# Achilles Tendon Xanthoma Inflammation Revealed by FDG-PET/CT in Familial Hypercholesterolemia: Insights From a 2-Generation Case Series

## TL;DR

This paper shows how FDG-PET/CT can reveal inflammation in Achilles tendon xanthomas in familial hypercholesterolemia, highlighting differences in metabolic activity based on treatment duration.

## Contribution

The study introduces FDG-PET/CT as a tool to assess metabolic activity in FH-related xanthomas and reveals phenotypic heterogeneity in two generations.

## Key findings

- FDG-PET/CT showed metabolically active inflammation in Achilles tendon xanthomas after short-term lipid-lowering therapy.
- Long-term lipid-lowering therapy was associated with reduced FDG uptake in Achilles tendon xanthomas.
- Phenotypic differences suggest roles of disease stage and treatment duration in xanthoma inflammation.

## Abstract

Achilles tendon xanthomas are hallmark lesions of familial hypercholesterolemia (FH), but their metabolic activity remains poorly characterized.

We report a 2-generation case series illustrating phenotypic heterogeneity in tendon xanthomas despite shared FH-associated variants. In case 1, a 35-year-old man with bilateral Achilles tendon thickening was diagnosed with FH. After 12 months of lipid-lowering therapy, intense 18F-fluorodeoxyglucose (FDG) uptake on positron emission tomography/computed tomography (PET/CT) indicated metabolically active inflammation. In case 2, the man's 71-year-old father, who had been receiving long-term statins (>10 years), ezetimibe (>1 year), and recent proprotein convertase subtilisin/kexin type 9 inhibitor (1 month), had Achilles tendon thickening but no FDG uptake despite age and coronary artery disease history.

These findings show that xanthomas exhibit persistent metabolic activity despite short-term lipid lowering, whereas prolonged therapy may attenuate inflammation. Phenotypic differences underscore roles of disease stage, cumulative lipid exposure, and treatment duration. FDG-PET/CT provides metabolic information for risk assessment and therapeutic monitoring.