It has been six years since the Swift microwave unit was launched in the United Kingdom, marketed to podiatrists in the treatment of warts and verrucae. I was lucky enough at the outset to undertake a number of projects assessing its effects on tissue and taking part in its first clinical study (1). Since that time, I have continued to publish work on the use of Swift in podiatry (2-5). In that time, development of new indications for the device has continued, particularly in the field of dermatology (6). The device is now marketed across much of the world. To date around 100 000 Swift treatments have been undertaken in the UK (200 000 globally) and the microwave technology has won numerous industry and healthcare innovation awards across the world. Most recently, receiving the prestigious CeeD Award for Innovation, a national community of businesses and academics which promotes engineering, education and development work, in February.
Plantar warts after first Swift treatment showing dried haematoma
As part of a company’s duty as a manufacturer of a medical device, they are obliged to regularly undertake post-marketing surveillance of the device to ensure its continued safety for use. Data from this exercise is not normally published but I was invited to examine this data along with my colleague, Dr Mike Ardern-Jones, from the University of Southampton with whom I undertook the original study work for the device (1, 2). This has been made available on MedRxiv (7) - an online preprint server which holds manuscripts, prior to peer review and publication.
So, what was the study? The company issued at 79-item survey of all its UK based users. This was undertaken via an online survey tool, and the data was compiled and analysed. In total 126 clinics using Swift responded to the request and took part in the survey. The data collected covered the treatment of 6998 adults with warts. Of these 5733 were described as plantar while the remainder as non-plantar. The median efficacy rate (on a per patient basis) was 79.2% for plantar warts and 82.3% for non-plantar lesions. When the data was divided between adults and older adults (over 65’s) the resolution rate was similar 73.2% for plantar warts and 80.0% for non-plantar lesions. The median number of treatments employed by clinics was 4, with a median review of 3 months after the last treatment. Interestingly, when clinics were asked if they treat all or some of the lesions at each session, around two thirds treated all lesions present whilst a third treated just the primary lesion(s). When examined further, resolution rates showed no difference between those who only treated the primary lesion versus those who treated all lesions present, suggesting a widespread immune response.
Plantar wart two months after SWIFT treatment was completed
Resolution rates in patients with diabetes or immune affecting disorders was also collected. The data suggested that patients with diabetes showed a similar resolution rate to those without the condition (79.6% clearance). However, as expected, patients with known immunosuppressive conditions showed a clearance of around 61%. A small number of adverse events were recorded by 13 clinics in just under 7000 treatments. These included cases of poor healing, ulceration or blistering at the treatment site. One clinician identified two cases of lymphangitis which upon investigation were deemed non-device related.
This work confirms the original clearance rate as reported in the first published study but represents data from a wider range of patients (nearly 7000) and includes non-plantar lesions which showed increased clearance rates possibly because they occur on thinner skin, so microwave penetration is slightly better, and its effect is greater. The safety profile of the device has been confirmed with a small number of adverse effects reported, most such as ulceration, blistering, pain and haematoma which were all previously known.
As the technology is being used for new pathologies and in new territories, further studies are underway to evaluate its effectiveness for HPV related lesions and other conditions.
References
1. Bristow IR, Lim W, Lee A, Holbrook D, Savelyeva N, Thomson P, et al. Microwave therapy for cutaneous human papilloma virus infection. Eur J Dermatol. 2017;27(5):511-8.
2. Ardern-Jones M, Lee A, Chean LW, Holbrook D, Savelyeva N, Thomson P, et al. Induction of antihuman papillomavirus immunity by microwave treatment of skin. Br J Dermatol. 2016;175(Supp 1):151.
3. Bristow IR, Webb CJ. Successful Treatment of Hard Corns in Two Patients Using Microwave Energy. Case reports in dermatology. 2020;12(3):213-8.
4. Bristow IR, Ardern-Jones M. Treating verrucae effectively with microwave energy – are we getting warmer? Podiatry Now. 2017;20(6):21-3.
5. Bristow IR, Webb C, Ardern-Jones M. The Successful Use of a Novel Microwave Device in the Treatment of a Plantar Wart. Case reports in dermatology. 2017;9:102-7.
6. Jackson DN, Hogarth FJ, Sutherland D, Holmes EM, Donnan PT, Proby CM. A feasibility study of microwave therapy for precancerous actinic keratoses. Br J Dermatol. 2020;183(2):222-30.
7. Bristow I, Joshi SC, Williamson J, Ardern-Jones M. Post marketing surveillance for Microwave Treatment of Plantar and Common Warts in Adults. Medrxiv. 2022. doi.org/10.1101/2022.02.08.22270290