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Myasthenia gravis

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  • 1. Myasthenia Gravis Examination Statement Examine face, CNs eyes Approach to Ptosis (See Ptosis) and weakness Sequence Eyes Ptosis with fatigability Variable strabismus and diplopia that occurs after some time Check for hyperthyroid and thyroid eye disease Check for anaemia Check for malar rash of SLE Face VII – show your teeth : snarls Assessment of speech : Yeeee or count 1 to 20, nasal voice (bulbar palsy) Masseter weakness but pterygoids normal Check neck for goitre and scars ULs Normal deep tendon reflexes (Eaton Lambert and Miller Fisher are reduced) Normal sensation Fatigability with weakness RA and SLE features Thymectomy scar and plasmapheresis line Associations Endo: Thyroid, DM, Pernicious anaemia CTD: RA, SLE, Polymyositis Requests Drug Hx D-penicillamine usage for RA or Wilson’s Antibiotics and CVS drugs that can worsen MG Temperature chart for fever – precipitate weakness Presentation Sir, this patient has myasthenia gravis as evidenced by presence of muscle weakness with fatigability. The patient’s deep tendon reflexes and sensation are normal. On examination of the face, there is presence of bilateral facial muscle weakness producing a mask-like facies with ptosis. I noticed furrowing of her forehead musculature in an attempt to compensate for the ptosis. There is presence of variable strabismus and diplopia after sustained gaze. I also noticed the presence of a nasal voice as well as a reduction in volume of his speech when asked to count from 1 to 20. The patient does not require a nasogastric tube. I did notice mid line sternotomy scar which suggest previous thymectomy. There is no goitre or features of hyperthyroidism. Patient also does not have symmetrical deforming polyarthropathy to suggest RA and has no cutaneous features of SLE. I also did not notice any diabetic dermopathy.
  • 2. I would like to complete my examination by Checking his negative inspiratory force Temperature chart Drug history In summary, this patient has myasthenia gravis with mild weakness of which a thymectomy has been done previously. Questions What is Myasthenia Gravis? Autoimmune condition with antibodies targeting the post-synaptic Ach receptors of the neuromuscular junction Resulting in progressive muscle weakness with use of the muscle and recovery of strength after a period of rest Weakness experienced once number of receptors is 30% or less How common is the thymus involved? 75% of cases of which 15% are thymomas and 85% are thymic hyperplasia What are the common presentations? Age 2 peaks 20 to 30 years old with female predominance >50 years old with male predominance Ptosis, diplopia Dysarthria, difficulty swallowing (isolated bulbar muscles involvement occurs in 20%) Generalised weakness or reduced exercise tolerance Respiratory failure in 1% Tends to occur extraocular muscles first, then to facial to bulbar and to limbs and truncal What can exacerbate MG or precipitate crisis? Non compliance to medications Infection Emotions Drugs Antibiotics: aminoglycosides, tetracyclines, macrolides and fluoroquinolones CVS : Beta blockers, Calcium channel blockers (verapamil) Others : Chloroquine, quinidine, procainamide, Li, Mg, Prednisolone, quinine(in gin tonic drinks), penicillamine What is cholinergic crisis? Can cause confusion between myasthenic crisis from cholinergic crisis Results from excess of cholinesterase inhibitors such as neostigmine and physostigmine Causes flaccid paralysis and SLUDGE (Miosis, salivation, lacrimation, urinary incontinence, diarrhea, gastrointestinal hypermotility and emesis)
  • 3. How would you investigate? Blood Ix AchR Ab Positive in 80% with generalised MG Positive in only 50% with ocular involvement only also present in 90% of patients with penicillamine induced MG Antistriated musce Ab Anti Muscle specific kinase Ab (Anti MuSK Ab – positive in patients with AchR Ab –ve) FBC to rule out infection Imaging CXR – thymus (anterior mediastinal mass), aspiration pneumonia CT for thymus Tensilon test Dx and distinguishing from cholinergic crisis Edrophonium (T1/2 10 mins) Look for objective improvement in ptosis (require observer) Cardiac monitoring for bradycardia and asystole (Rx with atropine) 1 mg test dose and up to 10 mg In cholinergic crisis, will get increased salivation etc Note that in ALS, improvement in muscle weakness also occurs Ice Pack test Ice applied with glove to eyelids for 2 mins Improvement in ptosis is dx (positive in 80%) Electrodiagnostic studies Repetitive nerve stimulation test – shows a decrease in the compound muscle action potential by 10% in the 4th or 5th response to a train of nerve stimuli Single fibre nerve electromyography – evidence of neuromuscular blockade with increased jitter How do you grade the severity of the weakness? Myasthenia Gravis Foundation of America o Grade 1 – affects the ocular muscles only o Grade 2 – mild weakness affecting muscles other than ocular muscles 2A – Affects the limb and axial muscles 2B - Affects the respiratory and bulbar muscles o Grade 3 – moderate weakness (3A AND 3B) o Grade 4 – Severe weakness (4A and 4B) o Grade 5 – Intubation required Osserman’s grading o I: Ocular o II A: Mild generalised with slow progression o II B: Moderate generalised o III: Acute fulminant MG o IV: late severe MG (takes 2 yrs to progress from I to II) How would you manage? Emergencies in crisis (ABC) Treat exacerbating factors Stop medications that can exacerbate
  • 4. Treat fever with antipyretics Treat infections Oral pyridostigmine, neostigmine Steroids, azathioprine, cyclosporine Plasmapheresis IVIG Thymectomy What are the complications? Myasthenic crisis Severe exacerbation of MG 10% require intubation Treatment complications Cholinergic crisis Cx of medications What is Eaton-Lambert syndrome? Myasthenic disorder associated with malignancy such as small cell ca of lung Affects the proximal (especially the pelvic girdle and thigh) and truncal musculature; bulbar muscles is rarely involved Improves with exercise Presence of Abs to calcium channels