Myasthenia gravis and neuromuscular junction disorders: Viva

Branch 1: Making the diagnosis

A strong candidate recognises this as autoimmune myasthenia gravis on the clinical picture alone, before the tests return. The diagnosis turns on the fatigability, the fluctuation, and the preservation of the reflexes and the pupils, rather than on a single test. The girl has fluctuating, fatigable weakness of the ocular, bulbar, and proximal muscles that worsens through the day and recovers with rest, the deep tendon reflexes and the pupils are spared, and the ice pack test lifts the ptotic eyelid within two minutes. The antibody panel with the acetylcholine receptor and the muscle-specific kinase antibodies and the repetitive nerve stimulation confirm the diagnosis, but the acetylcholine receptor antibody is negative in around twenty percent of generalised disease, so a negative result never excludes the diagnosis in a typical picture. [1]

Branch 2: Respiratory monitoring and the intensive care decision

When the examiner asks how the candidate monitors the respiratory status, the answer is bedside spirometry every two to six hours in any child with progressive or bulbar weakness, measuring the forced vital capacity, the negative inspiratory force, and the peak cough flow. The intensive care triggers are a forced vital capacity under twenty millilitres per kilogram or a negative inspiratory force under negative forty centimetres of water, and the intubation threshold is a forced vital capacity under fifteen millilitres per kilogram or bulbar weakness with a weak cough and aspiration risk. The candidate stresses that the decision to intubate is driven by the numbers, not by how the child looks, because a child who is still talking in full sentences can have a falling vital capacity, and that a rapid sequence induction is used because the weak respiratory muscles and the aspiration risk make this a high-risk airway. [2]

Branch 3: The treatment ladder

When asked how the candidate runs the ladder, the answer is to secure the airway and breathing first, then layer symptomatic and disease-modifying therapy. Symptomatic first-line therapy is pyridostigmine around one milligram per kilogram per dose four to five times daily, titrated to the response and the cholinergic side effects. Corticosteroids are the mainstay of immunotherapy but are started low, at around half a milligram per kiligram per day and titrated upward, because a high starting dose can transiently worsen the disease and precipitate crisis, and a steroid-sparing agent such as azathioprine, mycophenolate, or methotrexate is added early to permit the steroid taper. For a crisis, intravenous immunoglobulin 2 g per kg over two to five days or plasma exchange three to five sessions over one to two weeks is used, which the Cochrane review found equally effective. The candidate must be crisp on the steroid-start point because examiners ask it directly. [5]

Branch 4: Thymectomy and the refractory disease

The examiner then asks when the candidate would consider thymectomy and the biological agents. The strong candidate states that a thymoma mandates surgical resection in every age group, and that in non-thymomatous generalised acetylcholine receptor antibody disease the MGTX trial showed that extended transsternal thymectomy plus prednisone improved the clinical status over three years, so it is a rational option for this adolescent, while it is not helpful in muscle-specific kinase disease or the congenital syndromes. For refractory anti-acetylcholine receptor generalised disease, eculizumab, a terminal complement inhibitor, is reserved after the REGAIN trial, with meningococcal vaccination and vigilance for meningococcal infection, and rituximab has a particular role in refractory muscle-specific kinase disease. [4]

Branch 5: Distinguishing the congenital myasthenic syndromes

If the examiner changes the picture to an infant with fatigable weakness from birth, a family history, and a negative antibody panel, the candidate recognises a congenital myasthenic syndrome, which is genetic and not antibody-mediated, and confirms the subtype on a neuromuscular gene panel. The candidate names the subtype-specific treatment and the trap: pyridostigmine helps acetylcholine receptor deficiency and the RAPSN syndrome, but it worsens Dok7, ColQ endplate acetylcholinesterase deficiency, and the slow-channel syndrome, which are treated instead with ephedrine, salbutamol, quinidine, or fluoxetine. The candidate distinguishes the maternal antibody syndromes: transient neonatal myasthenia resolves over weeks, while fetal acetylcholine receptor inactivation syndrome causes arthrogryposis and a permanent myopathy. [9]

Branch 6: Prognosis and the family

Asked what to tell the family, the candidate quotes that children with autoimmune myasthenia gravis have a good prognosis when well managed, with many achieving pharmacological remission on low-dose immunotherapy, and that the ocular-only form often remits. The candidate is honest that the course is chronic and relapsing, that around fifteen to twenty percent of children will have a crisis commonest in the first year, and that the corticosteroids carry the growth, weight, and bone side effects that need monitoring. The candidate gives the family a written school and crisis plan with a safety-net for a falling forced vital capacity, arranges paediatric neurology follow-up, and plans a structured transition to adult care. The myasthenia gravis Foundation of America classification tiers the severity and the post-intervention status. [2]

The examiner rewards a candidate who measures the forced vital capacity, who starts the corticosteroids low, who confirms the antibody or the gene before committing to pyridostigmine, who times the thymectomy and the biological agents, and who quotes the paediatric prognosis honestly. [1]