Neurology · MU Sofia

80. Myasthenia gravis, congenital myasthenic syndromes

Covers myasthenia gravis as an autoimmune neuromuscular junction disorder, moving through antibody targets and associated thymic conditions, pathogenesis, clinical features from ocular and bulbar to respiratory involvement, examination, diagnostic tests including single-fiber EMG and chest imaging, treatment options, and myasthenic crisis. It then describes congenital myasthenic syndromes, their inherited basis, genetic subtypes, contrasting antibody-negative diagnosis, subtype-based treatment, and a differential diagnosis list naming Lambert–Eaton syndrome, muscular dystrophy and motor neuron disease.

Inside: 3 sections · 1 labelled picture · 15 flashcards · 2 min

Topic 80 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 3 sections, about 303 words (2 min of reading), with 15 flashcards.

In this note

  1. Myasthenia gravis. Congenital myasthenic syndromes
  2. Myasthenia Gravis (MG)
  3. Congenital Myasthenic Syndromes (CMS)

Myasthenia Gravis (MG)

Definition: Myasthenia Gravis is an autoimmune disease of the neuromuscular junction characterized by fluctuating skeletal muscle weakness and fatigability due to impaired neuromuscular transmission.

Etiology

1.Autoantibodies Against: Acetylcholine receptor (AChR) (most common). Muscle-specific kinase (MuSK). LRP4 (rare)

2.Associated Conditions: Thymic hyperplasia. Thymoma slow-growing tumor that forms on the outside of the thymus gland

Pathogenesis

Autoantibodies destroy or block postsynaptic ACh receptors → ↓ Neuromuscular transmission → Muscle weakness that worsens with activity and improves with rest.

Clinical Features

Hallmark: Fluctuating fatigable weakness

Ocular Symptoms (Most Common Initial Presentation): Ptosis. Diplopia

Bulbar Symptoms: Dysarthria. Dysphagia. Nasal speech. Difficulty chewing.

Limb Weakness: Proximal muscles affected more than distal. Arms often affected before legs

Respiratory Involvement: Respiratory muscle weakness. Myasthenic crisis

Examination

Findings: Fatigability on repeated movements. Ptosis increases with sustained upward gaze. Normal sensation. Normal reflexes

Diagnosis

  • Serology: Anti-AChR antibodies. Anti-MuSK antibodies. Electrophysiology
  • Repetitive Nerve Stimulation: Decremental response
  • Single-Fiber EMG: Most sensitive test. Increased jitter
  • Imaging
  • CT/MRI chest: Detect thymoma

Treatment

Symptomatic: Pyridostigmine (AChE inhibitor)

Immunotherapy: Corticosteroids. Azathioprine. Mycophenolate

Rapid Treatment: Plasmapheresis. IVIG

Surgical: Thymectomy (especially thymoma)

Myasthenic Crisis

Definition: Life-threatening respiratory weakness requiring urgent treatment.

Management: ICU monitoring. Ventilatory support. IVIG or plasmapheresis

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