Difference between revisions of "Ocular Manifestations of Myotonic Dystrophy"

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Electromyography demonstrating typical myotonic discharges.
  
 
== History  ==
 
== History  ==

Revision as of 22:16, January 2, 2015

Assigned editor:
Review:
Assigned status Update Pending
 by Erin Seefeldt, MD on January 2, 2015.


Myotonic Dystrophy is a multi-system disease, which can initially present with symptoms of ptosis, ophthalmoplegia, extraocular myotonia, and decreased visual acuity. On slit lamp examination of the lens an iridescent, “christmas tree” pattern, cataract is detectable in 100% of patients with myotonic dystrophy by the age of 45. Further genetic testing can be done to confirm the disease. The cataract can be removed to help restore vision, however, cases of recurrent post capsular opacification have been reported, requiring multiple Nd:YAG laser capsulotomies.

Disease Entity

Myotonic Dystrophy is a tri-nucleotide repeat, autosomal dominant disease characterized by an inability to relax (myotonia) and muscle wasting (muscular dystrophy). Two main types of myotonic dystrophy exist, Myotonic Dystrophy 1 and Myotonic Dystrophy2, also known as Proximal Myotonic Myopathy. Myotonic Dystrophy 1 has a greater severity of symptoms, as compared to Mytonic Dystrophy 2, and is the most common adult form of muscular dystrophy affecting nearly 1 in 8,000 people worldwide . In addition to the myotonia and muscular dystrophy, Myotonic Dystrophy 1 is a debilitating multi-system disease having affects on the eye, pulmonary, cardiac, endocrine, and central nervous system. Respiratory failure is the leading cause of death in theses patients, responsible for 30% of mortalities. Cardiac conduction abnormalities are the second leading cause of death at approximately 20% of mortalities . An increase in the PR interval and a widened QRS may be the first asymptomatic signs in these patients, which eventually progress to Supraventricular Tachycardia (SVT), Ventricular Fibrillation, and asystole. A distinctive cataract presents in 100% of patients with either Myotonic Dystrophy, which can aid in the diagnosis of this complex disease.

Disease

Due to its wide range of symptoms, diagnosis of this disease is sometimes difficult and may be prolonged. However, ocular manifestations of the disease may be one of the first presenting symptoms and thus cause a patient to seek care. Symptoms may include ptosis, ophthalmoplegia, epiphora, extraocular myotonia, decreased visual acuity, and or difficulty coping with glare from bright lights.

Significant ptosis may cause visual impairment; however, caution must be taken in performing ptosis surgery if levator function is significantly reduced and/or severe frontalis and orbicularis muscle weakness is present, as this can limit the effectiveness of frontalis sling and increase the risk for exposure keratopathy.

Extraocular mytonia is manifested as slowed and disconjugate saccades. More specifically, the abnormalities consist of a reduction in saccade peak velocity and increased saccade duration primarily if the eye is fixed on an object for a longer period of time (long interstimulus interval) , thus highlighting the phenomenon of myotonia. The finding of ophthalmoplegia consists of limited adduction, labeled as “pseudo-internuclear ophthalmoplegia .” Multiple cases of bilateral adduction restriction have been reported, as well as those with divergent strabismus and convergence paralysis . The abducting eye did not present with nystagmus.

On slit lamp examination, an ophthalmologist or optometrist may see a formation of a cataract with fine dust like opacities on the outer layers of the lens that are highly colored and iridescent, producing a “Christmas Tree” appearance. Other signs may include low intraocular pressure, due to ciliary body detachment , maculopathy and peripheral pigmentary retinopathy . The combination of a cataract and retinal degeneration may lead to low visual acuity in these patients. Cataracts affect all patients with any form of myotonic dystrophy by age 45 and begins to form early in the teenage years; therefore, the presence of such a distinct cataract is an important clue to the diagnosis of the disease. Early onset presentation of a bilateral iridescent cataract, especially at age less than 45 and without pre-existing diabetes, in a patient with a positive family history of myotonic dystrophy should undergo genetic testing to confirm the presence of the disease.

Etiology

In myotonic dystrophy the CTG repeats on Chromosome 19 affect the 3’ untranslated region of the myotonic dystrophy protein kinase gene (DMPK), causing a decreased expression of the protein. Decreased DMPK expression in extraocular muscles, ciliary body, and cellular layers of the retina can account for the symptoms seen in myotonic Dystrophy. Interestingly, very little to no DMPK expression is seen in lens epithelium. The tri-nucleotide repeat expansion decreases the expression of the downstream six5 gene, which has been hypothesized to be the cause of the distinct cataract in mytonic dystrophy.

