Abstract

Objective

Pilonidal sinus disease (PSD) has been a recognized pathology for the past 188 years. We studied whether scientific interest in this common disease has grown or declined over time. Our investigation included analysis of the world literature between 1833 and 2018.

Patients & Methods

A PubMed search was conducted to identify all publications on pilonidal sinus disease, broken down by country, year of publication and number of patients included or described.

Results

The number of patients studied has been increasing, with date of more than 10,000 patients published per decade since 1970, and the total number of affected patients exceeding n=40,000 in 2010 and Turkey leads the research, contributing 39% of the Mediterranean patients and 18% of the patients globally, while Italy provides 26% of the Mediterranean patients and 12% of the global total. Flap studies have increased, whereas primary open treatment studies have decreased from 40% in 1940 to less than 10% at present. Twenty percent of the studies performed today report primary median approaches, and the number of randomized controlled trials has increased.

Conclusion

Surgeons in Turkey currently publish the lion´s share of the pilonidal sinus literature.

Introduction

Pilonidal sinus disease research began in 1847 with Dr. AW Anderson, who removed tufts of hair from a non-healing wound on the“back”of a young man. Shortly thereafter the wound healed, and the cure was published (1). Since then, there have been thousands of publications, ranging from case reports to studies containing several thousand patients. At the time, open wound treatment was considered the standard of care as this was a septic wound. This became a problem during World War II, when more than 70.000 soldiers were temporarily decommissioned due to open wound treatment for PSD, amassing 47.000 sick leave days in 1941 alone (2). Primary closure was attempted as early as 1933 (3), but wound complications were high in the pre-antibiotic era. Several subsequent publications focused on surgical methods, including H-like (4) and Star-like (5-7) incisions, partial closure, obliteration of dead space using metal wires (8-10) or cotton rolls (11-13), and even perceived advantages and disadvantages of surgical drains (14, 15). Roentgen irradiation, radioactive substances and obliterating substances were tried. When antibiotics finally became available to the surgical community (16) and asymmetric flap procedures increased, results improved-and research took off.

Contemporary work still mentions a number of therapeutic options, possibly either due to lack of comprehensive knowledge or to therapeutic negligence. In order to evaluate historical and current research efforts, we analyzed all publications addressing pilonidal sinus disease, from the first description up to the present literature, focusing on the number of patients treated and the number of articles published.

Material and Methods

We built a database with all of the literature found in a systematic search for the NCBI Medical Subject Heading (MeSH) term “pilonid*”, as well as “dermoid” AND “cyst” in MEDLINE, PubMed, PubMed Central, Scopus, Ovid, Embase, and the Cochrane Central Register of Controlled Trials (CENTRAL), as described previously by Stauffer (17) and Doll (18). In brief, all randomized, non-randomized, prospective, retrospective, and observational studies such as cohort, case-control, and cross-sectional studies, and case reports published between 1833 and 2017 were included. Figure 1 displays the results of the systematic search for evidence regarding recurrence and long-term follow-up data associated with common surgical procedures in PSD, based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA).

Specific details of data collection, data extraction and quality assessment, as well as grouping of therapeutic procedures and statistical analyses, can be found in the papers by Stauffer (17) and Doll (18).

Results

The average sample size was n= 73 patients (mean n= 33 ± 8 patients), with 60% of all studies published between 1833 and 2018 containing fewer than 50 patients (Figure 2). Thirty percent of the publications contained between 50 and 149 patients. Ultimately, 90% of all studies reported fewer than 150 patients on average. Sample size did not increase over time between 1940 and 2010, as illustrated by Figure 3. Here, the sample size over time was depicted from 1930 to 2010 (earlier publications are too scant to calculate a meaningful average). Please note that the values are given in mean ± SEM (standard error of the mean).

Interestingly, the sample size per publication did not increase over time, and has remained between n= 50 patients and n= 100 patients over the past 8 decades. In order to analyze whether interest in PSD has grown over time, we investigated the total study population over time. Adding up all publications over time in decades, another picture arose (Figure 4). As Figure 4 illustrates, the total number of PSD patients mentioned in pilonidal sinus publications has been increasing significantly since the 1940’s. Significant interest in the disease first arose during World War II due to the temporary decommissioning of more than 78.000 soldiers with PSD between 1941 and 1945 (19). Soldiers were absent for weeks and sometimes even months following surgery and primary open treatment. A more than fourfold increase could be seen during the first post-millennial decade.

