MYOTONIC DYSTROPHY

Background
Medical Management Considerations
References
Resources for Families
Advisory Committee
Publication Information

Learning Points

  • Restate the occurrence of Myotonic Dystrophy (1:10,000 to 1:8,000 births) and that there is a 50% chance an affected individual will transmit the disease to his or her offspring (autosomal dominant pattern of inheritance).
  • Describe the etiology of Myotonic Dystrophy (e.g., caused by a mutation on the myotonin protein kinase gene, involving unstable trinucleotide repeats on chromosome 19; the greater the length of expansion, the more severe are the characteristic features).
  • Recognize that, except in congenital cases, physical disability rarely becomes severe until fifteen to twenty years after the onset of symptoms.
  • List five characteristic features of Myotonic Dystrophy; e.g.,
    • Myotonia, especially “grip” myotonia
    • Muscle atrophy (beginning with face, neck, hands, forearms, and feet)
    • Muscle weakness (esp. facial and distal), with ptosis, facial diplegia, and elongated facies and tented upper lip
    • Abnormal gait
    • Cataracts
  • Describe next steps when a diagnosis of Myotonic Dystrophy is clinically suspected:
    • Perform complete physical and neurological exam to detect anomalies
    • Assess family medical history
    • Confirm diagnosis with DNA probe
  • Refer patients for physical and occupational therapy evaluation and therapy need.
  • Refer families to appropriate resources on Myotonic Dystrophy.

BACKGROUND
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Description and Cause

Myotonic dystrophy, the most common adult form of muscular dystrophy, is an inherited neuromuscular disorder in which muscles contract but have decreasing power to relax along with other physical and intellectual implications. Myotonic dystrophy is caused by a mutation on the myotonin protein kinase gene, involving unstable trinucleotide repeats on chromosome 19; the greater the length of expansion, the more severe are the characteristic features. It follows an autosomal dominant pattern of inheritance. There can be considerable variability among affected individuals, even within the same family. There appears to be increased severity of symptoms and decreased age of onset within families as the condition is transmitted to younger generations. The disease is rarely congenital, most often developing some time after birth. However, affected infants may demonstrate severe hypotonia in the newborn stage. Half of affected individuals show visible signs by age 20, while half do not develop symptoms until after age 50.

Occurrence

  • 1:10,000 to 1:8,000 births
  • There is a 50% chance that an affected individual will transmit the disease to his or her offspring.

Diagnosis

Electromyography will generally support clinical suspicion of the disease, and diagnosis may be confirmed by DNA probe analysis on blood.

Characteristic Features

Note: Except in congenital cases, physical disability rarely becomes severe until fifteen to twenty years after the onset of symptoms. The higher the age of onset, the slower is the progression of the disease and the less serious are the consequences.

  • Myotonia, especially “grip” myotonia
  • Muscle atrophy (beginning with face, neck, hands, forearms, and feet)
  • Muscle weakness (esp. facial and distal), with ptosis, facial diplegia, and elongated facies and tented upper lip
  • Abnormal gait
  • Cataracts
  • Cardiac dysfunction (ventricular tachycardia, ventricular arrhythmias, mitral valve prolapse, conduction blocks)
  • Hypoactive or absent deep tendon reflexes
  • Orthopedic malformations (talipes equinovarus)
  • Premature balding
  • Testicular atrophy
  • Mental retardation (especially if congenital)
  • Hypersomnolence
  • Respiratory impairment (especially in infants)

Possible Associations

  • Obstetric complications (miscarriage, abnormal placentation, perinatal asphyxia)
  • Gastrointestinal disorders (reflux, dysphagia, intestinal pseudo-obstruction syndrome, etc.)
  • Type-II diabetes mellitus
  • Recurrent pneumonia
  • Adverse reaction to anesthesia
  • Psychiatric disorders (personality disorders, depression, etc.)
  • Underdeveloped social skills
  • Sudden death (resulting from cardiac dysfunction)

MEDICAL MANAGEMENT CONSIDERATIONS
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Note: These considerations are in addition to the normal medical care provided to an individual without Myotonic Dystrophy. Although many recommendations can be addressed through clinical examination by the primary care provider, a multidisciplinary team approach (primary care physician, neurologist, pulmonologist, physical therapist, occupational therapist, nurse, orthopedist, social worker) is recommended for persons with Myotonic Dystrophy. Multidisciplinary care may be obtained through programs such as California Children Services (CCS) or clinics funded by the Muscular Dystrophy Association.

Upon Diagnosis

Because most cases of myotonic dystrophy are adult-onset and clinical expression varies so widely, recognition and diagnosis may not be possible until well after birth. In any case, the following should be performed as soon as diagnosis is clinically suspected:

  • Perform complete physical and neurological exam to detect anomalies
  • Assess family medical history
  • Confirm diagnosis with DNA probe
  • Once diagnosis is confirmed assess cardiac function anomaly; if symptoms of cardiac dysfunction are present, refer to cardiologist
  • Assess muscle function & muscle astrophy
  • Provide genetic counseling, including discussion of recurrence risk
  • Refer infants to early intervention programs and all affected persons to Myotonic Dystrophy and/or disability support groups
  • Discuss possibility of SSI enrollment

Ongoing (all ages)

