Search outcomes
For the VNS and SNS searches, we initially identified 69 and 27 records, respectively, from the PubMed database, which were then imported into the EPPI Reviewer software.42 Upon screening, all records were successfully retrieved and assessed for eligibility. Among the 89 records excluded, 64 were related to VNS, and 25 were related to SNS. The exclusions comprised 51 reviews (39 VNS and 12 SNS), 27 animal studies (19 VNS and 8 SNS), 7 records without an assessment of IBD symptoms (2 VNS and 5 SNS), 1 case study (VNS), 1 abstract (VNS), 1 study protocol (VNS), and 1 record unrelated to VNS therapy.
Subsequently, we included 7 records in the analysis: 5 for VNS and 2 for SNS. A visual representation of the record selection process is depicted in Figure 1 using the PRISMA flow diagram. The results of the VNS and SNS studies are summarized in Tables 2 and 3,43–49 respectively. These tables present the IBD symptom outcomes as the mean ± standard deviation of the difference between post-therapy data and pre-therapy data.
Table 2Summary of three clinical studies evaluating the effects of VNS therapy on CD and UC
NCT number, duration | N per arm | Daily therapy dose | CDAI, pCDAI, pUCDAI | CDEIS | GI-related VAS | CRP (mg/l) | FC (µg/g) | LF/HF | Ref. |
---|
NCT01569503, 6 months | 5 CD | 2.2 h (24 h * 9%) | Δ −166 ± 58, p < 0.01 | Δ −6.8 ± 1.5, p < 0.001 | Δ −2.1 ± 1.4, p < 0.05 | Δ −3.6 ± 5.7, p > 0.05 | Δ −1,070 ± 1,301, p > 0.05 | Δ −2.4 ± 2.3, p > 0.05 | 43,44 |
NCT01569503, 12 months | 7 CD | 2.2 h (24 h 9%) | Δ −156 ± 62, p < 0.001 | Δ −4.2 ± 4.1, p < 0.05 | Δ −1.9 ± 1.9, p < 0.05 | Δ −7.9 ± 9.3, p > 0.05 | Δ −1,168 ± 912, p > 0.05 | Δ −1.7 ± 2, p > 0.05 | 45 |
NCT02311660, 4 months | 12 CD | 20 min (5 min * 4x) | Δ −115 ± 24, p < 0.001 | ND | ND | Δ −0.9 ± 0.9, p > 0.05 | Δ −3,209 ± 937, p < 0.01 | ND | 46 |
NCT03863704, 3.5 months | 10 CD | 10 min (5 min * 2x) | Δ −15 ± 17, p < 0.05 | ND | ND | ND | Δ −357 ± 800, p > 0.05 | ND | 47 |
NCT03863704, 3.5 months | 12 UC | 10 min (5 min * 2x) | Δ −8 ± 15, p > 0.05 | ND | ND | ND | Δ −833 ± 250, p < 0.05 | ND | 47 |
Table 3Summary of two clinical studies evaluating the effects of SNS and sham therapies
NCT number, duration | N per arm | Daily therapy dose | UCDAI | Mayo score | TNF-α (pg/ml) | CRP (mg/l) | FC (µg/g) | LF/HF | Ref. |
---|
NCT02748590, 4 months | 8 UC + SNS | 24 h | Δ −1.5 ± 2.8, p > 0.05 | ND | ND | ND | Δ −234 ± ND | ND | 48 |
N/A, 2 weeks | 15 UC + SNS | 6 min (60 min *10%) | ND | Δ −2.1 ± 1.8, p < 0.01 | Δ −9.5 ± 8.9, p < 0.001 | Δ −6.6 ± 9.9, p < 0.05 | ND | Δ −0.68 ± 1.78, p > 0.05 | 49 |
N/A, 2 weeks | 11 UC + sham | 6 min (60 min *10%) | ND | Δ −0.6 ± 1.3, p > 0.05 | Δ −5.4 ± 14.1, p > 0.05 | Δ −1.0 ± 6.7, p > 0.05 | ND | Δ 0.96 ± 1.13, p < 0.05 | 49 |
VNS studies
We identified three VNS studies, including two open-label single-arm iVNS studies (with VNS electrodes implanted on the cervical vagus) and one RCT taVNS study (with transcutaneous auricular VNS electrodes).
