Long-term Management of Idiopathic Cough with Ultrasound-Guided Pulsed Radiofrequency Ablation of the Phrenic Nerve
Idiopathic cough, characterized by its association with laryngeal hypersensitivity and chronic pain syndromes, poses significant challenges in clinical management. This condition is diagnosed when no identifiable cause of chronic cough persists after standard treatments. Patients suffering from idiopathic cough often experience a diminished quality of life (QOL), disruptions in daily activities, and psychological distress such as depression. Given the profound impact on patients’ lives, there is a pressing need for innovative and effective treatment strategies for refractory chronic cough.
The phrenic nerve, originating from the ventral rami of the cervical nerve roots (C3-5), plays a critical role in diaphragmatic function. It provides motor innervation to each hemidiaphragm, making it a pivotal structure in respiratory mechanics. Recent advancements in pain management techniques have explored the potential of targeting the phrenic nerve to alleviate symptoms associated with idiopathic cough.
This article presents a detailed account of the use of ultrasound-guided pulsed radiofrequency (PRF) ablation of the phrenic nerve in managing idiopathic cough in patients who did not respond to conventional drug therapies. The procedure was performed on two female patients, aged 57 and 55, who had been suffering from idiopathic cough for 8 and 20 years, respectively. Both patients had undergone extensive diagnostic evaluations, including bronchoscopy, esophagogastroduodenoscopy, pulmonary function tests, and chest X-rays, all of which yielded normal findings. Despite these assessments and subsequent treatments from the respiratory medicine department, their symptoms remained unmanaged.
The initial approach involved ultrasound-guided phrenic nerve block (PNB) using 5 mL of 0.4% lidocaine. The first patient, a 57-year-old female with Graves’ disease, experienced a 50% reduction in the intensity and frequency of her daily cough following a left-sided PNB. A subsequent right-sided PNB performed four days later resulted in a 90% relief of symptoms. To maintain symptom control, PNBs were administered weekly for two weeks and then monthly for six months. The patient reported no side effects, and there were no changes in chest imaging or related laboratory tests. However, during the final block, the patient exhibited seizure-like activity, prompting a shift to PRF ablation of the phrenic nerve.
The PRF procedure was conducted with the patient in the supine position under aseptic conditions. Test stimulation was performed at 2 Hz and 0.5 mA, followed by PRF at 42°C for 120 seconds, repeated for three cycles. The patient experienced significant relief from cough symptoms for six months, after which the procedure was repeated on the left side using the same method. The second patient, a 55-year-old female with a 20-year history of chronic refractory cough, underwent a similar treatment protocol. Initial right-sided PNB reduced her cough frequency and duration by 50%. Weekly alternating PNBs for a month further reduced the intensity and frequency of daily cough by 30%. Subsequently, PRF ablation of the phrenic nerve was performed, leading to effective symptom management at a three-month follow-up.
The underlying mechanisms of PNB and PRF in treating idiopathic cough remain incompletely understood. However, studies have suggested a relationship between phrenic nerve activity and the cough reflex. Research conducted on anesthetized dogs demonstrated increased phrenic nerve discharge activity, spike potential amplitude, and pulse density during the cough reflex. It is hypothesized that PRF ablation of the phrenic nerve may inhibit the evoked synaptic activity of excitatory C-fibers in response to repetitive, burst-like stimulation of Aδ-fibers, thereby altering nerve tissue structure and reducing phrenic nerve activity. This reduction in nerve activity could potentially alleviate idiopathic cough without causing significant complications.
In conclusion, ultrasound-guided PRF ablation of the phrenic nerve emerges as a safe and effective intervention for the long-term management of idiopathic cough. The procedure offers significant symptom relief and improves patients’ quality of life, as evidenced by the case studies presented. Nonetheless, further research is warranted to elucidate the precise mechanisms underlying this treatment modality and to optimize its application in clinical practice.
doi.org/10.1097/CM9.0000000000001993
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