Myotonic Dystrophy

Aka: Myotonic Dystrophy, Steinerts Disease, Myotonia Atrophica, Myotonic Muscular Dystrophy

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II. Epidemiology

  1. Prevalance: 1 in 8,000 to 10,000
    1. Prevalance as common as 1 in 2100 in some references
    2. Most common form of Muscular Dystrophy in adults
  2. Age of onset
    1. DM1 is typically diagnosed in infancy
    2. DM2 is frequently identified at age 20 to 30 years (but may be diagnosed in later adulthood)
  3. Race
    1. Rare in non-white groups

III. Pathophysiology

  1. Genetic mutation is Autosomal Dominant inheritance
  2. Subsequent generations experience worse symptoms

IV. Types: Genetic Mutations

  1. Myotonic Dystrophy 1 (DM1, Steinert Disease)
    1. DMPK Gene Mutation
    2. Typically identified near birth (congenital DM1) and is more severe than DM2
    3. Congenital DM1 is associated with the most significant manifestations
  2. Myotonic Dystrophy 2 (DM2)
    1. CNBP Gene Mutation
    2. More mild than DM1, and typically identified in adulthood
    3. Proximal Muscles are most affected (e.g. neck flexors, hip flexors and extensors)
    4. Muscle pain (myalgias) is more significant in DM2

V. Findings: Muscular

  1. Muscle Weakness
    1. Proximal Muscles are most affected (e.g. neck flexors, hip flexors and extensors) in DM2
    2. Facial Muscle Weakness including Ptosis, Dysarthria, and weak Muscles of Mastication
  2. Myotonia (esp. DM1)
    1. Delayed Muscle relaxation after contraction
  3. Myalgias
    1. Muscle pain is more common in DM2
  4. Muscle Atrophy

VI. Findings: Extramuscular

  1. Cataracts (early onset, before age 50 years old)
  2. Insulin Resistance
  3. Hypersomnia (esp. DM1)
  4. Obstructive Sleep Apnea
  5. Cognitive Deficits (esp. DM1)
    1. Executive Function deficits (e.g. word finding, organization)
  6. Cardiovascular effects
    1. Conduction abnormalities and Blocks
    2. Arrhythmias
    3. Dilated Cardiomyopathy
  7. Men
    1. Premature Balding
    2. Hypogonadism and Infertility

VII. Findings: Congenital DM1

  1. Infancy (diagnosis of congenital DM1)
    1. Hypotonia
    2. Feeding difficulty
    3. Respiratory Failure
    4. Club Foot
  2. Associated Findings at later ages
    1. See Muscular and Extramuscular findings above
    2. Gastrointestinal symptoms (e.g. Diarrhea, Constipation, Encopresis)
    3. Attention Deficit Disorder
    4. Autism Spectrum Disorder
    5. Intellectual Disability

VIII. Diagnosis

  1. Genetic Testing
  2. Lab abnormalities
    1. Serum Creatinine Kinase may be mildly increased
    2. Liver Function Tests elevated in up to 50% of patients
  3. Electrodiagnostic Tests
    1. Motor Nerve Conduction Studies (NCS)
      1. Decreased amplitude, but normal lactency and conduction velocity
    2. Electromyography (EMG)
      1. Rapid spontaneous discharges, waxing and waning in frequency and amplitude (esp. distal Muscles)
  4. Muscle Biopsy
    1. Myopathy

IX. Management

  1. Monitoring
    1. Baseline Electrocardiogram (EKG) and then yearly
    2. Pulmonary Function Tests at baseline and repeat at intervals
      1. Evaluate Pulmonary Function Assessment of Respiratory Muscle Strength
    3. Obstructive Sleep Apnea Screening and consider Sleep Study
    4. Endocrinopathy screening
      1. Diabetes Mellitus Screening
      2. Hypothyroidism screening
  2. Myotonia Management with Sodium Channel Blockers (avoid in AV Block)
    1. Mexiletene
    2. Tricyclic Antidepressants
    3. Benzodiazepines
  3. Referrals as needed
    1. Physical Therapy
    2. Occupational Therapy
    3. Orthotics and Prosthetics
    4. Speech and Language Pathology (Dysarthria)

X. References

  1. Vydra (2022) Myotonic Dystrophy, Stat Pearls, Treasure Island, FL, accessed 7/11/2023
  2. Thornton (2014) Neurol Clin 32(3):705-19 +PMID: 25037086 [PubMed]

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Related Studies

Ontology: Myotonic Dystrophy (C0027126)

