Survey on mycological diagnostics in dermatology - results

During the past years, there has been a change in mycological diagnostics: the development of PCR-examinations is a relevant and efficient method to determine fungal pathogens. But do we really need PCR-testing in mycology? Which impact and relevance has PCR-testing in our daily routine? And which are the preferred diagnostical methods? To answer these questions, we launched a survey among Swiss dermatologists in October 2022. We appreciate every response, and we present the results below.

A total of 1064 dermatologists and residents in dermatology (readers of Dermatologica Helvetica / SGDV newsletter) received a link to a voluntary online survey on the use of mycological diagnostical tools (direct microscopy, culture, PCR) in their daily routine and numbers of the respective analysis in 2021. 104 persons completed the survey (82 chose the German version, 22 the French one). Most of the participants worked in a practice (89%, mainly as practice owners), and the rest worked in hospitals (11%).

An overwhelming majority (96%) stated that they take material for direct microscopy (fig.1). However, only 83% of all respondents (and only 54% of the persons who chose the French version) evaluated it themselves. The average amount of examined direct examinations per year and per person was 157.2, with a large spread (from 5 to 2500).

Samples for mycological cultures are obtained by 92% of all surveyed (18 persons skipped this question). Only seven persons stated they did not initiate mycological cultures at all, but six used PCR-analysis instead. Among those who took samples for mycological cultures, 44% evaluated the cultures themselves. A difference between the German and French answers was observed (German-speaking: 52%, French-speaking:18%). About 106.3 mycological cultures were collected per person in 2021 (ranging from 0 to 1000).

A total of 65% of persons have already used PCR-analysis, mostly in external laboratories but also within their own (18 participants skipped this question). Those who have already used PCR-analysis took 60.5 samples in 2021 (range from 0 to 400). Those who have not used PCR-analysis yet (30 persons in total) were then asked if they would be interested in this diagnostic tool in the future. 50% answered «yes», 33% answered «possibly,» and only 17% said they were not interested

The survey has a few limitations since not every Swiss dermatologist answered it. Due to the small number, we did not further evaluate the answers depending on the respective professional position (chief medical officer / resident / practice owner etc.).

However, the 104 responses we received give a good overview of the current opinion of Swiss dermatologists concerning mycological diagnostical tools.

Direct examinations (preparation with potassium hydroxide and immediate microscopic examination) are a cheap possibility to analyze samples (scales, nails, hair) during consultation hours. The result is available after a few minutes- however, the sensitivity strongly depends on the examiner. Most Swiss dermatologists use this fast and easy method, but one resident critically remarked that this technique is not taught enough and therefore takes too much time. Offering more mycology courses should be considered.

For the determination of the fungus species – which has a huge impact on treatment and epidemiological considerations – further examination is needed. Our survey showed that 99% of all respondents performed either mycological cultures or PCR testing or both.

Mycological cultures used to be the gold standard before PCR testing was established. In our daily routine, we sometimes have difficulties with the interpretation due to mold growth and delivery problems of the culture plates. Additionally, it takes up to four weeks until the result is fixed. And yet it has the big advantage that hardly any material or infrastructure is needed. One participant in the survey stated she or he would love to stick to this cost-effective tool in the future.

PCR analysis certainly has some advantages when compared with mycological cultures. Results are obtained within hours; it is more sensitive (and especially helpful when cultures cannot be interpreted due to mold) and can also be performed under treatment. In contrast to direct microscopy and fungal culture it is not yet part of the list of analyses for dermatology, so PCR for mycological purposes in dermatology is not covered by public health insurance in Switzerland. PCR analysis is slightly more expensive than fungal cultures – but when it comes to calculating the overall costs, one should also consider that with this fast method, an adequate antifungal therapy can be started immediately. Costs of initial «wrong» treatments can be reduced, and the further spreading of diseases – which also leads to further expenses – can be prevented.

With this survey we showed that there is a big interest in PCR analysis among Swiss dermatologists. A majority (65%) of all respondents to this survey already used this technique, and most of the other respondents stated they were interested (fig. 2).

We received several valuable comments on this topic, and we would like to address some of these comments in more detail:

Self-performing PCR in mycology, including quality assurance requirements, is probably too technical and financially costly for dermatologists in private practice?

Currently, it is indeed rather costly since PCR-analysis is not yet reimbursed by health insurance. A team of the SGDV/SSDV just submitted a cost assumption application to the BAG (Bundesamt für Gesundheit). Remuneration of culture should not be replaced by PCR. It should be possible to use either method for pathogen differentiation.

Spoken from a practical point of view, it is possible to perform PCR-analysis within a #SONDERZEICHEN6#regular” dermatological practice. However, the prerequisites are three separate premises, some laboratory equipment, and sufficient manpower (one MPA needs empirically 3 hours to analyze 14 samples, plus an additional 30min of evaluation by a doctor). Given these circumstances, implementation of PCR-analysis probably only makes sense in larger practices (cf. [1]).

Recommendations are needed when an expensive PCR makes sense and when it does not.

The recently published German guideline on onychomycosis for example recommends the use of PCR in combination with microscopic preparation and fungal culture as a complementary detection method because of its sensitivity. PCR is also recommended to control successful therapy of onychomycosis [2]. The German guideline on tinea capitis recommends the determination of the pathogenic fungus either by mycological culture or by PCR [3]. Both guidelines see a benefit of PCR examination when patients are already under treatment. However, a need for further research on the importance of PCR in follow-up was also stated in the guideline on tinea capitis.

The PCR examination might give «false positive» results, i.e. molds are indicated which are not relevant in the specific case.

PCR examination is a very sensitive and specific method. Some commercial testing systems offer a wide range of determinable fungi (which might not always be of relevance, especially molds) and contaminations might also occur. We believe it is essential to evaluate PCR-results critically and take the clinical picture into account before initiating an antifungal therapy.

There seems to be a considerable interest in all forms of mycological analysis (direct microscopy, fungal cultures, and PCR testing) among Swiss dermatologists. Regular training and Swiss guidelines / algorithms concerning diagnostic strategies might be helpful. If PCR-testing was reimbursed by health insurance in the future, we would have another helpful and specific diagnostic tool for our daily routine.

Dr. med. Katharina Belge, Dr. med. Heinrich Grob

Praxis Reinacherhof, Reinach (BL)