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Myasthenia Gravis

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🔗 Related Subjects: | 💪 Myasthenia Gravis | ⚡ Lambert-Eaton syndrome (LEMS)

😴 Fluctuating, fatigable muscle weakness of eye, bulbar, respiratory, and limb muscles.

🚨 Initial Management of Myasthenic Crisis
🫁 Exhaustion, poor respiratory effort, weak cough, cyanosis, low FVC. 😮 Dysphagia, dysarthria, dyspnoea, diplopia. ⚠️ Crisis may be due to MG or excess anticholinesterases → involve ITU early. 🩺 ABC approach: intubation + ventilation, stop all MG drugs initially. 💉 Edrophonium chloride (2 mg IV) may transiently improve symptoms. 🩸 If worsening MG: plasma exchange (PLEX) or IV immunoglobulins (IVIg). 🚫 Avoid: penicillamine, aminoglycosides, tetracyclines, phenytoin.

🚨 Initial Management of Myasthenic Crisis

🫁 Exhaustion, poor respiratory effort, weak cough, cyanosis, low FVC.
😮 Dysphagia, dysarthria, dyspnoea, diplopia.
⚠️ Crisis may be due to MG or excess anticholinesterases → involve ITU early.
🩺 ABC approach: intubation + ventilation, stop all MG drugs initially.
💉 Edrophonium chloride (2 mg IV) may transiently improve symptoms.
🩸 If worsening MG: plasma exchange (PLEX) or IV immunoglobulins (IVIg).
🚫 Avoid: penicillamine, aminoglycosides, tetracyclines, phenytoin.

📖 About

🧬 Myasthenia Gravis (MG) is an autoimmune disorder where antibodies target nicotinic acetylcholine receptors, causing fatigable weakness.

🧪 Aetiology

🔑 90% have anti-AChR antibodies.
🦠 Anti-MuSK antibodies in some AChR-negative patients.
🏹 Anti-Titin & anti-RyR often seen with thymomas.
🧨 Pathology: complement-mediated damage → ↓ ACh receptors → impaired neuromuscular transmission.

🔗 Clinical Associations

🦋 Autoimmune: RA, SLE, Sjögren’s, sarcoidosis.
🩸 Haematological: pernicious anaemia.
🧩 Others: polymyositis, ulcerative colitis, pemphigus.

🧩 Clinical Features

♻️ Fluctuating weakness worsens with activity (fatigability).
👀 Ocular: diplopia, ptosis (pupil spared).
👁️ Cogan’s lid twitch: classic eyelid sign.
🫁 Respiratory: may lead to crisis with failure.
🍽️ Bulbar: dysphagia, dysarthria, chewing difficulty, abnormal smile.
⚠️ Myasthenic crisis: severe respiratory muscle weakness → urgent PLEX/IVIg.
🤰 Pregnancy: symptoms often worsen in 1st trimester; neonatal MG possible.

🧾 Differential Diagnosis

⚡ Lambert-Eaton Myasthenic Syndrome (LEMS).
☠️ Botulism.
💊 Drug-induced (penicillamine, aminoglycosides).
🧿 Chronic Progressive External Ophthalmoplegia (CPEO).

🔎 Investigations

🧪 Anti-AChR antibodies (90%).
🧪 Anti-MuSK if AChR negative.
⚡ Neurophysiology: RNS or SFEMG → impaired transmission.
💉 Tensilon (edrophonium) test → transient improvement.
🧊 Ice pack test → improves ptosis.
🫀 Chest CT/MRI → thymoma screening.
🦋 TFTs → check for thyroid disease.

❓ Key Diagnostic Questions

Is the patient AChR or MuSK seropositive/seronegative?
Is a thymoma present?
Ocular or generalised symptoms?
Could this be congenital MG?

🚫 Drugs to Avoid in MG

Drug	Mechanism
💊 Aminoglycosides, Phenytoin, Lignocaine, Beta-blockers, Quinidine	↓ ACh release at neuromuscular junction
💊 Penicillamine	Induces AChR antibodies
💊 Lithium	Causes MG-like weakness

💊 Medications in MG

🛠️ Management

💊 Pyridostigmine: 30–60 mg PO q4h; adjust to symptoms.
🧴 Prednisolone: dose escalation; esp. effective in MuSK+ disease.
🧬 Immunosuppressants: azathioprine, mycophenolate, methotrexate, cyclosporine.
🧪 Refractory MG: IVIg, plasmapheresis, rituximab.
🔪 Thymectomy: for all MG with thymoma; improves long-term disease control.
🚑 Crisis: IVIg or plasmapheresis urgently.
🤰 Pregnancy: pyridostigmine safe; steroids if required; avoid teratogenic immunosuppressants.
🚫 Avoid MG-worsening drugs (aminoglycosides, tetracyclines, phenytoin, penicillamine).

📚 References

Cases — Myasthenia Gravis (MG)

Case 1 — Ocular Myasthenia 👁️: A 28-year-old woman reports drooping of her right eyelid that worsens by evening and double vision after prolonged reading. Exam: fatigable ptosis and ophthalmoparesis. No limb weakness. Diagnosis: Ocular myasthenia gravis. Management: Pyridostigmine (acetylcholinesterase inhibitor); monitor for progression to generalised MG; immunosuppressants if refractory.
Case 2 — Generalised MG with Bulbar Symptoms 🗣️: A 45-year-old man presents with fluctuating limb weakness, nasal speech, and difficulty swallowing, especially late in the day. Exam: fatigable proximal weakness, weak neck flexion, and reduced palatal movement. Diagnosis: Generalised MG with bulbar involvement. Management: Pyridostigmine; immunosuppression (prednisolone, azathioprine); screen for thymoma with CT chest; MDT support (speech and physio).
Case 3 — Myasthenic Crisis in ICU ⚠️: A 52-year-old woman with known MG develops pneumonia and acute worsening weakness, now with difficulty speaking and shallow breathing. Exam: weak cough, reduced vital capacity. Diagnosis: Myasthenic crisis precipitated by infection. Management: Admit to ICU; ventilatory support if needed; IV immunoglobulin or plasma exchange; optimise infection treatment; adjust long-term immunotherapy.

Teaching Commentary 🧠

Myasthenia gravis is an autoimmune disorder of the neuromuscular junction, usually due to antibodies against the ACh receptor (AChR) or MuSK. Hallmarks: fluctuating, fatigable weakness, classically ocular (ptosis, diplopia), bulbar (dysarthria, dysphagia), and proximal limb/neck. Reflexes and sensation remain intact. Red flags: myasthenic crisis with respiratory weakness — life-threatening. Dx: AChR/MuSK antibodies, EMG (decrement on repetitive stimulation), CT chest (thymoma). Rx: Pyridostigmine, steroids/immunosuppressants, IVIG/plasma exchange for crisis, thymectomy if thymoma. Avoid drugs that worsen MG (aminoglycosides, beta-blockers, magnesium).

PLEASE NOTE LEGAL ADVICE: The contents are under continuing development and improvements and may contain errors of omission or fact. Feedback vital and always welcome at drokane at gmail.com. This is not to be used for the assessment, diagnosis or management of patients. It should not be regarded as medical advice. It is only for educational purposes. Please adhere to your local protocols. If you are unwell please seek healthcare advice from your doctor. This does not replace senior or specialist advice. If you do not accept this then please do not use the website. If you need medical advice, please consult a doctor or other appropriate medical professional. If you are a medical professional and you need advice then speak to your senior or colleagues.

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