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myotonic dystrophy 1
Also see myotonic dystrophy
Pathology:
- neurodegenerative disorder
Genetics:
- autosomal dominant
- trinucleotide repeat (CTG) in 3' untranslated region of DM1 gene
Clinical manifestations:
- preferentially involves distal extremities & facial muscles
- muscle weakness, facial weakness*
- myotonia (impaired muscle relaxation)*
- especially grip myotonia
- often worse in cold weather
- tapping of muscle with reflex hammer results in sustained muscle contraction [3]
- no fasciculations
- frontal balding
- cataracts
- cognitive impairment
- generalized fatigue
- decreased libido
* myotonia may be present several years prior to muscle weakness [3]
Laboratory:
- DMPK genotyping
- DMPK gene mutation
- DMPK gene CTG repeats
- DMPK phenotype
- see ARUP consult [2]
Special laboratory:
- electrocardiogram:
- arrhythmias: atrial arrhythmias, ventricular arrhythmias
- heart block. first degree heart block [3]
- bradycardia
Complications:
- diabetes mellitus type 2
- hypogonadism, testicular atrophy [3]
Management:
- permanent pacemaker or implantable cardioverter-defibrillator may be needed to prevent sudden death [3]
General
myotonic dystrophy; Steinert disease; myotonia dystrophica
References
- Medical Knowledge Self Assessment Program (MKSAP) 17, 18.
American College of Physicians, Philadelphia 2015, 2018
- ARUP consult: Myotonic Dystrophy Type 1 (DMPK)
https://arupconsult.com/ati/myotonic-dystrophy-type-1
- NEJM Knowledge+ Neurology
- Kumar A, Agarwal S, Agarwal D, Phadke SR.
Myotonic dystrophy type 1 (DM1): a triplet repeat expansion disorder.
Gene. 2013 Jun 15;522(2):226-30.
PMID: 23570879