MEDizzy - A 66-year-old man presents to the emergency department

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Combined Neurology XII

A 66-year-old man presents to the emergency department complaining of a 2-week history of marked slurring of speech, difficulty swallowing, and trouble holding his head up. He had been diagnosed with myasthenia gravis 2 years earlier, but symptoms had only included diplopia up until he had a flu-like illness 2 weeks earlier. On examination, he has bilateral ptosis and severe dysarthria. He cannot hold his head up off the bed when supine. He is tachypneic and is using accessory muscles to breathe. His negative inspiratory force is −15 cm H2O. What is the most appropriate next step in the management of this patient?

ExplanationD. The patient depicted is presenting in myasthenic crisis. In patients with signs of respiratory muscle involvement, negative inspiratory force and forced vital capacity should be monitored closely. Intubation and mechanical ventilation should be initiated when the negative inspiratory force is less than −30 cm of H2O, forced vital capacity less than 15 mL/kg, or if there is a significant downward trend of spirometry measures with clinical evidence of respiratory muscle fatigue. The patient should be admitted to the ICU and intubated and mechanically ventilated. In patients with significant oculobulbar symptoms, neck flexor weakness (suggesting potential involvement of respiratory muscles), or respiratory muscle weakness, initial treatment is with either intravenous immunoglobulins (IVIGs) or plasmapheresis. Higher efficacy of one modality over the other has not been established and both are reasonable options. One is chosen over the other based on availability, cost, underlying medical conditions, or previous response. Medications that exacerbate myasthenia gravis include aminoglycosides, β-blockers, and neuromuscular blocking agents, among others. These should be avoided or used at the lowest possible dose in myasthenia gravis; symptom exacerbation with initiation of any medication should prompt investigation as to whether or not the medication is the culprit. Penicillamine can cause a seropositive myasthenic syndrome. The majority of patients with myasthenia gravis, except some with purely ocular myasthenia, require immunosuppressive therapy. Patients are often treated with corticosteroids for several weeks to months until secondary immunosuppressive therapy has taken effect. Approximately one-third of patients will have worsening of their myasthenic symptoms at the onset of steroid therapy that lasts up to 10 days. Therefore, caution is required with the initiation of steroid therapy. When symptoms are severe, and there is concern for significant pharyngeal or respiratory muscle involvement, initiation of plasma exchange or IVIGs prior to starting corticosteroids may be necessary. Secondary immunosuppressive agents that may be used include azathioprine, mycophenolate mofetil, cyclophosphamide, and cyclosporine. Their use helps reduce the need for steroids in the long term. Pyridostigmine provides symptomatic relief but does not modify the course of the illness. In the majority of patients with autoimmune myasthenia gravis, thymic abnormalities are present, most commonly lymphoid follicular hyperplasia. In a minority of patients, benign thymoma is present, and rarely, malignant thymoma. Resection of the thymus (regardless of whether or not thymoma is present) can potentially induce remission of myasthenia gravis. In autoimmune myasthenia gravis, there are ongoing clinical trials to determine the utility of thymectomy. However, there is evidence that patients who undergo thymectomy are more likely to attain remission of their myasthenia gravis. Thymectomy is therefore recommended for patients with myasthenia gravis with symptom onset prior to the age of 60, especially in younger women who seem to show the most benefit. Response to resection may not be apparent for several months to years. Because myasthenic symptoms can worsen in the perioperative period, stabilization of symptoms with preoperative IVIGs or plasma exchange prior to operation may be indicated.