Onychomycosis: Recommendations for Diagnosis, Assessment of Treatment Efficacy, and Specialist Referral. The CONSONANCE Consensus Project

Onychomycosis is a common fungal infection of the nails caused by dermatophytes, non-dermatophyte molds, and/or yeasts. It is the most common nail disorder in adults and accounts for approximately 50% of all nail-related diseases. Onychomycosis is divided into five subtypes based on the pattern of fungal invasion, of which distal lateral subungual onychomycosis (DLSO) is the most common presentation (58–85% of all presentations) [1, 2]. Onychomycosis risk factors include advanced age, diabetes, and immunosuppression, among others [3], and the infection has a wide variability in prevalence (from < 1% to 28%), depending on the country, patient age, and responsible fungus.

Clinical evaluation of onychomycosis may be challenging because other conditions, such as psoriasis, lichen planus, or traumatic onycholysis, can be misdiagnosed as onychomycosis. Onychomycosis may be caused by a variety of fungal agents which respond differently to antifungal treatments; consequently, an accurate diagnosis is essential before commencing therapy [4]. Routine diagnostic techniques include direct microscopy with potassium hydroxide (KOH), fungal culture, histopathology, and PCR testing [5]. Dermoscopy (onychoscopy) can also be used to identify DLSO [6]. However, these techniques may not be available to general practitioners, who are usually the healthcare providers who provide the clinical diagnosis. According to the National Ambulatory Medical Care Survey (2007–2016), dermatophytosis is predominantly diagnosed by general practitioners (40.3%), followed by dermatologists (26.4%), and pediatricians (26.2%) [7].

The most common therapies for onychomycosis include oral and topical antifungals, often employed concomitantly with physical treatments (clipping, debridement, etc.) [8]. Onychomycosis therapy must be individualized, taking into account the extent and severity of nail abnormalities, the causal agent, and the characteristics and preferences of the individual patient, to avoid side effects and potential polypharmacy issues.

The aim of the CONSONANCE (CONSensus on ONychomycosis Assessment in Non-specialized Clinical Environments) project is to provide recommendations on the minimum clinical criteria needed for DLSO diagnosis and the assessment of treatment efficacy by healthcare professionals not specialized in nail diseases and other non-expert healthcare professionals in their daily clinical practice, as well as to issue recommendations for patient referral.

A questionnaire was distributed among members of the European Nail Society (ENS) to define recommendations for onychomycosis diagnosis, treatment efficacy assessment, and criteria for patient referral in non-specialized environments. No criteria for participation other than ENS membership were established.

The CONSONANCE project occurred in five successive phases: scientific committee creation, survey questionnaire development, survey administration, data collection, and data analysis.

The ENS established a scientific committee consisting of six experts in nail diseases from five different countries. This scientific committee developed a 26-item questionnaire (Electronic Supplementary Material 1) containing three main sections: participant profile, current clinical practice for DLSO diagnosis and treatment, and essential recommendations for non-experts to establish the diagnosis of DLSO, as well as definitions of treatment efficacy and reasons for referral. The full ENS membership was invited to participate, and the questionnaire was issued online from 20 October 2020 through to 9 December 2020, via an online platform that ensured data anonymity and confidentiality.

Ethics Committee approval was not applicable in this study because it is an opinion-based survey among healthcare professionals. There was no need to collect any type of patient data. Hence, the approval of an Ethics Committee was not required.

For diagnosis of DLSO, all participants always evaluated the clinical aspects of the nail. 95% always or often asked for relevant medical history, and 91% always or often employed onychoscopy. In agreement with current recommendations [1], microscopic examination of a nail sample prepared with KOH and fungal culture were always or often performed by 81% of the respondents in both cases. At follow-up, clinical aspects of the nail were always or often evaluated by 100% of the participants, and dermoscopy was always or often performed by 86% of the participants (data not shown).

The treatments most often used for onychomycosis include oral antifungal treatment (47%), topical antifungal treatments (40%), and nail debridement (29%). For first-line therapy, topical antifungals were used in 88% of the cases when < 50% of the nail was affected. However, when > 50% of the nail, or the matrix was affected, combined oral and topical, or oral antifungals alone were prescribed by > 70% of the respondents. Nail avulsion and nail debridement were also employed in cases of more severe DLSO.

