Collaboration with Johan Toonstra

Although I like to work alone, I have learned from working with Dr. Johan Toonstra that teamwork can be very fruitful. Johan has had his training as a dermatologist in Utrecht and has practiced at the Meander Medical Center (Amersfoort, Soest and Baarn). In addition, from 1983 to 2015, he was a parttime staff member of the dermatology department at the University Medical Center Utrecht. Our first contact was probably in 2004, when Johan co-authored an article I wrote entitled 'Annular skin disorders: under the spell of the ring' in Modern Medicine. At that time I was working on a series of articles for general practitioners in this journal for GPs with Vigfús Sigurdsson from Utrecht and Johan van der Stek from Rotterdam. Van der Stek took care of the pictures, because I myself had 0 (zero) images.

85.000 clinical pictures

I don't remember how Johan came to join us, but I assume that Vigfús has suggested it because of Johan's expertise in this area, because he also had a lot of images (he had about 85,000 at the time, it turned out) or both. Apparently we liked the collaboration, because in 2007 I asked him to co-write two articles in Bijblijven, Permanente Nascholing voor Huisartsen, a journal for general practitioners, of which I was the editor at the time. And in 2007 and 2008 he co-authored two articles in the Nederlands Tijdschrift for Dermatology and Venereology, one about skin disorders in diabetes mellitus and the other entitled 'Acne cosmetics: fact or myth?' The latter is especially important because there was not a single picture in it. So no one can accuse me of being a gold digger who was only after his unique collection of clinical images!

Dr. Johan Toonstra in 2020

Opposite characters

I had discovered other qualities in Johan that were useful to me, excuse me, useful to the collaboration, such as a large database of scientific articles and a solid and up-to-date knowledge of clinical and histopathological dermatology. That all suited me very well, because I hadn't practiced for years and couldn't keep up with the literature. This way Johan was able to remove the mistakes and imperfections that I made in our manuscripts (because he already took care of the images, I wrote most of the articles). And what was also important: he turned out to be a damn nice, quiet, modest and tolerant man, all of which are perfect and probably necessary qualities to be able to put up with such an easily inflammable character as I am for a while, to cooperate and to achieve results. And – spoiler alert – I can already report that the collaboration has gone very well indeed and has resulted in 15 joint books (12 titles) and 47 articles. Three books were published in 2020 and the most recent one this year, 2024 (see list below)!  


Our first book: Case reports in Dermatology (Casuïstiek in de dermatologie)

The cooperation first got off to a good start after we spoke in 2008 at a meeting in Nijmegen and Johan approached me afterwards. He told me that he had a lot of pictures and that he wanted 'to do something' with them. Did I perhaps have ideas? The years before I had developed a good relationship with Bohn Stafleu van Loghum (BSL) in Houten and I apparently suggested to Johan to contact BSL. Publisher Anita van Meyel from BSL showed us a little book entitled 'Case reports in surgery', and asked if we could make something similar in dermatology? We certainly could, and in a larger format, with much nicer and sharper images and not only one, but two volumes! We submitted the copy well ahead of the deadlines and our name was established at BSL. Later on we heard that we are the only authors who not only hand in the copy on time, but even before the agreed date.

Johan and I got the hang of it after the first Case Reports book and he  had a few more ideas. He wanted to make a new edition of the Dutch textbook  Dermatology and Venereology from 2000 (editors: W.A. van Vloten et al), in which we had both written a chapter. It would have to be new in the sense that we would write it together, completely new, without editors and chapter authors.

I wasn't much into that. It would be an awful lot of work and, moreover, there was already Dermatovenereology for primary care by Sillevis Smitt et al., which at that time already had its seventh edition (2003) and therefore was very well known with GPs. I doubted that we could compete with that standard textbook. But Johan had more irons in the fire. He has been giving lectures regularly to pedicures for a long time, because these professionals are regularly confronted with skin abnormalities on the feet.

Books for pedicures and podotherapists

There was no textbook/reference book about skin diseases for this group of paramedical professionals, so the decision to write one was made quickly and BSL was happy to participate. Voeten en huid ('Feet and skin') was published in 2009 and it was a great success in the foot care disciplines in the Netherlands. Afterwards,  we received a request from the professional group to also pay attention to the nails and we did so: Nail Disorders was published six months later. Writing was not very difficult for me and went quickly, because we had opted for many images and relatively little and simple text. Our intention was to provide a comprehensive overview of what pedicures may encounter in their practice. The trick was to arrange the contents in such a logical way that a pedicurist, who sees a skin or nail abnormality in a client, can easily find the image(s) that most closely resemble it and then read the corresponding text to assess whether this could indeed be the client's condition. Of course, a large number of good quality photographs are needed for this and Johan fortunately had an extensive arsenal of clear and razor-sharp images, which could also be zoomed in to make details visible.