Definition (MSH) Neuromuscular disorder characterized by PROGRESSIVE MUSCULAR ATROPHY; MYOTONIA, and various multisystem atrophies. Mild INTELLECTUAL DISABILITY may also occur. Abnormal TRINUCLEOTIDE REPEAT EXPANSION in the 3' UNTRANSLATED REGIONS of DMPK PROTEIN gene is associated with Myotonic Dystrophy 1. DNA REPEAT EXPANSION of zinc finger protein-9 gene intron is associated with Myotonic Dystrophy 2.
Definition (CSP) autosomal dominant neuromuscular disorder which usually presents in early adulthood, characterized by progressive muscular atrophy (most frequently involving the hands, forearms, and face), myotonia, frontal baldness, lenticular opacities, and testicular atrophy; cardiac conduction abnormalities, diaphragmatic weakness, and mild mental retardation may also occur; congenital myotonic dystrophy is a severe form of this disorder.
Concepts Disease or Syndrome (T047)
MSH D009223
ICD10 G71.11
SnomedCT 155096007, 267713009, 77956009
English Dystrophia Myotonica, Myotonia Atrophica, Myotonia Dystrophica, Dystrophies, Myotonic, Myotonic Dystrophies, Dystrophy, Myotonic, myotonia atrophica, DM, DYSTROPHIA MYOTONICA, Myotonic Dystrophy, myotonic dystrophy (diagnosis), myotonic dystrophy, Myotonia atrophica, Dystrophia myotonica [Steinert], Myotonic Dystrophy [Disease/Finding], disease steinerts, myotonia dystrophica, dystrophia myotonica, dystrophy myotonic, Myotonia Atrophicas, Myotonia Dystrophicas, Dystrophia Myotonicas, Myotonica, Dystrophia, Atrophica, Myotonia, Dystrophica, Myotonia, Myotonicas, Dystrophia, Atrophicas, Myotonia, Dystrophicas, Myotonia, Myotonic dystrophy, Dystrophia myotonica, Myotonia dystrophica, DM - Dystrophia myotonica, atrophica; myotonia, dystrophica; myotonia, dystrophy; myotonic, myotonia; atrophica, myotonia; dystrophica, myotonic; dystrophy
Swedish Myotonisk dystrofi
Czech myotonická dystrofie, myotonia atrofica, Myotonická dystrofie, dystrofická myotonie, atrofická myotonie, Steinertova nemoc, myotonická svalová dystrofie
Finnish Myotoninen dystrofia
Italian Malattia di Steinert, Miotonia distrofica, Miotonia atrofica, Distrofia miotonica
Russian KURSHMANNA-BATTENA-SHTEINERTA BOLEZN', DISTROFIIA MIOTONICHESKAIA, MIOTONIIA DISTROFICHESKAIA, MIOTONICHESKAIA DISTROFIIA, ДИСТРОФИЯ МИОТОНИЧЕСКАЯ, КУРШМАННА-БАТТЕНА-ШТЕЙНЕРТА БОЛЕЗНЬ, МИОТОНИЧЕСКАЯ ДИСТРОФИЯ, МИОТОНИЯ ДИСТРОФИЧЕСКАЯ
Japanese シュタイネルト病, 先天性筋緊張性ジストロフィー, 筋強直性ジストロフィー, 筋緊張症-萎縮性, 筋緊張性異栄養, 筋緊張性異栄養症, 萎縮性筋緊張症, 萎縮性ミオトニー, 緊張筋異栄養症, 緊張筋ジストロフィー, 萎縮性筋緊張, 異栄養性ミオトニー, 筋緊張性ジストロフィー-先天性, 緊張性筋ジストロフィー, 緊張亢進型筋萎縮, 緊張亢進型筋萎縮症, 緊張筋ジストロフィ, 筋強直性ジストロフィ, 筋緊張性ジストロフィ, 緊張筋異栄養, スタイナート病, ｷﾝｷｮｳﾁｮｸｾｲｼﾞｽﾄﾛﾌｨｰ, Steinert病, 筋緊張性ジストロフィー
Spanish Distrofia miotónica, distrofia miotónica, Distrofia Miotónica
Portuguese Distrofia miotónica, Distrofia Miotônica, Doença de Steinert
Dutch myotone dystrofie, dystrophia myotonica, atrophica; myotonie, dystrofie; myotoon, dystrophica; myotonie, myotonie; atrophica, myotonie; dystrofie, myotonie; dystrophica, Dystrophia myotonica, Myotonische dystrofie, Steinert-ziekte
German myotone Dystrophie, Dystrophia myotonica, Myotone Dystrophie, Myotonia atrophica, Myotonia dystrophica, Steinert-Krankheit, Batten-Steinert-Syndrom, Curschmann-Steinert-Batten-Syndrom, Curschmann-Steinert-Syndrom
Croatian MIOTONIČNA DISTROFIJA
Polish Dystrofia miotoniczna, Choroba Steinerta, Miotonia zanikowa
Hungarian Myotoniás dystrophia, Dystrophia myotonica
Norwegian Myotonia dystrophica, Steinerts sykdom, Myotonisk dystrofi, Steinert-sykdom, Dystrophia myotonica, Dystrofi, myotonisk, Myotonia atrophica
French Dystrophie myotonique, Myopathie atrophique avec myotonie, Myotonie dystrophique, Maladie de Steinert, DM1 (Dystrophie Myotonique de type 1), Dystrophie myotonique de Steinert, Dystrophie myotonique de type 1, Myotonie atrophique de Steinert
Derived from the NIH UMLS (Unified Medical Language System)

Related Topics in Motor Disorders

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