Regardless of disease severity, the follow-up interval of patients with DLSO was reported as every 3 months. The main criterion to establish cure for nail experts was “complete cure” (i.e., both mycologic cure and clinical cure) (used by 54% of the respondents); however, 34% of the survey participants indicated that they only take into consideration the “clinical cure” (completely normal nail clinically). The survey participants reported taking the decision to stop treatment based on the following factors: mycologic cure (negative result upon KOH-stained microscopic examination and culture) (22% of the participants), clinical cure (29%), or both (29%) (data not shown).

The CONSONANCE project provides data from nail experts based their current clinical practice for the diagnosis, treatment, and follow-up of DLSO. Moreover, the project aims to guide DLSO management in non-expert environments (dermatologists not specialized in nail diseases, general practitioners, and pharmacists). The participants and the Scientific Committee agreed with the minimum clinical criteria for DLSO diagnosis, treatment efficacy assessment, and patient referral. The recommendations appear to corroborate existing knowledge [1], although they focus on healthcare professionals that do not usually have the specific knowledge and access to diagnostic tests and equipment to properly diagnose and manage onychomycosis.

A thorough physical examination is essential for DLSO diagnosis, especially in non-expert environments where access to specialized equipment and diagnostic tests is limited or non-existent. According to the British Association of Dermatologists (BAD) guidelines, the clinical presentation of DLSO includes nail discoloration, thickening, onycholysis, and subungual hyperkeratosis [1]. All participants in the present survey agreed with the BAD recommendation that is important to evaluate the clinical aspects of the nail for diagnosis.

A proper anamnesis, including comorbidities, habits, and patient occupation, is also important when there is a suspicion of DLSO. An increased prevalence of onychomycosis in patient populations with impaired immunity has been reported. Overall, 79% of survey participants considered it totally necessary to inquire about concurrent immunosuppressive diseases, such as HIV infection and diabetes mellitus. The prevalence of dermatophyte toenail onychomycosis has been reported to be around 3-fold more common among HIV-positive individuals and diabetic patients than in the unaffected population [9]. Furthermore, 68% of the survey participants considered assessing psoriasis as a predisposing factor for DLSO diagnosis. In addition, in a survey conducted among members of the Canadian Society of Dermatology, respondents considered that comorbidities, such as diabetes and peripheral vascular disease, should be assessed [10]. Diabetes and peripheral vascular disease were predisposing factors thought to be considered by 76% and 55% of the participants in the present survey, respectively. Other fungal infections, such as tinea pedis plantaris and tinea pedis interdigitalis, are described as risk factors for onychomycosis [5], and 95% of participants in the present survey considered it to be totally necessary to evaluate concurrent tinea pedis when suspecting DLSO. In addition to biological predisposing factors, also environmental risk factors for onychomycosis have been previously described. Although the underlying mechanisms for onychomycosis transmission have not been elucidated, household contact has been identified as a major risk of onychomycosis transmission. Evidence of transmission in almost half of households with at least one affected subject has been reported, highlighting the role of households in the spread of onychomycosis [11].

Together with clinical evaluation and assessment of predisposing factors, it is important to consider other conditions or nail infections that are included in the clinical differential diagnosis of onychomycosis. The foremost challenge to healthcare providers is to differentiate DLSO from nail unit psoriasis, traumatic onycholysis, and nail unit lichen planus. The consideration of nail unit psoriasis is based on a potential clinical history of psoriasis, skin signs, arthritis, finger nail involvement, presence of nail signs (such as pits), and salmon patches. For the consideration of nail unit lichen planus, the clinical history needs to be taken into consideration, as well as skin signs, involvement of mucous membranes and of the hair, and presence of nail signs (such as thinning, longitudinal fissuring, and dorsal pterygium). Traumatic onycholysis can be confirmed by a complete podiatric examination. In addition, there are also some worrisome signs which indicate that patients need a prompt referral to a nail specialist, including when the disease spreads to other toe-/fingernails and the presence of paronychia with serum or pus discharge (Fig. 3).

