁾ . In 2018, the Japan Society of Ultrasonics in Medicine and the Japan Atherosclerosis Society jointly announced a standard evaluation method for measuring the thickness of the Achilles tendon by ultrasonography, for adult FH screening. With this method, the diagnostic criterion for Achilles tendon thickness was indicated as ≥ 6.0 mm for men and ≥ 5.5 mm for women ( Fig.1B ) ⁹⁾ .

Fig.1. Left Achilles tendon with familial hypercholesterolemia (18-year-old man).

A: Achilles X-ray. Achilles tendon thickness is 9mm.

B: Ultrasonography. Achilles tendon thickness is 6mm.

Additionally, ultrasonography usage has made it possible to observe Achilles tendon properties that have, thus far, been insufficiently evaluated ^{10 , 11)} . Specifically, the presence of high brightness areas associated with acoustic shadows, that are suggestive of calcification in the Achilles tendon, as well as uneven, irregular hypoechoic regions that are thought to be xanthomas, can be observed with this method ¹²⁾ . As with Achilles tendon thickening, the presence of these findings might be evidence of suspected adult FH, although, so far, they are used for reference only.

Recently, it was demonstrated that the Achilles tendon in adult FH is softer than that in non-FH patients, and that evaluation of the softness using ultrasound improves the accuracy of FH diagnosis ^{13 , 14)} . In FH, there is age-related fat deposition on the Achilles tendon, which is thought to result in the thickening and softening of the tendon. However, it is unclear whether this correlates with atherosclerosis in peripheral arteries. This article, by comparing the Achilles tendon thickness and elasticity index, and intima-media thickness of the common carotid artery, discusses whether lipid deposition in the Achilles tendon in FH patients can be used in diagnosing the severity of arteriosclerosis ¹⁵⁾ . Although, it does not promise to cover all indices of arteriosclerosis that can be evaluated with carotid artery ultrasonography, such as the presence or absence of carotid artery plaques and the existence of calcification lesions, their presence in patients with FH are thought to be important findings that might correlate with the occurrence of arteriosclerosis in peripheral arteries. In future, we look forward to elucidation of whether various factors, such as longitudinal changes, plaque properties, and the existence of calcified lesions, are related to thickness and properties of Achilles tendon.

Conflicts of Interest

None.