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JUVENILE MYASTHENIA GRAVIS

JUVENILE MYASTHENIA GRAVIS. DR JANE NYAWIRA, DR JANE HASSELL GERTRUDE’S CHILDREN’S HOSPITAL. INTRODUCTION. Neuromuscular conditions affect peripheral nerves, neuromuscular junction or muscle Any muscle group can be affected; presentation can be focal or generalized

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JUVENILE MYASTHENIA GRAVIS

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  1. JUVENILE MYASTHENIA GRAVIS DR JANE NYAWIRA, DR JANE HASSELL GERTRUDE’S CHILDREN’S HOSPITAL

  2. INTRODUCTION • Neuromuscular conditions affect peripheral nerves, neuromuscular junction or muscle • Any muscle group can be affected; presentation can be focal or generalized • Myasthenia gravis is an example of a treatable neuromuscular condition

  3. CASE: 8-year old girl • Presented with acute cough and difficulty in breathing • Initially admitted & treated as severe pneumonia, required intubation & mechanical ventilation • Subsequent failed exubations x2 with CO2 retention – no lung pathology identified • Noted to have weak gag, weak cough, inability to swallow

  4. CASE: Examination • Alert, following commands • Absent cough/gag, bilateral facial weakness and ptosis, diurnal variation noted – better after sleep • Mild fluctuating proximal limb weakness, normal tone and reflexes, no additional movements

  5. CASE: Acute differentials for multiple cranial neuropathies • Miller Fischer Syndrome (GBS variant affecting cranial nerves) • Bickerstaff’s brainstem encephalitis (BBE), can affect cranial nerve nuclei) • Brainstem tumour or demyelination • Riboflavin transporter deficiency (BVVL, Brown Vialetto Van Laere) • Fazio-Londe disease(progressive bulbar palsy)

  6. CASE: Assessment • MRI brain normal – ruled out Bickerstaff’s encephalitis • CSF studies normal – protein not raised so Miller Fischer less likely • TFTs, CK, LFTs and lactate normal

  7. CASE: Further history on direct questioning • 6 month history of poor cough, difficulty swallowing, slow feeding. • Intermittent drooping eyelids, tilting head back to watch TV. • Easy fatigability, wobbly walking towards the end of the day. • Fall while walking , unable to get up but alert. • Treated for “acute wheeze” 2 months prior.

  8. CASE: Progress • Clinical diagnosis of Myasthenia Gravis based on history of fluctuating fatigable weakness. • Symptom freedom achieved with pyridostigmine (empiric) • Physiotherapy & occupational therapy • Anticholinesterase antibodies positive • CT chest: No thymic enlargement • Discharged under Neurologist follow up, returned to school

  9. MYASTHENIA GRAVIS (MG) • Autoimmune disease. • 5-20 per 100,000, uncommon in children. • Antibodies against postsynaptic membrane of the NMJ interfere with nerve impulse transmission leading to varying muscle weakness & fatigability. • Antibodies against nicotinic acetylcholine receptors (AChR), muscle-specific receptor tyrosine kinase (MuSK), or others.

  10. JUVENILE MYASTHENIA GRAVIS (JMG) • < 18 years of age, estimated incidence: 1/200,000-1,000,000 • May be more common in African populations • Pre-pubertal JMG (onset <12years) • Equal male to female ratio • Isolated ocular symptoms(50%) • Lower frequency of AChR antibodies (none in 30-50%) • May spontaneously remit

  11. PRESENTATION • Painless, fluctuating & fatiguable muscle weakness • Worse with physical activity, repetitive movements & towards end of the day. • Improves after periods of rest • Chronic course with remission & relapses. • May be acute severe requiring ICU.

  12. PRESENTATION • Ocular : (75%) ptosis, diplopia, asymmetric ophthalmoplegia, lid twitch. • Bulbar : Dysphagia, velopharyngeal insufficiency, difficulty chewing, dysphonia, nasal speech, dysarthria, hypophonia. • Generalized: Fatigable proximal limb weakness. • Myasthenic crisis: Paralysis of the respiratory muscles. • Enlarged thymus or thymoma in 75%, check for symptoms of associated autoimmune disorders

  13. MAKING THE DIAGNOSIS • High index of clinical suspicion • Response to treatment – pyridostigmine or edrophonium • Antibodies to AChR, MuSK, LRP4 – may be negative • Repetitive nerve stimulation • Single fibre electromyography

  14. TREATMENT • 1st line: Acetylcholinesterase inhibitors e.g. Pyridostigmine • 2nd line: If breakthrough symptoms on max dose pyridostigmine, add immune suppression • Steroids for acute exacerbations • Steroid sparing long-term e.g. azathioprine, mycophenolate mofetil • IVIg or plasmapheresis if drug-resistant • Acutely may need ventilation • Thymectomy cures some

  15. CONCLUSION: JMG • JMG is a rare, treatable neuromuscular condition that frequently presents with isolated ocular or bulbar symptoms • Important aspects specific to the pediatrics: • Distinct clinical features of prepubertal presentations • Different rates of AChR seropositivity • Response to therapy, remission rates • Serology may be negative, start empiric pyridostigmine and seek help

  16. References • Finnis, Maria F, and Sandeep Jayawant. “Juvenile myasthenia gravis: a paediatric perspective.” Autoimmune diseases vol. 2011 (2011): 404101. doi:10.4061/2011/404101 • Clinical Characteristics of Pediatric Myasthenia: A Surveillance Study. Juliana VanderPluym, Jiri Vajsar, Francois Dominique Jacob, Jean K. Mah, Danielle Grenier, Hanna Kolski.Pediatrics Oct 2013, 132 (4) e939-e944; DOI: 10.1542/peds.2013-0814

  17. THANK YOU

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