DLSO often has a similar clinical presentation if caused by dermatophytes, non-dermatophytes, or yeasts [1], but these organisms may respond differently to antifungal agents [4]. Therefore, it is important to identify the causative organism before starting treatment. In our study, mycologic confirmation was a common practice among survey participants, with the percentage reporting mycologic confirmation (81%) higher than previously reported by Koshnick et al. among dermatologists (63.6%) [12]. According to Koshnick et al., in non-specialist environments, up to 46.6% of family practitioners and 21.6% of podiatrists do not obtain a confirmatory diagnostic test before starting treatment of toenail onychomycosis [12]. This lower percentage could possibly be explained by limited access to laboratories able to process fungal cultures. Subsequently, therapy can sometimes be initiated based on clinical presentation alone. A recent study showed that performing confirmatory testing before starting treatment with both topical and oral antifungals is cost-effective [13], and this recommendation is even stronger when any oral antifungal treatment is considered [14]. Identification and treatment of onychomycosis are essential because the disease has a great impact on patients’ lives, involving psychological and physical effects, and also a great socioeconomic impact (occupational life) [15‐17]. The importance of confirming the diagnosis of onychomycosis before prescribing an oral antifungal is supported by the first recommendation of the American Academy of Dermatology’s (AAD) contribution to the Choosing-Wisely campaign [18].

Even if clinical trials for onychomycosis use mycologic cure (negative mycologic culture and KOH) and clinical cure as primary endpoints [19], in this survey, nearly one third of the participants considered cure or treatment completion only taking into account the nail clinical features (clinical cure). We believe that this is a very high percentage, considering that in cases of severe onychomycosis, up to 10% of the nail is likely to remain clinically abnormal, even when mycology indicates a cure of fungal infection [20]. Inspection of the nail may also have limitations in patients with comorbid diseases affecting nails, such as nail unit psoriasis and traumatic nail dystrophy. Nevertheless, a recent survey among dermatologists also agreed on assessing treatment efficacy by clinical judgement of the normal regrowth of the proximal nail [21].

Survey participants were also asked about criteria to define treatment completion; answers were nearly equally distributed between mycologic cure (22%), clinical cure (29%), and complete cure (29%). One possible explanation of this distribution may be that the kind of treatment (topical or oral) was not specified. Overall, topical therapies show lower mycologic cure and complete cure rates than oral therapies; however, oral treatments have more adverse effects [8]. These findings could support the use of a topical antifungal medication until nail plate appearance is normal, and may explain why clinicians are more cautious in prescribing long-term systemic antifungal treatments.

It is important to highlight that cure is not achieved in 20–25% of treated patients [22]. Patient comorbidities, such as immunosuppression or diabetes mellitus, have an impact on treatment efficacy, since potential interactions between both therapies have to be considered. Finally, patient age, treatment compliance, and fungal resistance also have an impact on treatment efficacy [23].

It is important to recognize that this project was based on a survey, the answers rely on respondent expertise, and the recommendations should not be considered as guidelines. All participants were ENS members, mostly dermatologists with extensive experience in onychomycosis. The respondents reported evaluating an average of 296 patients per month, and 26.4% of these patients presented with nail diseases, a higher percentage than the nail disease average seen by dermatologists (10%) [24] in general, reinforcing these study results. However, the composition of the panel (98% dermatologists and no primary care physicians) could be also a potential limitation, and selection bias cannot be excluded. Another possible limitation was the questionnaire length, which might have caused some bias secondary to fatigue and potentially could also explain why only 22.16% of the ENS members invited to complete the survey answered all of the questions.

Nail specialists commonly use microscopic examination and fungal culture to diagnose DLSO, but these methods are often not available in non-specialized environments. Therefore, our survey participants have reported the minimum clinical changes needed to evaluate DLSO in such situations, including the presence of subungual hyperkeratosis, white-yellow-orange subungual scales, and the presence of yellow nail discoloration. Good indicators to define treatment effectiveness include normal appearance and color of the nail, reduction or absence of scales under the nail, and a reduction of onycholysis. In cases of severe DLSO, when there is treatment failure, concomitant diseases or comorbidities, presence of a dermatophytoma, involvement of the nail matrix, or involvement of several/all nails, referral to specialized healthcare professional should be considered.