Introduction

In this article, we present a case that serves to generate hypotheses regarding ultrasound-guided bilateral vagus nerve hydrodissection, combined with pulsed radiofrequency neuromodulation, in a patient with chronic refractory pain in the context of fibromyalgia and ankylosing spondylitis.

Fibromyalgia is a chronic condition characterized by widespread musculoskeletal pain that is primarily associated with sleep disturbances and fatigue. Globally, fibromyalgia is the third most common musculoskeletal condition, after low back pain and osteoarthritis (1). Estimated to affect between 2 % and 6% of the general population, with peak prevalence between the ages of 50 and 60, it predominantly affects women, with a 3:1 female-to-male ratio (1,2).

It is in these patients that we primarily find generalized chronic pain that can become intractable, especially in the musculoskeletal system, without visible manifestations (nociplastic pain).

Chronic pain is defined as pain that persists for more than 3 months; regarding intractable chronic pain, patients describe their pain as constant, debilitating, and severe enough to interfere with sleep and sexual function. Many report suicidal thoughts with the sole purpose of stopping the pain, episodes of incessant crying, fatigue, depression, social isolation, restricted mobility, and numerous days spent in bed; we find that various interventions to control their pain have failed, including surgery, nerve blocks, physical rehabilitation, and weak opioids (3).

The vagus nerve plays a central role in regulating the autonomic nervous system, particularly in modulating sympathetic and parasympathetic tone. Its stimulation has been shown to reduce systemic inflammation via the anti-inflammatory cholinergic pathway, as well as to modulate pain perception through connections with the nucleus of the solitary tract and the limbic system (4).

Impaired vagal conduction, whether due to compression, fibrosis, or inflammation, may contribute to dysautonomic states and the perpetuation of certain pain syndromes, such as chronic visceral pain, migraines, fibromyalgia, and functional gastrointestinal disorders (5). However, interventional approaches targeting the vagus nerve remain understudied in nociplast pain.

An emerging technique is ultrasound-guided hydrodissection of the vagus nerve, which involves the perineural injection of solutions such as 5 % dextrose to release adhesions and restore neural mobility and function. This technique has demonstrated clinical benefits in peripheral neuropathies such as occipital neuralgia and carpal tunnel syndrome, diabetic neuropathy, multisite pain, and nonspecific polyneuropathy (6,7). The carotid sheath, which contains the common carotid artery, the internal jugular vein, and the vagus nerve, serves as a clear anatomical landmark that facilitates precise needle placement. The technique involves accessing the vagus nerve at the level of the C6-C7 vertebrae via hydrodissection, carefully separating it from the carotid artery and surrounding it with a 5 % dextrose solution, without the use of local anesthetics. The use of ultrasound allows the procedure to be performed with high precision and safety, significantly reducing the risk of complications (6).

The objective of this report is to describe the technical feasibility and short-term clinical outcome of ultrasound-guided bilateral vagus nerve hydrodissection, combined with pulsed radiofrequency, in a patient with refractory chronic pain and autonomic and nociceptive features.

Case presentation

A 21-year-old woman presented for consultation with a one-year history of intense, persistent, and diffuse musculoskeletal pain primarily affecting the lumbar, cervical, and thoracic regions, associated with fatigue and functional limitation.

Magnetic resonance imaging revealed no structural abnormalities to explain the pain. Laboratory tests showed elevated inflammatory markers, and rheumatological evaluation led to a diagnosis of ankylosing spondylitis. Despite treatment with opioids, corticosteroids, ketamine infusions, and multidisciplinary care including psychiatry and rehabilitation, the patient developed refractory pain with significant functional impairment.

Given the failure of multimodal therapy, an interventional approach targeting the vagus nerve was considered. Written informed consent was obtained for both the intervention and publication, and the procedure was performed following a multidisciplinary evaluation.

Bilateral hydrodissection plus ultrasound-guided pulsed radiofrequency neuromodulation of the vagus nerve was performed using 5 % dextrose. Pain and functional outcomes were assessed using the Numerical Rating Scale (NRS), the Revised Fibromyalgia Impact Questionnaire (FIQR), and the Bath Ankylosing Spondylitis Functional Index (BASFI).

Pain intensity at baseline was 9–10/10 on the NRS; it decreased to 2/10 immediately after the procedure and remained improved at 3 months (4/10) and 6 months (5/10).

