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From Direct Microscopy to Dermatoscopy

V. Crespo Erchiga & E. Gomez Moyano 

Dermatology Department. Hospital Regional Carlos Haya, Málaga, Spain

Dermatomycosis represent 15 to 20% of the skin diseases attended in the outpatient consultations in our Hospital. The predominant clinical forms are Dermatophytosis (ringworm): Tinea unguium and/or Onychomycosis, Tinea capitis and Tinea incognito, which shows an increasing incidence. We think that, although the clinical pattern can often suggest a clear diagnosis, this should be confirmed by performing a final laboratory diagnosis.

More than one hundred years ago, Raymond Sabouraud, a young French dermatologist, carried out a revolution in the knowledge, the etiology and, although less well known, in the treatment of superficial mycosis. Since then, and for many years, the dermatologists all over the world learned his strategies, got used to  managing microscopes, and preparing elemental culture media leading to the recognition of the main fungal species causing the dermatomycosis in patients  attending their hospitals or their private clinics.

The laboratory diagnosis of dermatomycosis performed by the dermatologists was carried out following three classic steps: The collection of the specimen, the direct microscopy performed in a portion of the sample, and the cultures in different media using the rest of the sample.

The aim of Direct microscopy, which was performed with the help of a simple reactive, usually KOH 20% solution with or without Parker Ink, or lactophenol, was the observation of fungal structures (hyphae, arthroconidia, blastoconidia…) that could be present in the specimen. Elsewhere, the cultures permitted the isolation and further identification of the fungi causing the disease, giving us a final and complete mycological diagnosis.

However, in recent years, dermatologists show a decreasing interest in the old laboratory techniques. In fact, it has been published that up to 75% of dermatologists in Spain manage their patients without any laboratory tests, 13% of the dermatologists in U.K. would treat their patients even with negative laboratory results and up to 60% of the Spanish dermatologists and 96% of general practitioners in Europe manage their patients according only to the clinical diagnosis, without any mycological confirmation .

The reasons for this preference for the empiric treatment of superficial mycosis, avoiding any laboratory help are probably multiple. To begin with, the clinical pattern is typical enough in most cases, and the introduction of broad spectrum antifungal drugs beyond the nystatine and griseofulvine has made the treatment easier. Also the fact that direct microscopy is easy to perform, but often difficult to interpret and is also time consuming. Also, the cultures are too complicated: there are too many culture media and too many different fungi, and their results demands waiting for weeks…. and there are serious doubts about the real usefulness of cultures in some important clinical forms, such as in onychomycosis. Many studies comparing the false negative results with culture and with direct microscopy in Tinea unguium showed more than 40% of false negative cultures.

At present, we can see that dermatologists perform less and less cultures or send the specimens to Microbiology Laboratories. On the other hand, they continue using direct microscopy, at least in some cases, as an easy technique to confirm the clinical diagnosis. I am sure that most of the diagnostic problems related with superficial mycosis can be solved just by means of this old technique, which can be carried out with just a common light microscope and one or two simple reagents….and some experience

Direct Microscopy allows a correct treatment schedule to be established without the help of culture results. In Pityriasis versicolor, the picture is pathognomonic. In Tinea incognito is always positive and in most cases the fungal structures are abundant and easy to find. Furthermore, DM is the diagnostic clue in cases of Tinea of vellus hairs, it allows easy recognition of the two main forms of parasitism (endóthrix and ectóthrix) in Tinea capitis, helping to choose the specific treatment and, finally, permits differentiating among Dermatophytes, yeasts and some moulds in onychomycosis.

Although the complementary practice of mycological cultures is always advisable, it is not indispensable in most of the cases from a practical point of view.

In recent years, an increasing number of papers have been published about the use of dermatoscopy in cutaneous mycosis. Although there is some mention on the diagnosis of pityriasis versicolor and Malassezia folliculitis (with the use of a modified dermatoscope with a Wood´s lamp), most of them are focused on Tinea capitis.

In scalp ringworm dermatoscopy findings which are considered to be of full or partial diagnosis value, have been described. These are the comma hairs (bent hairs), corkscrew hairs, Zig-zag , translucent/transparent and Morse Code hairs.

In a recent work on a group of cases of Tinea corporis with parasitism of vellus hairs (Tinea of vellus hairs), we identified translucent hairs in 83% of cases, follicular pustules in 67%, and corkscrew, dystrophic and Morse Code hairs in 20% of cases as well. We established the correlation between dermatoscopy and direct microscopy of Morse code hairs and its correspondence in clinical lesions.

Up to now, the role of direct microscopy remains of greater importance as a diagnostic tool in dermatomycosis, but can partly be replaced by the use of dermatoscopy, especially in mycosis affecting the hairs (Tinea capitis, Tinea barbae and Tinea of vellus hairs)