myotonic dystrophy 1

Introduction

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
  • no fasciculations
• frontal balding
• cataracts
• cognitive impairment
• generalized fatigue
• decreased libido

* myotonia may be present several years prior to muscle weakness

Laboratory

• DMPK genotyping
  • DMPK gene mutation
  • DMPK gene CTG repeats
• DMPK phenotype
• see ARUP consult

Diagnostic procedures

• electrocardiogram:
  • arrhythmias: atrial arrhythmias, ventricular arrhythmias
  • heart block. first degree heart block
  • bradycardia

Complications

• diabetes mellitus type 2
• hypogonadism, testicular atrophy

Management

• permanent pacemaker or implantable cardioverter-defibrillator may be needed to prevent sudden death

More general terms

• myotonic dystrophy; Steinert disease; myotonia dystrophica