Risk Factors

Autosomal Dominant

General Pathology

The cataract first begins with iridescently colored fine opacities on the outer layer of the lens (cortical and subcapsular). As the cataract matures, these fine opacities increase and cortical spoking develop making it difficult to distinguish it from a cortical cataract . An increased level of Gamma-Glutamyl Transpeptidase in these patients may be responsible for low levels of lenticular glutathione and thus leading to the cataract formation . The cataract can be removed to help restore vision, but care must be taken in selecting an anesthetic agent in order to reduce the risk of intraoperative and postoperative complications . Some patients with Myotonic Dystrophy may have delayed recovery after an operation with use of certain anesthetic agents. However, traditionally cataract surgery utilizes local anesthesia, which causes no such problems of delayed recovery . Post-operative ocular complications include recurrent post capsular opacification (PCO) and anterior capsulorhexis contracture, perhaps due to a greater than average fibroblastic, proliferative metaplasia of residual lens epithelial cells into myofibraoblasts. Other complications include posterior vitreous membrane. Case reports of patients undergoing multiple YAG laser capsulotomies to treat recurrent PCO have been reported.

Pathophysiology

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Primary prevention

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Diagnosis

Electromyography demonstrating typical myotonic discharges.

History

Sustained muscle contraction (myotonia) exacerbated by excitement, extreme temperatures and fatigue.

Physical examination

Hand shake – difficulty with release. General appearance - muscle wasting and frontal balding. ‘Hatchet Face’ appearance due to temporalis and masseter muscle wasting. Lids - blepharoptosis. Extraocular movements – ophthalmoplegia Pupils – miosis, slowly responsive to light. IOP – possible low pressure. Dilated exam – Cataract, pigmentary retinopathy.

Signs

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Symptoms

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Clinical diagnosis

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Diagnostic procedures

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Laboratory test

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Differential diagnosis

CPEO INO

Management

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General treatment

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Medical therapy

Due to pulmonary, cardiac, endocrine, and central nervous system involvement, these patient should be referred to specialty care.

Medical follow up

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Surgery

Exercise caution with ptosis repair. Frontalis wasting makes a frontalis sling less successful.

Surgical follow up

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Complications

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Prognosis

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Additional Resources

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References

1. Myopathies without EOM Weakness: Facioscapulohumeral + Myotonic Dystrophy. Washington University at St. Louis. 2014 June. Web. http://neuromuscular.wustl.edu/musdist/pe-eom.html. 2. Pelargonio G, Dello Russo A, Sanna T, De Martino G, Bellocci F. Myotonic Dystrophy and the Heart. Heart. 2002 Dec; 88(6): 665–670. 3. Cohen, A, Weinberg D. Evaluation and Management of Blepharoptosis. New York: Springer; 2011. 79 p. 4. Sorge A, Devoelaere T, Sotodeh M, et. all. Exposure keratopathy following silicone frontalis suspension in adult neuro- and myogenic ptosis. Acta Ophthalmol. 2012; 90: 188-192. 5. Versino M, Rossi B, Beltrami G, et. all. Ocular Motor Mytonic Phenomenon in Mytonic Dystrophy. J Neurol Neurosurg Psychiatry 2002; 72:236-240. 6. Azuara-Blanco A, Katz LJ, Arkfeld DF, Walsh TJ. Myotonic dystrophy mimicking bilateral internuclear ophthalmoplegia. Neuro-ophthalmology 1997; 17:11-14. 7. Burian HM, Burns CA. Ocular changes in myotonic dystrophy. Am J Ophthalmol 1967; 63: 22-34. 8. Verhagen WIM, Ter Bruggen JP, Huygen PLM. Oculomotor, auditory, and vestibular responses in myotonic dystrophy. Arch Neruol 1992; 49:954-960. 9. Rosa N, Lanza M, Borrelli M, et. all. Low Intraocular Pressure Resulting from Ciliary Body Detachment in Patients with Myotonic Dystrophy. Ophthalmology. 2011 Feb;118(2):260-4. 10. Sarks J, Liu H, Killingsworth M, et. all. Retinal Changes in Myotonic Dystrophy: A Clinicomorphological Study. Australian and New Zealand Journal of Ophthalmology, 13: 19–36. doi: 10.1111/j.1442-9071.1985.tb00395.x 11. Rhodes J. Cataract in Myotonic Dystrophy. International Myotonic Dystrophy Organization, Inc. Web. http://myotonicdystrophy.com/wp/wp-content/uploads/2012/09/Cataract-Brochure-Myotonic-Dystrophy.pdf 12. Vassilopoulos D, Alevizos B, Spengos M. Cataract and gamma-glutamyl cycle in myotonic dystrophy. Ophthalmologica. 174 (3); 167-9.