Muscular Dystrophies

Myotonic Dystrophy

Background

• There are two types of muscular dystrophy, both caused by a genetic abnormality inherited in an autosomal dominant inheritance

• Type 1: CTG repeat, DNPK gene on chromosome 19 that features anticipation, presenting with distal weakness

• Type 2: abnormality in gene ZNFP9 on chromosome 3, presenting with proximal weakness

• Complications

  • Cardiac: AF, heart block

  • Endocrine: diabetes, thyroid and gonadal disorders

  • Eyes: cataracts

• Prognosis: reduced due to cardiac & respiratory complications

Assessment

Presentation

• Progressive muscle weakness from adolescence or adulthood

Examination

• Muscle weakness in UL, LL & face

  • Myotonia- handshake, unable to open fingers/ eyes quickly

  • Muscle wasting in face (masseter)- myopic face; UL/ LL wasting,

  • Ptosis with head tilting backwards due to neck weakness, dysarthric speech,  

  • Tone: reduced/ normal, Reflexes: reduced / absent,

  • Mobility aids

  • Normal sensation & co-ordination, 

  • Testicular atrophy

• Frontal balding

• Cataracts, irregular pulse,

Investigations

• CK- mildly raised (500)

• EMG- myopathic discharges (divebomber changes)

• Muscle biopsy (rarely)

Diagnosis

Diagnostic criteria: genetic testing 

• If strong Family history + clinical suspicion may not be required

• If diagnostic uncertainty, muscle biopsy can be done

Differentials: 

• Ptosis: Myasthenia Gravis, CN III palsy, Horner's Syndrome

• Myotonia: Myotonia congenita 

• Global weakness: Becker's Muscular Dystrophy, Myopathies

Management

MDT

• Consultant Neurologist, Genetics, Endocrinologist, Cardiologist, Respiratory, Palliative Care

• PT, orthotics, OT/ SW, SLT, dieticians

Lifestyle

• Exercises, nutrition- sarcopenia

Medical

• Analgesia- neuropathic pain

• Meloxitine (Na blocker)- can improve myotonia

• Complications: Diabetes, AF

Surgical/ Interventions

• NIV

• PEG

• Cataract removal

Becker's Muscular Dystrophy

Background

• Becker's is caused by reduced or absent dystrophin

• Complications: dilated cardiomyopathy, arrhythmias

• Prognosis: close to normal life expectancy

Assessment

Presentation

• Age 5-15yrs, predominantly male (X linked recessive)

• Ambulatory into adulthood

Examination

• Proximal myopathy (hips, thighs, shoulders)

• 
  

Investigations

• CK: moderately elevated

• Genetic testing

Diagnosis

Diagnostic criteria: ?genetic testing

Management

MDT

• Consultant Neurologist, Genetics, Cardiologist, Respiratory, Palliative Care

• PT, orthotics, OT/ SW, SLT, dieticians

Lifestyle

• Exercises, nutrition- sarcopenia

Medical

• Analgesia- neuropathic pain

• Complications: AF, CHF

Page written in 2024, updated 2026.