In two iVNS studies, NCT01569503 and NCT02311660,43–46 bipolar electrical stimulation was delivered via the helical cuff electrode (Model 302 or 304, Cyberonics) implanted on the left cervical vagus nerve and tunneled to an IPG (Model 102 or 103, Cyberonics), which was placed in the subcutaneous pocket on the left chest wall. The first iVNS study (NCT01569503) was performed in Grenoble, France, where 7 adult patients with moderate CD (220 ≤ CDAI ≤ 450) diagnosed for at least 3 months before enrollment and naive of biologic treatment were subjected to iVNS with the following parameters: frequency of 10 Hz, current amplitude of 0.5–1.25 mA, pulse width of 500 µs, duty cycle of 9% (0.5 min every 5.5 min), delivered continuously for 12 months.43–45 The second iVNS study (NCT02311660) was performed at four European locations (Zagreb, Croatia; Milano, Italy; Amsterdam, Netherlands; and Stockholm, Sweden), where adult patients with moderate CD (220 ≤ CDAI ≤ 450, SES-CD ≥ 2 in at least one segment, and FC ≥ 200 ug/g) diagnosed for at least 4 months before enrollment and refractory or intolerant to at least one biologic treatment (infliximab, adalimumab, or vedolizumab) were subjected to iVNS with the following parameters: frequency of 10 Hz, current amplitude of 0.25–2.0 mA, pulse width of 250 µs, duty cycle of 100%, delivered for 5 minutes four times per day for 4 months.46
In the taVNS study NCT03863704,47 active bipolar electrical stimulation was delivered via the hand-held skin probe with two electrodes (Blue Moon Health) placed on the cymba concha area inside the left ear, while sham electrical stimulation was delivered in the middle of the left calf, with the cross-over design, where patients served as their controls. The study was performed in New York, USA, where pediatric and young adult patients (10–21 years) with mild and moderate CD and UC (FC ≥ 200 ug/g) diagnosed for at least 3 months prior to enrollment and irrespective of biologic treatment (only those on infliximab were excluded) were subjected to taVNS with the following parameters: frequency of 20 Hz, current amplitude just below the pain threshold, pulse width of 300 µs, duty cycle of 100%, delivered for 5 minutes two times per day for 3.5 months.47
The results of three VNS studies are summarized in Table 2.
The clinical studies examined the long-term effects of iVNS and taVNS on IBD symptoms, with a follow-up period of up to 12 months for iVNS and 3.5 months for taVNS.
In all iVNS and taVNS studies, a significant reduction in IBD disease activity was observed in CD patients. This reduction was assessed using the CDAI and GI-related VAS in adults and the pCDAI in adolescents. However, this reduction was not observed in adolescent patients with UC who were treated with taVNS, as assessed by the pUCDAI.
One of the iVNS studies (NCT01569503) also demonstrated a significant long-term improvement, both at 6 and 12 months, in the severity of intestinal lesions, assessed endoscopically as the CDEIS, as well as in intestinal pain, assessed using the GI-related VAS.
Two iVNS studies (NCT01569503, NCT02311660) additionally assessed blood biomarkers, including CRP, and fecal biomarkers, including FC, for intestinal mucosal inflammation. In both iVNS studies, CRP was not significantly reduced in CD patients. However, FC was significantly reduced in only one of the two studies (NCT02311660).
Regarding the taVNS study, FC was assessed, but the results were inconclusive. FC was significantly reduced in UC patients but not in CD patients.
One of two iVNS studies (NCT01569503) evaluated a possible mechanism of action for the VNS therapy, the recovery of the autonomic balance (assessed as the LF/HF ratio of the power spectrum of the HRV derived from the electrocardiogram) and, while there was a trend toward a decreased sympathetic dominance at both 6 and 12 months, it was not statistically significant.
