MAGNETIC RESONANCE Extra-ocular muscle MRI in genetically-defined mitochondrial disease Robert D. S. Pitceathly 1 & Jasper M. Morrow 1 & Christopher D. J. Sinclair 1,2 & Cathy Woodward 3 & Mary G. Sweeney 3 & Shamima Rahman 1,4 & Gordon T. Plant 5,6 & Nadeem Ali 5,6 & Fion Bremner 5 & Indran Davagnanam 7 & Tarek A. Yousry 1,2 & Michael G. Hanna 1 & John S. Thornton 1,2 Received: 7 January 2015 /Revised: 28 March 2015 /Accepted: 14 April 2015 # The Author(s) 2015. This article is published with open access at Springerlink.com Abstract Objectives Conventional and quantitative MRI was per- formed in patients with chronic progressive external ophthalmoplegia (CPEO), a common manifestation of mito- chondrial disease, to characterise MRI findings in the extra- ocular muscles (EOMs) and investigate whether quantitative MRI provides clinically relevant measures of disease. Methods Patients with CPEO due to single mitochondrial DNA deletions were compared with controls. Range of eye movement (ROEM) measurements, peri-orbital 3 T MRI T1- weighted (T1w) and short-tau-inversion-recovery (STIR) im- ages, and T2 relaxation time maps were obtained. Blinded observers graded muscle atrophy and T1w/STIR hyperintensity. Cross-sectional areas and EOM mean T2s were recorded and correlated with clinical parameters. Results Nine patients and nine healthy controls were exam- ined. Patients had reduced ROEM (patients 13.3°, controls 49.3°, p<0.001), greater mean atrophy score and increased T1w hyperintensities. EOM mean cross-sectional area was 43 % of controls and mean T2s were prolonged (patients 75.6±7.0 ms, controls 55.2±4.1 ms, p<0.001). ROEM corre- lated negatively with EOM T2 (rho= -0.89, p<0.01), whilst cross-sectional area failed to correlate with any clinical measures. Conclusions MRI demonstrates EOM atrophy, characteristic signal changes and prolonged T2 in CPEO. Correlation be- tween elevated EOM T2 and ROEM impairment represents a potential measure of disease severity that warrants further evaluation. Key Points • Chronic progressive external ophthalmoplegia is a common clinical manifestation of mitochondrial disease. • Existing extra-ocular muscle MRI data in CPEO reports variable radiological findings. • MRI confirmed EOM atrophy and characteristic signal changes in CPEO. • EOM T2 was significantly elevated in CPEO and correlated negatively with ocular movements. • EOM T2 represents a potential quantitative measure of dis- ease severity in CPEO. Keywords Magnetic resonance imaging . Mitochondrial diseases . Mitochondrial DNA . Chronic progressive external ophthalmoplegia . Kearns-Sayre syndrome Abbreviations CPEO Chronic progressive external ophthalmoplegia EOM(s) Extra-ocular muscle(s) IO Inferior oblique * Robert D. S. Pitceathly r.pitceathly@ucl.ac.uk 1 MRC Centre for Neuromuscular Diseases, UCL Institute of Neurology and National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK 2 Neuroradiological Academic Unit, Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, London WC1N 3BG, UK 3 Neurogenetics Unit, National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK 4 Mitochondrial Research Group, Clinical and Molecular Genetics Unit, UCL Institute of Child Health, London WC1N 1EH, UK 5 Department of Neuro-ophthalmology, National Hospital for Neurology and Neurosurgery, London WC1N 3BG, UK 6 Department of Neuro-ophthalmology, Moorfields Eye Hospital, London EC1V 2PD, UK 7 The Lysholm Department of Neuroradiology, National Hospital for Neurology and Neurosurgery, London WC1N 3BG, UK Eur Radiol DOI 10.1007/s00330-015-3801-5