A 52-year-old man with progressive bulbar dysarthria and limb weakness presents with dyspnea on exertion. Spirometry shows FVC 45% predicted with normal DLCO. The structure marked **C** in the diagram (Reduced MIP/MEP) is found to be severely impaired on respiratory muscle testing. Which of the following is the most appropriate next step in management?

Explanation

## Why "Initiate non-invasive ventilation (BiPAP) with serial monitoring of FVC and MIP" is right The patient presents with ALS (bulbar dysarthria + progressive weakness) with neuromuscular respiratory weakness evidenced by reduced MIP/MEP (marked **C**), FVC 45% predicted, and preserved DLCO. According to Harrison 21e Ch 287, NIV (BiPAP) is the standard of care for symptomatic neuromuscular respiratory insufficiency when MIP < −60 cm H₂O or FVC < 50% predicted. NIV improves survival, quality of life, and dyspnea in ALS patients. Serial FVC and MIP monitoring guides escalation to mechanical ventilation only if rapid decline occurs (>30% within 12 hours) or if MIP/MEP drop below critical thresholds (<30 cm H₂O). This approach preserves patient autonomy and allows time for advance care planning. ## Why each distractor is wrong - **Perform immediate endotracheal intubation and mechanical ventilation**: Intubation is reserved for acute respiratory failure (FVC <20 mL/kg, MIP <30 cm H₂O, or rapid decline >30% in 12 hours). At FVC 45% with stable presentation, NIV is first-line. Premature intubation commits the patient to tracheostomy and mechanical ventilation without trial of less invasive support. - **Start high-dose corticosteroids and immunosuppressive therapy**: This approach is appropriate for myasthenia gravis or inflammatory myopathies, not ALS. The clinical picture (bulbar onset, progressive motor neuron signs) and preserved DLCO are inconsistent with myasthenia or myositis. Steroids have no disease-modifying role in ALS. - **Refer for diaphragm pacing and surgical intervention**: Diaphragm pacing is reserved for high cervical spinal cord injury (C3–C5) or congenital central hypoventilation syndrome (PHOX2B mutation), not for ALS. It is not a standard intervention for neuromuscular diseases affecting the motor neuron or muscle itself. **High-Yield:** In neuromuscular restrictive patterns with preserved DLCO and reduced MIP/MEP, NIV is initiated when symptomatic with MIP < −60 cm H₂O or FVC < 50%; intubation thresholds are MIP < −30 cm H₂O, FVC < 20 mL/kg, or rapid decline >30% in 12 hours. [cite: Harrison 21e Ch 287; Neuromuscular Disorders and Respiratory Failure]