The iVNS therapy is associated with the risk of surgical and post-surgical complications. Among 16 implanted subjects in the NCT02311660 study, one experienced transient postoperative skin infection requiring device explantation. No complications were reported in the NCT01569503 study. In both iVNS studies, the VNS-related adverse effects included only discomfort due to voice hoarseness, a typical iVNS side effect. In the taVNS study (NCT03863704), one subject developed a transient skin redness and a minor break in the skin because of excessive pressure applied to the ear with the taVNS probe during the first week of stimulation, which was resolved by further educating the subject on the taVNS technique.
SNS studies
We identified two studies related to SNS: one open-label single-arm study involving implantable SNS electrodes (iSNS) and one RCT focusing on percutaneous SNS electrodes (pSNS).
In the iSNS study, registered as NCT02748590,48 bipolar electrical stimulation was administered through a 4-electrode SNS lead (Model 3889, Medtronic) implanted within the S3 foramen. The lead was then tunneled to connect with an IPG, specifically the InterStim II (Model 3058, Medtronic), placed in a subcutaneous pocket on the left chest wall. This study was conducted in Nantes, France. It involved eight adult patients diagnosed with moderate ulcerative UC who exhibited a UCDAI ranging from 6 to 9 and an endoscopic UCDAI score of at least 2. These patients had been diagnosed with UC for at least 2 years before enrollment and were resistant to immunosuppressive or biologic anti-TNF treatments. During the iSNS intervention, the following stimulation parameters were employed: a frequency of 14 Hz, a current amplitude of 1.1 V, a pulse width of 210 µs, a duty cycle of 100%, and continuous stimulation for a duration of 4 months.48
In the pSNS study,49 bipolar electrical stimulation was delivered via four stainless steel acupuncture needles (diameter 0.45 mm, length 100–125 mm) inserted bilaterally inside the S3 and S4 foramens and attached to an external stimulator (Transcutaneous Electrical Applicator, Model SNM-FDC01, MedKinetic Medical Device Co. Ltd, Ningbo, China), while the sham electrical stimulation was delivered using the same needles placed 20 mm downward and 8–10 cm lateral from these sacral foramina. The study was performed in Nanjing, China, where 26 adult patients with mild and moderate UC (3 ≤ Mayo score ≤ 10) diagnosed for at least 3 months prior to enrollment were subjected to pSNS with the following parameters: frequency of 5 Hz, current amplitude of 2–10 mA, pulse width of 500 µs, duty cycle of 10% (10 sec every 100 sec), delivered for 1 hour per day for 2 weeks.49
The results of two SNS studies are summarized in Table 3.
The clinical studies evaluated the medium-term effect of iSNS and pSNS on IBD symptoms with a follow-up period of 4 months for iSNS and 2 weeks for pSNS. Only the UC patients were evaluated in both studies: in the iSNS study, the UC disease activity assessed as the UCDAI was insignificantly reduced, while in the pSNS study, it was assessed as the Mayo score and was significantly reduced in the SNS arm but not in the sham arm. The pSNS study also assessed the blood biomarkers of intestinal mucosal inflammation (TNF-α and CRP), with both biomarkers significantly reduced in the SNS arm but not in the sham arm. In contrast, the iSNS study assessed the fecal biomarker FC, and while the FC level was reduced post-SNS, no statistical significance calculation was provided for that effect.
The pSNS study also evaluated a possible mechanism of action for the SNS therapy, the recovery of the autonomic balance (assessed as the LF/HF ratio). While there was a statistically insignificant trend toward a decreased sympathetic dominance in the SNS arm, the sympathetic dominance significantly worsened in the sham arm.
The iSNS therapy is associated with the risk of surgical and post-surgical complications. Among 8 implanted subjects in the NCT02748590 study, one lead disconnection occurred during the test phase, while the implanted lead was percutaneously connected to the external stimulator. There were no SNS-related adverse effects in both the iSNS and pSNS studies.