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Muscular dystrophy

Dystrophia myotonica

 Autosomal dominant, probably with incomplete penetrance

Clinical features

  •  onset at any age. Most patients 20-30 years
  • onset dominated by weakness or myotonia or both

  •  difficulty releasing grip may present problems if delicate skills required. If manual work involved weakness tends to be the greater problem

  •  in most cases arm flexors are myotonic and extensors are weak

  •  frontal baldness

  •  loss of facial expression

  •  ptosis

  •  marked wasting of masseters and temporalis produces haggard wasted “hatchet” face

  •  cataracts

  •  dysarthria due to myotonia of tongue

  •  sternomastoid wasting is a prominent early feature. Produces swan neck

  •  percussion of tongue or thenar eminence produces dimpling and slow myotonic contraction of muscle

Picture

Non-neurological features

  • gynaecomastia

  •  gonadal atrophy

  •  cardiac abnormalities: cardiomyopathy and conduction defects

  •  motility disorders of bowel and biliary tree

  •  respiratory infections common due to respiratory muscle involvement and occasional abnormalities in immunoglobulins

  •  many patients have low IQ and dementia may occur

  •  diabetes mellitus due to end-organ unresponsiveness to insulin

  •  ± nodular thyroid goitre

Diagnosis

  • usually unmistakable on clinical grounds alone

  •  EMG changes easily detectable in almost any muscle: “dive bomber” pattern

Treatment

  • procainamide or phenytoin relieve myotonia in some patients but don’t alter progression of disease

Anaesthetic management

Respiratory muscle weakness

  • respiratory function. should be fully assessed pre-op. and respiratory depressants (eg thiopentone or opioids) should be used with care.

  • there is increased sensitivity to non depolarising muscle relaxants

  • elective IPPV may be required

  • post-op. care of the airway must be meticulous because of muscle weakness

  • chest infections are common

  • elective ITU admission advisable

Cardiovascular effects

  • arrhythmias common

  • cardiomyopathy

Muscle spasm

  • may be provoked by depolarising muscle relaxants or anti-cholinesterases, therefore avoid suxamethonium and neostigmine

  • not abolished by non-depolarising relaxants

CNS

- very sensitive to thiopentone with 50-100 mg causing apnoea

Duchenne muscular dystrophy

Sex linked recessive. Very rare female cases reported

Clinical features

  • onset between 3 and 10 years of age

  • most die within 10 years of onset

  • initially involves proximal muscles of legs. Later shoulder girdle and then extends peripherally

  • contractures occur early and are severe

  • loss of reflexes except ankle jerks

  • diaphragm, neck, extraocular and facial muscles very rarely involved

  • macroglossia in some cases

  • pseudohypertrophy of calves, occasionally deltoid and infraspinatus

  • bone thinning, pathological #s, fatty infiltration of the heart and respiratory infections are important complications

  • 30% have IQ <75

  • CPK very high initially with a later fall into the normal range when atrophy is severe

  • carrier state may be detected by high CPK and EMG.

 

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©Charles Gomersall, March, 2007 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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