Myotonic Dystrophy

You may be asked to examine a patient with eyelid drooping, weakness, family history of weakness etc.


You may be asked to start by examining the cranial nerves.


If you notice ptosis, proceed as follows:


  • Inspect: ptosis (uni/bilateral, symmetrical/asymmetrical, partial/complete),eye position, pupils (size: big in CN III palsy, small in Horners, normal in myasthenia/myotonic dystrophy/CN III palsy)
  • Eye movements and ask if gets double vision (observe for [complex] opthalmoplegia) and fatiguability on looking up for 20 seconds (myasthenia). Make a point of testing CN 4 (ask to look down and in) and CN 6 (ask to look laterally)
  • Can offer fundoscopy (cataracts)
  • CNs V, VII, VIII, IX, X, XI, XII
  • Neuro assessment of the arms: wasting, tone (reduced), power (reduced distally more than proximally), reflexes (reduced/absent in myotonic dystrophy), coordination, sensation (sensation is normal in myasthenia and myotonic dystrophy)
  • Neuro assessment of the lower limbs as above plus gait (bilateral foot drop may be evident)
  • Extra tests for myotonic dystrophy:
    • Shake patient’s hand (delay before grip release), ask to repeatedly open and close fist
    • Percussion myotonia (use tendon hammer to tap thenar eminence, the thumb flexes)
    • Pulse check, look for diabetic fingerpick marks
    • Face and neck: frontal balding, myopathic facies, cataracts, palpate temporalis and masseter when patient clenches teeth (wasted and weak), palpate sternocleidomastoid (wasted and weak) and observe/palpate for a goitre. Ask to close eyes tightly then open (delayed eye opening)
    • Chest: gynaecomastia, apex beat, PPM scar, auscultate heart sounds (murmur), auscultate lungs (bronchiectasis)
    • Abdomen: eg. for PEG
  • Extra myasthenia tests to exclude myaesthenia:
    • Test eye closure (peek sign) and test lip closure
    • Neck flexion and extension against resistance. Jaw supporting sign.
    • Test power of elbow flexion/extension, shoulder abduction. Ask to do ‘chicken wing arm exercises 10-20 times’ then retest power (weaker after exercise).
    • Test speech (count to 50) ?fatiguability
    • Look for a sternotomy scar (thymectomy), spirometer, gastrostomy/NG tube, does the patient appear cushingoid
    • Resp: chest expansion and offer to do FVC
    • Don’t miss evidence of other autoimmune conditions e.g. thyroid, RA, SLE, diabetes

Present to the examiner:


I suspect this patient has myotonic dystrophy as evidenced by:


Characteristic appearance (myopathic facies, frontal balding, ptosis), myotonia, wasting and weakness of facial, neck and limb muscles (distal >proximal), reduced/absent reflexes, normal sensation, extra features such as gynaecomastia, pacemaker etc.


To complete the examination I would like to:


Perform fundoscopy (cataracts)

Assess speech and swallow

Examine the external genitalia (testicular atrophy)

Perform full cardiovascular examination

Perform full neurological examination of upper and lower limbs (if not already done)


Differential Diagnosis of ptosis:


  • Myasthenia Gravis (bilateral) NB: fatiguability and no myotonia
  • Myotonic dystrophy (bilateral)
  • Horner’s syndrome
  • 3rd CN palsy
  • Oculopharyngeal muscular dystrophy (bilateral)
  • Mitochondrial disease e.g. Kearns-Sayres (bilateral)


NB: See “Station 5 Ptosis”




Myotonic Dystrophy (MD)


Myotonic Dystrophy (MD) is the most common adult muscular dystrophy.  It is due to expansion of an unstable trinucleotide repeat (CTG) on chromosome 19.

Autosomal dominant. DMPK gene encoding for myotonin protein kinase.

Shows anticipation (worse symptoms and signs in next generations, earlier presentation if increase in repeat length)

Causes abnormally sustained muscle contraction after voluntary contraction ceases.  Worsened by cold/emotions/exercise.

Starts in adulthood (20-30 years old)



Frontal balding, cataracts, bilateral ptosis, facial weakness (myopathic facies), wasting of temporalis and masseter, wasted and weak sternocleidomastoids (swan neck), muscle weakness (proximal and distal), grip myotonia, gynaecomastia, cardiomyopathy and arrhythmias, testicular atrophy, diabetes, peripheral neuropathy, oesophageal/biliary tree/bowel involvement (dysphagia, constipation/diarrhoea, reflux), aspiration and bronchiectasis, nodular thyroid, psych problems, mild intellectual impairment, hypersomnia


Differential Diagnosis: fascioscapulohumeral dystrophy (face and neck weakness, ptosis, winged scapula, hypertrophy of deltoids)



EMG- dive bomber pattern, waxing and waning of potentials.  Repetitive discharges with minor stimulation.

Muscle biopsy- fibre atrophy type 1, no inflammation

CK- normal/mildly elevated

Genetic testing

Associated features: glucose/Hba1c (diabetes), ECG (long PR, long QT, heart block), CXR (cardiomegaly), slit lamp examination (cataracts)



MDT: ophthalmology, gastroenterology, cardiology, respiratory, endocrinology, neurology, SALT, physio, OT, GP, psychiatry, geneticist

Medical: phenytoin/ quinine/ procainamide/ mexiletine for myotonia

Manage complications eg. pacemaker for heart block, diabetes, obstructive sleep apnoea

Screen relatives

Surgical: anaesthesia is high risk, cataract removal



Written by Dr Sarah Kennedy


Resources used to write this document are listed in the references section of this webpage