A 32-year-old woman presents to the neurology clinic with progressive muscle weakness, ptosis, and diplopia that worsens toward the end of the day. Antibody testing confirms seropositivity for acetylcholine receptor (AChR) antibodies. She is started on pyridostigmine, but symptoms persist despite adequate dosing. What is the most appropriate next step in management?

Explanation

## Clinical Context: Myasthenia Gravis (MG) Management This patient has seropositive MG (AChR antibodies present) with inadequate response to anticholinesterase monotherapy. The next step is immunosuppression. ### Pathophysiology of Synaptic Failure in MG **Key Point:** In MG, autoantibodies bind to AChR at the neuromuscular junction, causing complement-mediated destruction and reduced acetylcholine binding capacity. Anticholinesterases alone prolong ACh availability but do not address the underlying autoimmune destruction. ### Management Algorithm for Seropositive MG ```mermaid flowchart TD A[Seropositive MG confirmed]:::outcome --> B[Start pyridostigmine]:::action B --> C{Adequate symptom control?}:::decision C -->|Yes| D[Continue + monitor]:::action C -->|No| E[Add immunosuppression]:::action E --> F[Prednisolone + Azathioprine]:::action F --> G[Consider IVIG/plasmapheresis if crisis]:::action ``` ### Treatment Hierarchy in MG | Stage | Intervention | Indication | |-------|---|---| | **First-line** | Pyridostigmine | All patients; symptomatic relief | | **Second-line** | Immunosuppression (prednisolone ± azathioprine) | Inadequate response to anticholinesterase monotherapy | | **Third-line** | Plasmapheresis / IVIG | Myasthenic crisis, pre-operative preparation, acute exacerbation | | **Definitive** | Thymectomy | Thymoma present or generalized MG | **High-Yield:** Prednisolone is the cornerstone of immunosuppression in MG. Azathioprine is added as a steroid-sparing agent to allow dose reduction and minimize long-term corticosteroid toxicity. **Clinical Pearl:** Immunosuppressive therapy typically requires 6–12 weeks to show benefit; anticholinesterases provide immediate symptomatic relief while waiting for immune modulation to take effect. ### Why Immunosuppression Now? 1. **Inadequate pyridostigmine response** = evidence of ongoing autoimmune destruction 2. **Seropositive status** = confirmed antibody-mediated disease (not seronegative MG, which may have different kinetics) 3. **Stable, non-crisis state** = appropriate timing for slower-acting immunosuppressants [cite:Harrison 21e Ch 382]