We sometimes clashed over the choice of subjects. Johan tends to be exhaustive and I don't think it is useful to include extremely rare diseases such as leprosy or tuberculosis of the feet. Actually, this has been a point of discussion in various books, but we have always worked it out in good consultation and with giving (Johan a little more) and taking (me a little more)! Later we would write two new editions of these books, both published in 2016. In the same year, Feet and Cancer and Feet and Fungi were added, 4 years later Feet and Vessels and in 2023 Feet and Infections. We have renamed the second edition of Nail Disorders to Feet and Nails to conform to the other titles.

The books for pedicures are the most successful of all our (and my) publications. This is undoubtedly partly due to the large number of active pedicures (who often work part-time), but also because the publisher had an extensive network in this professional group through periodicals and conferences and was therefore able to reach them well. It is not least the merit of Johan, who over the years has given a very large number of lectures for pedicures, in which he, armed with brochures and order forms from the publisher, tirelessly and emphatically brought our books to the attention.

A new target group: skin therapists

In 2010 or 2011, Johan was contacted by Josètte Lorist, a leading skin therapist (huidtherapeute, a paramedical discipline largely confined to the Netherlands and Belgium). She wanted to make a textbook that fully meets the need for dermatological knowledge of skin therapy students and skin therapists. Johan asked me to participate in the project. Although it would be as much work as a book for GPs, I decided to at least have a talk with her and we arranged a meeting in Utrecht. The atmosphere was not optimal, to put it euphemistically. I didn't want skin therapy in the book, it had to contain only dermatology; mixing of the disciplines was out of the question for me. Josette undoubtedly interpreted this as that I looked down on her profession and the skin therapy practice and she was not easily persuaded.  That I insisted to include a statement in the book 'Dr. de Groot bears no responsibility for the skin therapeutic texts and indications in this book' was not really helpful for the already tense atmosphere. In the end, she agreed to limiting skin therapy to a general introductory chapter on this discipline and tables at the end of each chapter indicating which of the conditions could be considered for skin therapy and, if so, what treatment.

We have been working on that book for a long time, because Josètte and to a lesser extent Johan wanted to present dermatology in the fullest width, including extremely rare diseases. They also wanted to discuss sexually transmitted diseases (at the request of the skin therapy educators; and I thought: will people with STD ever visit the skin therapist for their infection?; I know the answer: NO). Nevertheless: here I had to give in (so not always 'take more than give'), all subjects had to be included in detail, including the dosage of medications (which skin therapists cannot prescribe). 

In 2012 Dermatology for skin therapists appeared, a sturdy book in A4 format of almost 650 pages and about 900 images, published by Boom Lemma in The Hague. Josètte had worked closely with the trainers of the skin therapy department at the universities of applied sciences in Utrecht and The Hague, where the book would be incorporated into the curriculum of the study. Educators, students and skin therapists were very enthusiastic and the book was soon termed the 'Bible of dermatology'. The second edition appeared in 2020. One of the first things Josètte had asked during the meeting at my house to discuss the second edition was whether 'that of not wanting to bear responsibility' still had to be included. I was now 7 years older and maybe a little bit milder and wiser and immediately answered 'no'. The atmosphere was excellent…….

Textbook of dermatology for general practitioners (in training) and medical students

After the first edition of Dermatology for skin therapists was published in 2012, the idea of a dermatology textbook, which I previously thought was too much work, naturally resurfaced. After all, we already had all the texts and they were broad and detailed enough for the target group of medical students and general practitioners (in training). Boom Lemma agreed to publish the book and we even had to shorten it a bit. Josètte was not amused, she thought that general practitioners should buy the book for skin therapists. But of course the skin therapy part got in the way there, so that had to be removed. In the end she agreed and Johan and I decided to give her a proportional share of the royalties of the new book for 5 years.

