Unmasking Cerebrotendinous Xanthomatosis

A 56-year-old woman with consanguineous parents presented with progressive neurologic deterioration over 6 years.At age 53, she developed cognitive decline and gait instability, progressing to cerebellar ataxic gait and moderate dementia (MMSE score 18/30).Neurologic examination revealed cerebellar dysfunction including saccadic eye movements, scanning speech, dysdiadochokinesia, and limb ataxia with decomposition and dysmetria.Upper motor neuron signs included spastic paraparesis, hyperreflexia, and Babinski signs.Key diagnostic clues included premature cataracts (at age 40), a palpable left patellar mass (Figure A) with bilateral Achilles tendon thickening, and fluorodeoxyglucose positron emission tomography-PET for malignancy workup demonstrating uptake in these tendons-findings distinguishing multitendinous xanthomas from unilateral malignancies (Figure B).Brain MRI revealed characteristic bilateral dentate nuclei hyperintensities on fluid-attenuated inversion recovery (Figure C)-a hallmark finding neurologists should recognize.Elevated serum cholestanol (17.4 g/mL; reference 4.5) and homozygous CYP27A1 c.1421G > A (p.R474Q) variant confirmed cerebrotendinous xanthomatosis (CTX). 1The triad of juvenile cataracts, ataxia, and tendon xanthomas should prompt CTX consideration because early chenodeoxycholic acid therapy prevents irreversible neurologic damage.