FIQR scores improved from 72 at baseline to 42 at 3 months and to 48 at 6 months, representing a reduction of more than 20 points and exceeding the minimum clinically important difference, supporting a clinically significant improvement.

BASFI scores improved from 8.2 to 5.6, indicating a clinically relevant reduction in symptom burden.

Technique

Equipment and monitoring

The procedure was performed in a single session, bilaterally.

SonoSite PX© ultrasound system and 6–12 MHz linear transducer. 20-G echogenic radiofrequency cannula, 100 mm, 10 mm curved active tip EVA©, ultrasound sleeve with sterile EVA© gel, 1 % lidocaine, 5 cm 27 G hypodermic needle, 5 % dextrose, Boston Scientific G4 RF generator, ASA monitoring, cardiopulmonary resuscitation equipment.

Step 1. Patient positioning: patient in supine or lateral decubitus position, with the neck in hyperextension and slightly rotated contralateral to the approach site. Oxygen via nasal cannula at 1 to 2 L/min and conscious sedation consisting of midazolam at a dose of 0.1 mg/kg combined with sufentanil at 0.05 µg/kg. The objective was to achieve a Richmond Agitation-Sedation Scale (RASS) score between -1 and -2, ensuring mild anxiolysis and light analgesia while preserving patient responsiveness.

Step 2. Identify C7. Using a 12 MHz linear transducer in a transverse position over the neck, identify the seventh cervical vertebra (C7) (Figure 1).

Step 3. Move the transducer cephalad in the same position until C6 is identified, which is characterized by a prominent anterior tubercle. This is the point where the puncture should be made. The key structure to identify is the carotid sheath, which houses the vagus nerve (Figure 2).

Step 4. Optimize the entry path. To perform a successful approach, move the anterior tubercle to the edge of the ultrasound screen; this prevents bony contact. Administer local anesthetic at the access point, then enter with a 22-G echogenic needle or a 22-G RF cannula with a curved, echogenic tip. Once the carotid sheath is reached, hydrodissection of the vagus nerve is performed at this point.

Step 5. Hydrodissection. Once the needle is positioned at the target site, 5 % dextrose solution (5 to 10 mL) is administered slowly but continuously at an approximate rate of 1 mL per minute, resulting in a total administration time of approximately 5 minutes for the full volume, while constantly monitoring vital signs. If bradycardia occurs, administration of the dextrose solution must be suspended, and 500 mcg of atropine must be administered IV (Figure 3). The neuromodulation protocol; the parameters used were 55 V, 42°C, 8 minutes duration, and a discharge frequency of 5 Hz, with a discharge duration of 8 ms (Figure 3).

Step 6. Post-procedure care. During the procedure, the patient’s condition is monitored, including assessment of voice and swallowing. For this reason, sedation was carefully titrated to maintain a RASS score between -1 and -2, which allows patients to remain responsive to verbal stimuli. This level of sedation provides several advantages: Reduces anxiety and discomfort, minimizes the risk of sudden or involuntary movements during needle manipulation, maintains effective communication throughout the procedure.

Following the procedure, all patients were transferred to the post-anesthesia care unit (PACU), where they remained under continuous monitoring for approximately 1 hour. During this period: patients were monitored by a critical care-trained nurse and instructed to report any discomfort or pain. Vital signs, blood pressure, oxygen saturation, heart rate, and continuous electrocardiogram must be recorded to detect possible systemic reactions, such as bradycardia, ST-segment changes, hypotension, or temporary vagus nerve irritation. Vital signs and clinical status were continuously assessed. Discharge was authorized only after full recovery from sedation and confirmation of adequate oral intake tolerance.

Discussion

Ultrasound-guided vagus nerve hydrodissection allows visualization of the nerve in the neck, typically near the common carotid artery and the internal jugular vein. Once identified, a solution is carefully injected to separate the nerve from neighboring structures without damaging it. This technique can alleviate symptoms resulting from entrapment or chronic irritation of the nerve.

Although promising, the evidence regarding vagus nerve hydrodissection remains limited and is largely based on case series and observational studies. Randomized clinical trials are lacking to validate its efficacy and standardize the techniques, doses, and solutions used (6).