I was a bit afraid that our book Dermatology and venereology in practice (2012) would lose out to the long-standing Dermatovenereology for primary care, which was already in its eighth edition at the time. Johan thought that there was nevertheless room for another textbook, because Dermatovene-reology had no pictures, but a CD-ROM with pictures. That had been very modern at the time of its introduction, lots of beautiful pictures to look at on the computer, but now the lead that the book previously had now inhibited itself, because no one wanted to take the trouble to insert the CD-ROM anymore into the computer. Rumour had it that the authors of Dermatovenereology were so shocked when they saw our lavishly illustrated book that they went directly to the publisher of their book and demanded a new edition of their book with pictures. And thus, in 2014 a ninth edition indeed appeared with a button prominent on the cover shouting LARGE NUMBER OF CLINICAL IMAGES. 

There is now even a tenth edition. Incidentally, being honest: I think this textbook is better than ours in terms of didactics, probably because a professor of primary care medicine is one of the authors. Despite this, copies of our book were still sold every year. The book is now (mid 2023) completely sold out, but Boom Lemma (nowadays Boom Hoger Onderwijs) does not want to publish a new edition. I am sure they are quite right about that. Yet, it has been a worth while endeavour for us. 

Cancer and skin

In 2010, our book Cancer and Skin for general practitioners was published, which Johan and I had written at the request of Bohn Stafleu van Loghum. The publisher apparently did not have complete confidence that the book would be a commercial success, because they asked if I was willing to take on part of the costs. I had no objection to that and put 2000 euros on the table, but of course asked for a higher royalty percentage in return and that is what I received: 22.5%! Sales were going reasonably well, especially in the first years, and I more than got my investment out of it. We made a hit with this book in 2019, when a pharmaceutical company bought 300 copies to hand out to GPs (by the doctor's visitor, of course). Johan, who was not entitled to royalties, had been the driving force behind this deal, so I shared my royalties  with him.

Basal cell carcinoma, the most common form of skin cancer; characteristic are the shiny rim on the left, dull white-pink color in the center (pearlescent shine) and the ulcer, which has a crust (ulcus rodens)

Suspicious skin disorders

A formal second edition of the Cancer and Skin book has not been published, but we did write, at the request of Bohn Stafleu van Loghum, a derivative of it, Suspicious skin disorders. Case histories, differential diagnoses and background information, which appeared in 2020. In 2017, the NHG (Netherlands General practitioners Society) Standard  Suspicious Skin Disorders had been published. Our book is fully in line with the Standard and is designed to increase the knowledge that the general practitioner has gained from studying the Standard in an educational, visually attractive and exciting manner. The first part of the book contains 30 case histories, presenting the entire spectrum of conditions discussed in the standard. Each case starts with the image of a benign, premalignant or malignant skin lesion accompanied by some clinical data. One or more questions are asked about this. The answers to the questions are shown on the following pages, always accompanied by one or more other detailed images. The emphasis, both in the text and in the illustrations, is on how to distinguish between the various skin abnormalities, and in particular between benign and malignant lesions. In the second part of the book, all premalignant and malignant conditions mentioned in the NHG Standard are discussed in some detail.

Melanoma, the most dangerous form of skin cancer. The different shades of brown (light to very dark) and irregular shape are highly suspicious for this tumour, which was the cause of death for 750 people in the Netherlands in 2019. Melas is Greek for black

The tumor above is also a melanoma, but the pigment, characteristic of this form of skin cancer, is missing, except at the edge. This is called amelanotic melanoma. Due to the lack of brown color, this is usually recognized as a melanoma at a very late stage and the prognosis is therefore often worse than that of a pimented melanoma

Not only books and articles, also lectures

The collaboration between Johan and me has also resulted in a large number of publications, 47 in total, in Dutch journals. For the Nederlands Tijdschrift voor Dermatologie en Venereologie we wrote 31 articles, 26 of which in the section 'Test your knowledge', derived from our books Casuïstiek in de dermatologie.

Not only through our books, but also with lectures, we have tried to raise the dermatological knowledge of pedicures, podiatrists and other foot care providers to a higher level. By the way, Johan was considerably more active in this than I was, even during corona times. A number of times the two us us were the main act in conferences for these professionals, with 2 presentations each. After the publication of Feet and Skin (2009) and Nail Disorders (2010), for example, we held presentations on December 10, 2009, March 18, 2010, December 8, 2010, December 14, 2010 and May 17, 2011 in the Jaarbeurshallen in Utrecht, sometimes for as many as 400 foot care providers.