While publications from North America (Canada and the USA) initially dominated between 1940 and 1950, interest seems to have decreased there, with cumulative numbers plateauing in the past 30 years (Figure 5). Conversely, interest from Northern Europe and the Mediterranean has shown a persistent increase over the past 6 decades. The Indo-Arab region started publishing study results from 2000 onwards. Asian patients are scant, and to our knowledge, there are still no studies from Africa. With the exception of isolated case reports, the disease seems to be practically non-existent among Africans.

In the Mediterranean region, Turkey and Italy are clearly the largest contributors to knowledge of PSD (Table 1). Italy contributed 25% of the Mediterranean patients, and 12% of the global total published between 1833 and 2018. Turkey heads the field, with 39% of Mediterranean and 18% of world PSD patients studied and published within this time frame.

Interest in primary open treatment seems to be decreasing (Figure 6). Flap surgeries are at the forefront, having been used in more than 30% of the studies. Twenty percent of the studies still appear to include primary midline closure, which is characterized by prohibitive long-term recurrence rates (17).

Recent literature reveals a 30:60 ratio of retrospective to prospective studies, with a clear decrease in the number of retrospective studies since the 1980’s. Despite being more laborious in terms of effort and resources, the perceived benefits and superiority of prospective studies are possible explanations (Figure 7).

Discussion

Our study shows that a large body of knowledge on pilonidal disease has accumulated in the past decades, and the numbers of both publications and patients recruited are still increasing.

Evidence for new surgical techniques has emerged over the past two decades, with flap techniques being studied much more often compared to primary open or midline technique. It is mindboggling that 20% of the patients studied were still treated with midline closure in 2010 despite prohibitively high recurrence rates. This was impressively shown by Stauffer et al., who analyzed the same patient data as we did (17). With a 32% recurrence rate at 10 years, midline closure is only surpassed by limited excision, with 34% recurrence at 10 years of follow-up (17). These techniques both exceed by far the currently accepted standard of care, delivering acceptable recurrence rates of 1% (good result) to 2% per year of follow up (20).

Most of the contemporary PSD research derives from the Mediterranean. Turkish surgeons have contributed a large body of evidence over the past 40 years, and the share is still rising. There are many potential reasons, including the large case load in the civilian and military populations (both overt and silent disease) (21-23), greater awareness of the disease among surgeons, and scientific interest.

There is increasing evidence that geographical location may contribute to recurrence rate and therapy efficacy (18), as well as social and familial factors (24-27). The large burden of patients has encouraged Turkish surgeons to publish research on the factors contributing to greater PSD incidence (23), such as cut hair removal (28-30) as well as regular showering (31, 32). New methods have been proposed (33-35), classifications defined, systematic reviews compiled (36) and rarities published (37-41). It is therefore understandable that-of all the general surgical articles in Turkey-15.4% cover pilonidal sinus disease and its treatment (42). More and more surgeons understand that the recurrence rate is a function of time, and while a rate of 2% per year of follow-up (i.e., 4% RR at 2 years) is acceptable, it can be lower (i.e., 5% at 3 years of follow-up) (20, 43, 44).

This goes hand in hand with an increased willingness to strive for more precise results through prospective randomized studies, which are shown to be increasing. Randomized controlled trials are generally conducted by large private and university-affiliated hospitals with specialized staff and research facilities. Nevertheless, small to midsize hospitals are the main location for pilonidal sinus surgeries, and the expertise of all surgeons involved in the treatment of pilonidal sinus disease is most welcome for inclusion in studies and publications.

We are aware of the limitations of our study, inherent in this type of epidemiological research. First, not all treated patients are included in published studies, and it would in fact be interesting to investigate this relation. Second, texts written in languages other than English, Spanish, French and German are lacking. Third, articles not indexed in PubMed, not published in larger journals, and not accessible via the Internet were not identifiable using our research algorithm. Fourth, there is a certain lag period between therapy, research, publication and the condensation of extended therapy results in a body of scientifically recognized knowledge. Analyses and recommendations for new therapies therefore often emerge following delays of several years.

It is therefore expected that analysis of additional publications in the coming years will shed more light on emerging and re-emerging techniques such as pit picking, endoscopic surgery and the use of lasers. More precise recurrence rates that incorporate longer follow-ups and new RCTs are to be expected.

The quality of studies has improved remarkably within the last decades, and is expected to increase further. Prospective randomized studies currently constitute 30% of the body of published articles.

Conclusion

In conclusion, both surgical interest and scientific activity are increasing in pilonidal sinus disease, and the Mediterranean region-especially Turkey-is contributing the lion ́s share to this body of evidence. As there is an increased interest in new treatment methods, new surgical approaches and respective evidence are eagerly awaited.