Dyspnea of Unknown Cause—Don’t Discount Diaphragm Dysfunction

By Matthew Gordon, MD

Respiratory muscle dysfunction, especially diaphragm dysfunction, is a well-documented but often-overlooked source of dyspnea. Etiologies of diaphragm dysfunction are myriad, ranging from metabolic derangements, central and peripheral neurologic conditions, anatomic changes, and trauma; it can also be a sequela of prolonged mechanical ventilation.

Abdominal Paradox: During inspiration, a functional diaphragm will move caudally, increasing abdominal pressure and causing outward motion that corresponds with rib cage expansion (A). With paralysis, the diaphragm will move cranially, with a paradoxical inward motion of the abdomen as the rib cage expands (B). This paradoxical breathing pattern is most easily observed in the supine position.

Dysfunction of the diaphragm ranges from weakness to complete paralysis, either unilaterally or bilaterally. Unilateral paralysis may result in decreased exercise capacity and dyspnea on exertion. Symptoms are often worse in the supine position and can be associated with sleep disordered breathing. Bilateral diaphragm dysfunction presents with severe dyspnea, often occurring at rest, and is frequently accompanied by respiratory failure.

Both diagnostic and therapeutic interventions are available, but are often difficult to obtain, interpret, and adequately assess, especially during sleep. While an excellent screening tool, chest X-rays are an insensitive test for diaphragm dysfunction. Continuous fluoroscopy with a “sniff maneuver” can diagnose unilateral paralysis but is not a useful exam to assess for bilateral dysfunction. Diaphragm ultrasound is an emerging method to assess function of the diaphragm. Non-invasive and without radiation exposure, ultrasound can detect muscle contraction, and is applicable for both uni- and bilateral diaphragm dysfunction, as well as trend response to therapy.

Diaphragm dysfunction rarely occurs in isolation, and determining its contribution to dyspnea through positional spirometry, imaging, measurement of trans-diaphragmatic pressures and response to nerve stimulation is crucial to develop a patient-centered treatment plan.

Interventions, both surgical and non-surgical, can improve respiratory status, exercise and sleep performance, and overall quality of life, and may free some patients from mechanical ventilation. Optimizing nutrition and correcting metabolic derangements, combined with physical rehabilitation and inspiratory muscle training, can speed recovery of patients with diaphragm dysfunction or unilateral paralysis. Non-invasive ventilation can ameliorate symptoms and delay the need for mechanical ventilation. Surgically, plication of the diaphragm can eliminate paradoxical motion, increase lung volumes, and decrease symptoms in select patients with unilateral paralysis. For those with bilateral diaphragm paralysis, multiple surgical techniques can provide external electrical stimulation to the phrenic nerve in order to stimulate muscle contraction. Pacing of the diaphragm can liberate patients with high-cervical injuries from the ventilator, significantly improving quality of life.

Diagnosis and management of patients with respiratory muscle weakness requires a comprehensive, multidisciplinary approach. A variety of diagnostic and treatment modalities are available to provide a patient-centered treatment plan focused on improving quality of life.