All conferences were organized by BSL, not coincidentally also the publisher of our books, which would sell like hot cakes during these events. On March 11, 2017, after the release of the second editions of the previous books and of the new book Feet and cancer and Feet and fungi (all 2016, it was a fruitful year), we gave lectures together again during the 'Seminar Dermatology for the Pedicure' in Nieuwegein, where we also had a signing session. After that, I lost my appetite for lecturing, but Johan is still very active.

Johan during a book signing session

At the moment (October 2022) Johan and I are writing the sixth part in the series Feet and ...... (Skin, Nails, Cancer, Fungal infections, Vessels) entitled Feet and infections for pedicures and podotherapists. If nothing special happens, that book will be ready at the end of this month. Perhaps after that, a long-standing, very fruitful and almost always pleasant cooperation will come to an end. But I wouldn't be surprised if Johan ever comes up with a new idea.......



We have indeed finished writing Feet and Infections, which was published early this year. And, as I suspected: Johan has suggested to write another book titled 'Hair and skin diseases for hairdressers'. We will soon start writing the copy together with our dermatologist colleague and friend Ids Boersma, who originally came up with the idea.



End of April 2024 the book for hairdressers was published by CocoBooks in Amsterdam. Ids was thrilled to be the first author. He deserves it: he came up with the idea, he has found a publisher who was also willing to give use handsome toyalties and, last but not least, he is a very nice guy!


Almost forgot: (almost) all clinical images on this website come from the collection of dr. Toonstra. Thanks for allowing me to use them, Johan!

List of books written by Johan and me

  • De Groot AC, Toonstra J. Casuïstiek in de dermatologie – deel I. Houten: Bohn Stafleu van Loghum, 2009 (ISBN 9789031361885)
  • Toonstra J, de Groot AC. Voeten en huid. Houten: Bohn Stafleu van Loghum, 2009 (ISBN 9789031352739)
  • De Groot AC, Toonstra J. Casuïstiek in de dermatologie – deel 2. Houten: Bohn Stafleu van Loghum, 2010 (ISBN 9789031384570)De Groot AC,
  • Toonstra J, de Groot AC. Nagelaandoeningen. Handboek voor pedicures, podotherapeuten en andere voetspecialisten. Houten: Bohn Stafleu van Loghum, 2010 (ISBN 9789031386185)
  • De Groot AC, Toonstra J. Kanker en Huid. Dermato-oncologie voor de huisarts. Houten: Bohn Stafleu van Loghum, 2010 (ISBN 9789031377503)
  • De Groot AC, Toonstra J, Lorist JM. Dermatologie voor huidtherapeuten. Den Haag: Boom Lemma uitgevers, 2012 (ISBN 9789059318199)
  • De Groot AC, Toonstra J. Dermatologie en venereologie in de praktijk. Den Haag: Boom Lemma uitgevers, 2012 (ISBN 978-90-5931-8977)
  • Toonstra J, de Groot AC. Voeten en huid, 2e edition. Houten: Bohn Stafleu van Loghum, 2016 (ISBN 9789036810463)
  • Toonstra J, de Groot AC. Voeten en nagels, 2editionHouten: Bohn Stafleu van Loghum, 2016 (ISBN 9789036813174)
  • Toonstra J, de Groot AC. Voeten en kanker. Houten: Bohn Stafleu van Loghum, 2016 (ISBN9789036810708)
  • Toonstra J, de Groot AC. Voeten en schimmels. Houten: Bohn Stafleu van Loghum, 2016 (ISBN 9789036811682)
  • Toonstra J, de Groot AC. Voeten en vaten. Houten: Bohn Stafleu van Loghum, 2020 (ISBN 9789036824156)
  • De Groot AC, Toonstra J, Lorist JM. Dermatologie voor huidtherapeuten, tweede druk. Amsterdam: Boom uitgevers, 2020 (ISBN 9789024428441)
  • De Groot AC, Toonstra J. Verdachte huidafwijkingen. Casuïstiek, differentiaaldiagnoses en achtergrondinformatie. Houten: Bohn Stafleu van Loghum, 2020 (ISBN 9789036824668)
  • Toonstra J, de Groot AC. Voeten en infecties. Houten: Bohn Stafleu van Loghum, 2023 (ISBN 9789036820168)
  • Boersma I, Toonstra J, de Groot A. Dermatologie voor haarprofessionals. Praktische gids over afwijkingen aan huid en haar. Amsterdam: CocoBooks, 2024 (ISBN 9789079142323)

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