Myasthenia gravis Flashcards
What are the typical symptoms/presentations of myasthenia gravis? (5)
Ocular: diplopia (90%), drooping eyelids
Bulbar: choking (weakness of pharyngeal muscle), dysarthria, difficulty chewing, swallowing
Proximal muscle weakness & fatigues
Recurrent pneumonia
Difficult anaesthesia
Myasthenia gravis - PRICMCP
P: droopy eyelids, blurry vision, swallow/chewing difficulties, dysarthria, proximal weakness, dropped head syndrome (progressive weakness of neck muscles)
R: FH, other autoimmune disease
I: how was the dx established? Tensilon (Edrophonium) - Tensilon IV → patient is observed for temporary dramatic improvement of symptoms (now fallen out of favor), blood test (auto-Abs - ACh receptor), EMG (where few needles are inserted to muscles and you are asked to contract/relax muscles)
C: recurrent pneumonia (aspiration), respiratory failure (“myasthenic crisis), ICU admissions. Complications of drug treatments: pyridostigmine → cholinergic crisis, steroids, immunoSx side effects.
M: Pyridostigmine (doses + frequency), steroids, ImmSx, current tx regime, previous PEX and IVIG, doses, previous thymectomy
C: current symptoms, impact on patient’s ADLs, work, social.
P: insights into complications, importance of monitoring symptoms, preventing infections.
Prognosis is good: 50% will have remission, but 5-10% die from RF.
What is the starting & maximal dose of Pyridostigmine for Myasthenia gragis?
30mg QID (starting)
Max 120mg Q4h.
Clinical features of the Cholinergic crisis?
Results from Pyridostigmine toxicity (anti-cholinesterase)
DUMBELLS: basically too many fluids from all orifices of the body + Bradycardia
Excessive salivation, lacrimation
Nausea, vomiting
Diarrhea
Urinary frequency
Diarrhea
Urinary
Miosis
Bradycardia
Emesis
Lacrimation
Lethargy
Salivation
Myasthenia gravis - clinical examination (4)
The most pertinent findings from neurological examinations were:
Thymectomy scar.
Demonstrate weakness/fatigue in
- Sustained upward gaze weakness - look for the “peek sign” (weakness of orbicularis oculi - close the eyelids, within 30 seconds they will begin to separate, see lower sclera)
- Bulbar muscle weakness (counting, reading loud)
- Proximal weakness (hold arms above head)
- Flap one arm: 10-30 seconds
Dysarthria
chest expansion was normal
“Rest of the neurological examinations were unremarkable”
Myasthenia gravis - investigations?
**_T:_** Tensilon (now replaced by ICE pack test), antibodies to a) ACh receptor, b) MUSK, c) LRP4, d) Antistriated muscle (90% in thymoma), repetitive nerve stimulation + single fibre EMG (repetitive nerve stimulation → progressive reduction in AP amplitude. EMG shows jitter & blocking).
Exclude Eaton-Lambert Myasthenic syndrome - AbS to VGCa channel → if positive investigate for SCLC. Other autoimmune conditions - RhF, ANA, TFT.
MRI/CT to look for thymoma, exclude alternative pathologies, LP to exclude e.g. lymphoma/carcinomatous meningitis.
T: FBC, EUC, LFTs, CRP to look for medication side effects - cytopaenia,hepatitis, infection
Screen for complications: CXR - aspiration pneumonia, monitor lung function tests, DEXA if on steroids…etc.
Management of acute myasthenic crisis? (4)
= life-threatening condition due to neuromuscular respiratory failure
- Involve ICU for anticipatory mechanical ventilation
- Monitor closely with lung function test (vital capacity)
- IVIG or PEX is indicated
- High-dose steroids (e.g. 60-80mg Prednisolone): there is a transient worsening of serious symptoms up to 50% (involve experts) that require intubation up to 10%. Starts around day 5 post steroids - hence important to give IVIG or PEX concurrently
What is your approach to managing this patient with myasthenia gravis?
Goal: minimise symptoms, achieve remission, prevent complications
Confirm Dx: r/v Tensilon/ICE-pack, ACh-R Abs, imaging for thymoma, EMG (progressive drop in AP amplitude, jitter)
A: screen & treat depression, investigate secondary associations - ANA, RhF, TSH (work-up for associated autoimmune conditions). R/o ELS (VG-Ca channel Abs).
S: complications - CXR (pneumonia), LFT/Spirometry (reduction in VC + MIP)
T: Non-pharm
- Education: aim to increase awareness of medications that could worsen symptoms (fluoroquinolones, aminoglycoside, antimalarials), importance of infection prophylaxis
- Infection prophylaxis: vaccinate, hygiene, contacts…etc. Aggressive tx of infection to prevent myasthenia crisis.
- Lifestyle changes: smoking cessation, ETOH (falls), moderate exercise, healthy-balanced diet
- Support groups
T: Pharm
- Acute crisis: ICU, monitor VC, PEX/IVIG + Steroids
- Symptoms: pyridostigmine (acetylcholinesterase)
- Steroids: when still symptomatic despite pyridostigmine (usually req long-term)
- PEX: in acute situations e.g. preparing for surgery, peripartum
- ImmSx: if steroid fails/severe disease - AZA, CsA, MMF
- Rituximab
- Thymectomy if ACh-Ab +ve (70% improves)
- For MUSK disease: ImmSx do not work well. Consider regular PEX. Higher chance of RF, so monitor lung function carefully.
Involve: support groups, neurologist, AH…etc.
Ensure F/U and monitor for symptoms, screen for complications (e.g. steroid/ImmSx/cholinergic toxicity).
What medications must you avoid in patients with Myasthenia? (3)
Fluoroquinolones (e.g. moxi, cipro)
Aminoglycosides (Gent!)
Antimalarials
What is the main differential diagnosis and how would you differentiate it from Myasthenia gravis? (4)
Lambert-Eaton Syndrome.
Associated with SCLC in 50% - so work up as needed.
Power may increase on repeated effort with reduction in reflex
Occular/bulbar muscles are usually spared
EMG: small CMAP but increment on repetitive firing
Ab to VGCa +ve in 80-90% cases
What is the prognosis of myasthenia gravis?
Good - 50% will achieve remission
Although 5-10% die from respiratory failure
What is the implication of Myasthenia for operation and what are you gonna tell the anaesthetist?
Patients with MG are unpredictably resistant or sensitive to many neuromuscular blocking agents.
Approach
- Continuation of MG medications up to the time of surgery
- Use short or ultrashort acting sedatives/agents
- Avoid NM blocking agents
- If NMBA required, use steroidal ones such as Rocuronium/Vecuronium to allow reversal with sugammadex.
How would you monitor this patient with Myasthenia Gravis? (4)
- History and exam: fatiguability, worsening dysphagia, SOB, weakness, diplopia
- AChR titre (Tan says so, not recommended by UTD)
- Spirometry (*** VC and MIP/MEP - Max Inspiratory/Expiratory Pressure) or Peakflow
- Repetitive Nerve Stimulation and EMG
