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Phenotype of Paramyotonia congenita

Phenotype of Paramyotonia congenita. Dr Doreen Fialho, MRCP Clinical Research Fellow MRC centre for Neuromuscular Disease, Institute of Neurology, Queen Square, London UK. Original Description. Eulenburg 1886 German family, 6 generations Mother’s diagnosis. Classical Features.

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Phenotype of Paramyotonia congenita

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  1. Phenotype of Paramyotonia congenita Dr Doreen Fialho, MRCP Clinical Research Fellow MRC centre for Neuromuscular Disease, Institute of Neurology, Queen Square, London UK

  2. Original Description • Eulenburg 1886 • German family, 6 generations • Mother’s diagnosis

  3. Classical Features • Paradoxical exercise and cold induced myotonia • Episodes of paralysis • Autosomal dominant with high penetrance

  4. Distribution • Cranial musculature • myotonia • Upper and lower limbs • short lasting myotonia • Longer lasting paralysis • In LL often followed by fatigue • Most affected face, eyes, pharynx, hands

  5. Other Features • Reduced electrical muscle excitability during attacks • No significant change with age • Occupational restriction

  6. Spectrum vs distinct categories

  7. Triggers • Exercise (rest) • Cold • Potassium • Fasting

  8. Exercise and Myotonia • Worsening during exercise vs warm-up • Absence of warm-up • Worsening after exercise and short period of rest

  9. Pain • Probably underestimated • Usually associated with muscle stiffness and weakness

  10. Diagnosis • Clinical • Neurophysiology (EMG, SET/Cooling) • Genetic analysis (Potassium challenge , muscle biopsy used historically)

  11. Neurophysiology • Protocol Fournier et al. (Ann Neurol 2004 and 2006) • EMG • Repeated SET and cooling - stability of CMAP (PMC vs PAM)

  12. Differential Diagnosis • Myotonic Dystrophy I/II • SJS • Stiff person syndrome • Acquired peripheral nerve hyperexcitability • EA1 with prominent neuromyotonia

  13. Treatment/ Management • Mexiletine (myotonia) • As required • ECG monitoring, side effects • Acetazolamide (paralysis) • Lifestyle advice • Genetic counselling • Anaesthesia advice

  14. Anaesthesia • Problems • MH like reaction - myotonic crisis • Post-op respiratory depression/paralysis • Avoidance of triggers • Drugs - depolarising agents (suxamethonium), anticholinesterases, opiods • Temperature • Immobility (general vs local anaesthetic, post-op mobilisation, length of procedure) • Potassium levels

  15. Classification • PMC - paralytic/non-paralytic vs Sodium channel myotonias • Potassium aggravated myotonias • Myotonia Fluctuans • Myotonia permanens • Acetazolamide responsive myotonia

  16. PAM vs PMC • PAM range between clinically similar to Myotonia congenita to paradoxical myotonia similar to PMC • Defining difference presence of exercise/cold induced decrease in muscle excitability • Episodes of weakness • Progressive CMAP decrement after SET (cooling)

  17. PAM • Distinction to MC • Fluctuation • Absence or less pronounced warm-up • Absence transient weakness • (potassium sensitivity) • (dominant inheritance) • Distinction to PMC • Absence of weakness

  18. Acknowledgement • MRC Centre - Prof M.G.Hanna • Clinical Research Fellows - Dr E.Matthews • Clinical Neurophysiologist - Dr V.Tan • Funding : • NSCAG • MRC, Wellcome, CINCH

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