  • Refer for physical and occupational therapy evaluation, and therapy need
  • Durable medical equipment options
  • Refer for psychological evaluation as needed
  • Monitor respiratory function; consider noninvasive ventilation as needed
  • Recommend epidural anesthesia as an alternative to general anesthesia in surgery to prevent cardiorespiratory complications
  • Recommend mild exercise as long as no pain or exhaustion is experienced
  • Refer to nutritionist or registered dietician because of increased caloric requirements

Childhood (1 to 13 years, if applicable)

  • Monitor school progress, if applicable

Adolescence and Adulthood (13 years and over)

  • Ensure that pregnant females receive constant obstetric monitoring and are advised to deliver in sites with perinatal facilities
  • Discuss long-term financial plans
  • Discuss alternative community living resources
  • Monitor prevocational training and vocational activities
  • Discuss community-supported employment opportunities

REFERENCES
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Peer-reviewed Journal Articles/Academies

Broughton, R., Stuss D., Kates M., Roberts J., Dunham W. (1990). Neuroopsychological Deficits and Sleep in Myotonic Dystrophy. Canadian Journal of Neurological Sciences, 17(4), 410-5

George, A., Schneider-Gold, C., Zier, S., Reiners, K., Sommer C. (2004) Musculoskeletal Pain in Patients with Myotonic Dystrophy Type 2. Archives of Neurology 61(12). 1938-1942.

Machuca-Tzili, L., Brook, D., Hilton-Jones D. (2005) Clinical and Molecular Aspects of the Myotonic Dystrophies: a review, Muscle & Nerve, 2005 32(1), 1-18

Motlagh, B., MacDonald, J.R., Tarnopolsky M.A. (2005). Nutritional Inadequacy in Adults with Muscular Dystrophy. Muscle & Nerve, 31(6), 173-178.

Phillips, M.F., Harper, P.S. (1997). Cardiac Disease in Myotonic Dystrophy. Cardiovascular Research, 33(1), 13-22.

Ptacek, L.M, et al. (1993). Genetics and Physiology of the Myotonic Muscle Disorders. New England Journal of Medicine, 328(7), 482-489.

Reifer H., Sobel, E. (1998). Contrasts in Clinical Presentation and Genetic Transmission of Myotonic Dystrophy. Journal of the American Podiatric Medical Association, 88(7), 313-322.

Rudnik-Schoneborn S., et al. (1998). Different Patterns of Obstetric Complications in Myotonic Dystrophy in Relation to the Disease Status of the Fetus. American Journal of Medical Genetics, 80(4), 314-321.

Skocyzlas L.J., Langlais R.P., Young R.S. (1985). Mytonic Dystrophy: Review of the Literature and New Radiographic Findings. Dentomaxillofacial Radiology, 14 (2), 101-108.

Wiles, C.M., Busse, M.E., Sampson, C.M., Rogers, M.T., Fenton-May J., van Deursen R. (2005). Falls and Stumbles in Myotonic Dystrophy. Journal of Neurology, Neurosurgery and Psychiatry. Retrieved November 2, 2005.

Special Interest Groups/Other Publications

Bird T.D. (2004) Myotonic Dystrophy Type 1. Retrieved January 23, 2006.

Capute, A. J., Accardo, P.J. (1996). Developmental Disabilities in Infancy and Childhood vol. I. Neurodevelopmental Diagnosis and Treatment. Baltimore: Paul H. Brookes Publishing Co.

Capute, A.J., Accardo, P.J. (1996). Developmental Disabilities in Infancy and Childhood vol II. The Spectrum of Developmental Disabilities. Baltimore: Paul H. Brookes Publishing Co.

Griesemer, D. A., Waheed, N. (1999). Muscular Dystrophy. In M.R. Dambro (Ed.) Griffith’s 5-Minute Clinical Consult. Baltimore: Lippincott Williams & Wilkins, pp. 704-705.

May, P.B. Jr., (1999) Myotonic Dystrophy Developmental Medicine Clinic syllabus. UMD New Jersey, Robert Wood Johnson Medical School. Retrieved January 20, 2006.

Moxley, R.T. (1997). Myotonic Disorders in Childhood: Diagnosis and Treatment. In Carrell-Krussen Symposium invited lecture, Journal of Child Neurology 12(2), 116-129.

RESOURCES FOR FAMILIES
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California Department of Developmental Services
916-654-1690

California Regional Centers
915-654-1958

European Alliance of Muscular Dystrophy Associations

Exceptional Parent Magazine
800-247-8080

March of Dimes Birth Defects Foundation
914-428-7100

Muscular Dystrophy Association (USA)
800-572-1717

Muscular Dystrophy Association of Canada

Muscular Dystrophy Association of South Australia Inc.
800-685-MDA

ADVISORY COMMITTEE
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Theodore A. Kastner, M.D., M.S.
Felice Weber Parisi, M.D., M.P.H.
Mary Ann Lewis, Dr.P.H., R.N., F.A.A.N.
Joan M. Reese, M.D., M.P.H.
Jaime D. Mejlszenkier, MD., F.A.A.N

PUBLICATION INFORMATION
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This document does not provide advice regarding medical diagnosis or treatment for any individual case, and any opinions or statements contained in this document are not intended to serve as a standard of medical care. Physicians are encouraged to view the considerations presented in this document in light of evolving scientific information. This document is not intended for use by the layperson. Reproduction of this document may be done with proper credit given to California Department of Developmental Services.