Furthermore, as an interventional procedure, it requires a learning curve, proficiency in ultrasound, and in-depth anatomical knowledge to minimize risks such as vascular injury, hematomas, or excessive vagal dysfunction.

Vagus nerve hydrodissection has emerged as a promising intervention in the management of chronic pain with autonomic components, especially in patients with multisystemic dysfunction. This technique, guided by ultrasound and frequently performed with 5 % dextrose without local anesthetic, aims to release perineural adhesions and improve nerve conduction (6,7).

Vagus nerve dysfunction has been linked to multiple chronic pain conditions due to its key role in autonomic, inflammatory, and neuroimmunological modulation (8). Therefore, addressing it through hydrodissection represents a logical and physiologically grounded therapeutic strategy. In the case reported by Lam et al. (2024), a patient with chronic multisystemic pain experienced a marked improvement, similar to our patient, after three sessions of bilateral vagal hydrodissection, with resolution of autonomic symptoms and sustained pain reduction for nine months.

This approach contrasts with that of Eid et al. (2024), who present other therapeutic modalities such as transcutaneous vagus nerve stimulation (tVNS), which has demonstrated efficacy in chronic low back pain, but whose effects are more modest and involve an indirect mechanism. In particular, tVNS acts on the auricular branches of the nerve, and its efficacy depends on patient adherence and stimulation duration, unlike the one-time intervention of hydrodissection (9). Unlike the report presented by Lam et al., our approach was mixed; that is, in addition to hydrodissection —which in this report was bilateral— we performed high-voltage pulsed radiofrequency neuromodulation on both vagus nerves. This is based on the fact that the vagus nerve, in addition to carrying autonomic efferents, 75 % of the fibers are nociceptive afferents, so neuromodulation plays an important role in the management of chronic pain presumed to be modulated by the vagus nerve.

Peripheral nerve hydrodissection has shown promising results in other neuropathies; for example, in the treatment of carpal tunnel syndrome, the technique has proven safe and effective in increasing the diameter of the median nerve and reducing clinical symptoms, as evidenced by the systematic review by Sveva et al. (2024) (10). Similarly, in occipital neuralgia, Lam et al. (2024) documented a significant improvement in pain through hydrodissection of the greater occipital nerve (7).

In comparison, other studies have explored invasive interventions such as implantable vagal stimulation, with clinical benefits in refractory pain and cluster headaches, as presented in the study by Simmonds et al. (2023). However, these options involve greater risk and costs, highlighting the appeal of hydrodissection as a minimally invasive alternative (11). Adding pulsed radiofrequency may offer mechanisms complementary to hydrodissection alone.

Furthermore, recent research has emphasized the immunomodulatory role of the vagus nerve, particularly through the inflammation-autonomy axis. It has been demonstrated that its stimulation modulates the activity of cytokines such as TNF-α and IL-6, which are involved in the pathophysiology of chronic pain (12). Therefore, restoring its function through hydrodissection could not only alleviate pain but also modulate systemic inflammatory processes.

Despite encouraging findings, current evidence remains limited to observational studies and case reports. Controlled clinical trials are needed to compare hydrodissection with other therapeutic modalities and establish standardized protocols regarding solution volume, treatment frequency, and patient selection criteria.

This case should be interpreted as hypothesis-generating rather than confirmatory. The short-term improvement observed following the intervention targeting the bilateral vagus nerve may reflect a modulation of autonomic signaling, neuroimmunological pathways, perineural mechanobiology, or nonspecific contextual effects.

Since hydrodissection and pulsed radiofrequency were performed during the same session, it is not possible to determine the relative contribution of each component. Furthermore, the coexistence of fibromyalgia and ankylosing spondylitis complicates the mechanical attribution and limits generalizability.

Although interventions targeting the vagus nerve have been explored using non-invasive and implantable modalities, ultrasound-guided hydrodissection combined with pulsed radiofrequency may offer a minimally invasive alternative with a plausible mechanical basis. However, this remains unproven and requires validation in controlled studies.

Conclusion

In this case, bilateral ultrasound-guided vagus nerve hydrodissection, combined with pulsed radiofrequency, was associated with a clinically significant short-term improvement in refractory nocipathic pain. These findings should be interpreted with caution and considered as hypothesis-generating. Prospective studies are needed before this approach can be considered for wider clinical adoption.

references

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