Extraocular muscles have fundamentally distinct properties that make them selectively vulnerable to certain disorders

Department of Neurology, The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK.
Neuromuscular Disorders (Impact Factor: 2.64). 02/2005; 15(1):17-23. DOI: 10.1016/j.nmd.2004.10.002
Source: PubMed


While skeletal muscles generally perform specific limited roles, extraocular muscles (EOMs) have to be responsive over a wider dynamic range. As a result, EOMs have fundamentally distinct structural, functional, biochemical and immunological properties compared to other skeletal muscles. While these properties enable high fatigue resistance and the rapid and precise control of extraocular motility, they might also explain why EOMs are selectively involved in certain disorders, such as chronic progressive external ophthalmoplegia (CPEO), myasthenia gravis and Graves' ophthalmopathy. This review first gives an overview of the novel myofibre classification in EOMs and then focuses on those properties that might explain why ophthalmoplegia should be so prominent in these disorders.

Download full-text


Available from: Cynthia Yu-Wai-Man, Aug 23, 2014
  • Source
    • "EOMs have a unique myofibrillar protein isoform composition reflecting their structural and functional properties [8]. Compared with skeletal muscle, EOMs have smaller motor unit sizes, higher motor neuron discharge rates, higher blood flow with higher mitochondrial volume fractions which can suggest that the energy requests and susceptibility to mitochondrial dysfunction are higher as compared with skeletal muscle [2,9]. Due to the high blood flow and vascularisation, inflammatory blood cells can access more easily this specialized body compartment [2, 10]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the case of a 43 year old man who presented recurrent left abducens palsy. His medical history included arterial hypertension, ischemic cardiomiopathy, dyslipidemia, rhinitis, maxillary sinusitis. Physical examination revealed a overweight patient, horizontal gaze diplopia, left nerve VI paresis, mild left retro-orbital pain. The orbital MRI also didn't offer new information: mild external edema on the left eye, with normal tendon aspect, no thickening or enhancement of the muscle belly and also normal aspect of the bony orbit. Recurrent palsy of EOMs can be caused in rare cases by ocular myositis.
    Full-text · Article · May 2014
  • Source
    • "The extraocular muscles (EOM) have a wide dynamic range making their structure, biochemistry and immunology distinct from skeletal muscle. This has been suggested as a reason for their selective involvement in certain mitochondrial disorders [75]. A study in 2006 looked at the specific findings in the EOM in patients with CPEO using high-resolution orbital MRI. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Mitochondrial DNA mutations are an important cause of neurological disease. The clinical presentation is very varied in terms of age of onset and different neurological signs and symptoms. The clinical course varies considerably but in many patients there is a progressive decline, and in some evidence of marked neurodegeneration. Our understanding of the mechanisms involved is limited due in part to limited availability of animal models of disease. However, studies on human post-mortem brains, combined with clinical and radiological studies, are giving important insights into specific neuronal involvement.
    Full-text · Article · Aug 2009 · Biochimica et Biophysica Acta
  • Source
    • "Many skeletal muscle diseases (including Duchenne, Becker, limb-girdle and most congenital muscular dystrophies and congenital myopathies) do not affect the extraocular muscles (EOMs), while other diseases (e.g. mitochondrial disorders and myasthenia gravis) do affect the extraocular muscles [1] [2] [3]. Mutations in the skeletal muscle a-actin gene (ACTA1) have been shown to cause several congenital myopathies (reviewed in [4]). "
    [Show abstract] [Hide abstract]
    ABSTRACT: As with many skeletal muscle diseases, the extraocular muscles (EOMs) are spared in skeletal muscle alpha-actin diseases, with no ophthalmoplegia even in severely affected patients. We hypothesised that the extraocular muscles sparing in these patients was due to significant expression of cardiac alpha-actin, the alpha-actin isoform expressed in heart and foetal skeletal muscle. We have shown by immunochemistry, Western blotting and a novel MRM-mass spectrometry technique, comparable levels of cardiac alpha-actin in the extraocular muscles of human, pig and sheep to those in the heart. The sparing of extraocular muscles in skeletal muscle alpha-actin disease is thus probably due to greater levels of cardiac alpha-actin, than the negligible amounts in skeletal muscles, diluting out the effects of the mutant skeletal muscle alpha-actin.
    Full-text · Article · Nov 2008 · Neuromuscular Disorders
Show more