Myasthenia gravis and neuromuscular junction disorders

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Target exams

Red flags

• Fatigable weakness that worsens with repeated activity and recovers with rest, affecting the ocular, bulbar, and proximal limb muscles, is myasthenia gravis until proven otherwise
• Measure bedside forced vital capacity every two to six hours; a value under fifteen millilitres per kilogram, a negative inspiratory force under negative forty centimetres of water, or a weak cough with pooled secretions mandates intubation
• MuSK antibody myasthenia gravis presents with prominent bulbar, facial, and respiratory weakness, responds poorly to acetylcholinesterase inhibitors, and is more likely to progress to crisis
• Starting corticosteroids at a high dose can transiently worsen myasthenia gravis and precipitate crisis; begin prednisolone low and titrate upward with concurrent immunotherapy
• Pyridostigmine worsens several congenital myasthenic syndromes including Dok7, endplate acetylcholinesterase deficiency, and the slow-channel syndrome; confirm the subtype before treating
• A baby of a myasthenia gravis mother with arthrogryposis and fixed weakness at birth has fetal acetylcholine receptor inactivation syndrome, which is permanent and not transient neonatal myasthenia

Life stages

Care settings

Clinical exam formats

Board mappings

• Recognises that fatigable weakness of the ocular, bulbar, and proximal limb muscles that worsens with repeated activity and recovers with rest is myasthenia gravis
• States that pyridostigmine is the symptomatic first-line agent and that intravenous immunoglobulin 2 g per kg over two to five days treats a myasthenic crisis
• Identifies the respiratory red flags of a falling forced vital capacity and bulbar weakness and the need for intensive care monitoring
• Distinguishes the acetylcholine receptor, muscle-specific kinase, and LRP4 antibody subtypes and the congenital myasthenic syndromes, and explains why pyridostigmine worsens Dok7, endplate acetylcholinesterase deficiency, and the slow-channel syndrome
• Justifies the timing of thymectomy using the MGTX trial and the choice of eculizumab for refractory anti-acetylcholine receptor disease using the REGAIN trial
• Applies the myasthenia gravis Foundation of America classification, the bedside fatiguability manoeuvres, the ice pack test, and the repetitive nerve stimulation and single-fibre neurophysiology
• The autoimmune versus congenital and the presynaptic versus synaptic versus postsynaptic classification, and the acetylcholine receptor, muscle-specific kinase, and LRP4 antibody signatures
• Pyridostigmine dosing, the corticosteroid transient worsening, the intravenous immunoglobulin and plasma exchange for crisis, thymectomy, and eculizumab
• The respiratory monitoring thresholds and the subtype-specific treatment of the congenital myasthenic syndromes
• Runs the assessment, respiratory monitoring, and treatment ladder of a child with fatigable weakness while excluding the mimics
• Decides on and times intensive care escalation using forced vital capacity and bulbar monitoring, and manages a myasthenic crisis with intravenous immunoglobulin or plasma exchange
• Counsels the family on the chronic relapsing course, the medication side effects, the thymectomy decision, and the transition to adult care
• Level 1: Recognition that fatigable, fluctuating weakness of the ocular, bulbar, and proximal muscles that recovers with rest is a neuromuscular junction disorder until proven otherwise
• Level 2: Application of the antibody panels and neurophysiology, pyridostigmine dosing, and the respiratory monitoring with forced vital capacity thresholds
• Level 3: Distinction of the congenital myasthenic syndromes and the maternal antibody syndromes, the management of crisis, and the coordination of long-term immunotherapy and rehabilitation
• Myasthenia gravis as an antibody-mediated attack on the neuromuscular junction with fatigable weakness, and the acetylcholine receptor and muscle-specific kinase antibody subtypes
• Pyridostigmine as symptomatic therapy, corticosteroids and steroid-sparing agents, intravenous immunoglobulin and plasma exchange for crisis, and thymectomy
• The congenital myasthenic syndromes as genetic disorders with subtype-specific treatment, and the distinction from transient neonatal myasthenia
• Structured assessment of a child with fatigable weakness using sustained-upgaze, the ice pack test, and bedside spirometry
• Recognition of intensive care triggers and the timing of intravenous immunoglobulin, and the exclusion of the mimics
• Communication of the chronic relapsing diagnosis, the medication plan, and the transition pathway to the family
• Juvenile myasthenia gravis as the common paediatric autoimmune neuromuscular junction disorder with acetylcholine receptor antibodies and a predilection for adolescent girls
• Pyridostigmine first-line, intravenous immunoglobulin 2 g per kg over two to five days for crisis, and thymectomy for thymoma and selected seropositive disease
• The congenital myasthenic syndromes and the distinction between the antibody-mediated and the genetic disorders, including the subtypes worsened by pyridostigmine
• Recognition of fatigable, fluctuating weakness as a neuromuscular junction disorder and the exclusion of the mimics
• Stepwise management with symptomatic therapy, immunotherapy, respiratory monitoring, and intensive care escalation for crisis
• Multidisciplinary care of the chronic relapsing course, the medication side effects, and the transition to adult care
• Canadian approach to the diagnosis and classification of myasthenia gravis using the antibody panels and neurophysiology
• Pyridostigmine, immunotherapy, intravenous immunoglobulin and plasma exchange for crisis, and thymectomy after the MGTX trial
• Coordination of long-term immunotherapy, the congenital myasthenic syndromes, and the maternal antibody syndromes