Clinicomycological and Histopathological Profile of Onychomycosis: A Cross-sectional Study from South India.

BACKGROUND: Onychomycosis (OM) is a fungal infection of the finger or toenails caused by dermatophytes, yeasts, or nondermatophyte molds (NDMs) and can involve any component of the nail unit. OM, apart from being asymptomatic, is a chronic disease and warrants long-term treatment. AIMS: The aim was to study the clinicoepidemiological features of OM and to evaluate the mycological and histopathological features among patients attending the dermatology outpatient department. SUBJECTS AND METHODS: A cross-sectional hospital-based study was performed in 500 patients with symptoms related to the nails and nail folds. OM was confirmed in 284 patients by potassium hydroxide (KOH) mount, fungal culture, or biopsy. Descriptive analysis of the data was undertaken.
RESULTS: The study included 284 confirmed cases of OM of which 117 (41.1%) were positive for fungal elements by KOH mount, 168 (59.1%) samples showed positivity in fungal culture, and 62 (21.8%) samples had positive nail biopsy results. Distolateral subungual OM was the most common clinical type (47.6%). Among the fungal isolates, a predominance of dermatophytes was observed followed by yeasts and NDMs. The most common dermatophytic fungal isolate in the culture was Trichophyton rubrum (45%).
CONCLUSION: Our study implies the importance of laboratory diagnosis of OM as it can mimic diverse nail disorders. As the role of NDMs and yeasts is on the rise for etiology of OM, investigations such as KOH examination, culture, or nail biopsy becomes essential for correct diagnosis and management.

Introduction

Onychomycosis (OM) is described as the fungal infection of the nail plate with dermatophytes, nondermatophytes, or yeasts. It affects approximately 5% of the population worldwide,[1] and the prevalence in India is reported to vary from 0.5% to 5%.[23] OM accounts for about 50% of onychopathies and 30% of mycotic cutaneous infections.[45] The risk factors such as regular use of occlusive footwear, present-day lifestyle, and immunocompromised disease states contribute to its increased incidence. It usually affects individuals in their thirties to sixties with increased incidence among males. The diagnosis of OM is made clinically and can be confirmed by potassium hydroxide (KOH) examination, fungal culture, and/or nail plate biopsy.

Although encountered as a common problem, recent clinical and mycological studies on this context are still lacking. OM has a chronic course and demands long-term treatment. There is an emerging importance of laboratory studies such as KOH mount, culture, and histopathology of the nail plate for definitive diagnosis of OM for prompt diagnosis and management. In view of this, our study was conducted to evaluate the clinical patterns as well as the mycological profile and histopathological changes in patients with OM.

Subjects and Methods

A total of 500 consecutive patients with symptoms related to the nails and nail folds attending the dermatology outpatient department of our institute, a tertiary care teaching hospital, in south India during November 2015–May 2017 were evaluated. Of the 500 clinically suspected cases, 284 patients were confirmed as OM either by KOH, fungal culture, or by biopsy. Patients who were on topical and/or systemic antifungal therapy for the past 3 months were excluded from the study.

After obtaining informed consent, the demographic data and detailed history with particular emphasis on the history of trauma, infections, occupation, diabetes mellitus, and personal habits were taken, and all the details were noted in a prestructured pro forma. The morphological types of OM were documented as distal lateral subungual onychomycosis (DLSO), proximal subungual onychomycosis (PSO), superficial white onychomycosis (SWO), total dystrophic onychomycosis (TDO), endonyx, and DLSO/TDO overlap. All the patients were examined for evidence of other cutaneous fungal infections or coexistent cutaneous diseases. Nail clippings were taken from the affected parts of the nails. The affected nail was meticulously swabbed with 70% alcohol, and the distal free edge of the nail plate along with any attached subungual debris was clipped. Nail clippings were separated in two equal parts: one for KOH examination and one for fungal culture. The culture sample was wrapped carefully in a sterile black paper. The sample for KOH mount was treated with 20% KOH for 24 h and was examined under low- and high-power light microscope for the presence of fungal mycelia and spores. The nail material for fungal culture was inoculated in Sabouraud peptone–glucose agar with cycloheximide, chloramphenicol, and gentamicin for 2–4 weeks. The nail sample for histopathology was harvested using 3-mm sterile punch and was placed in a standard skin biopsy specimen container with 4% formaldehyde and was subjected to histopathological examination and periodic acid–Schiff (PAS) staining for the identification of fungal elements.

Results

The study population comprised of 284 patients with 96 males (33.8%) and 188 females (66.2%). The age of the patients ranged from 22 to 78 years. The mean age was 41.73 ± 9.5 years. The female-to-male sex ratio was 2:1, indicating a female preponderance. The most common occupation noted among our study participants was farming (46.6%), followed by homemakers associated with wet work (31.2%). About 86 patients (29.9%) were using occlusive footwear for prolong duration. Fungal infection elsewhere in the body was found in 51 (18%) patients. DLSO was the most common morphological variant seen in 135 (47.6%) patients [Figure 1]. Thirty-eight patients (13.4%) were clinically classified as TDO [Figure 2], DLSO, and TDO overlap in 97 (34.1) cases, six cases each (2.1%) as PSO and SWO, and two cases (0.70%) as endonyx. About 78 (27.5%) of the patients in the study population were found to be diabetic, which was found to be the most common systemic disease to be associated with OM. This was followed by hypertension which was seen in 11.5% of individuals. The other systemic diseases included venous dermatitis and varicose ulcers (5.5%), psoriasis (5.1%), and chronic kidney disease (2.5%). Among the 284 confirmed cases of OM, 117 (41.2%) were positive for fungal elements by KOH mount [Figure 3]. Fungal culture was positive in 168 (59.2%) patients, and 62 (21.8%) had nail biopsy results positive for fungal elements. Among 117 KOH-positive cases, 17 (14.5%) were positive for nondermatophytes. Both culture and KOH positivities were seen in 63 (22.1%) samples. Among the culture-positive cases, the common fungal isolates were dermatophytes (132, 78.6%), followed by nondermatophyte molds (NDMs) (16, 9.5%) and yeasts (20, 11.9%) The diagnosis of nondermatophytes was confirmed by the following criteria: (1) the presence of fungal elements in the KOH mount of nail scraping, (2) the same fungal growth in three consecutive cultures taken 3 weeks apart; and (3) nongrowth of dermatophytes or yeasts in three culture specimens. The dermatophyte frequently isolated was Trichophyton rubrum (76, 45.0%) [Figure 4], followed by Trichophyton mentagrophytes (45, 26.7%) [Figure 5]. Among the nondermatophytes, Aspergillus niger (10, 6.10%) [Figure 6] was predominant and yeast isolates included Candida albicans (17, 9.92%) and Candida parapsilosis (3, 1.50) [Table 1]. Biopsy of nail plate for histopathology was done in 62 nail samples. The conclusive finding was linear thread-like fungal elements (68%) and red dot-like structures (32%) [Figure 7], and both the findings were considered to be positive for OM.

Figure 1

Distal and lateral subungual onychomycosis – yellowish-white discoloration with onycholysis

Figure 2

Total dystrophy of the nail plate

Figure 3

Thin septate hyphae suggestive of onychomycosis under potassium hydroxide mount light microscope (×40)

Figure 4

Lactophenol cotton blue mount showing microconidia along sides of hyphae suggestive of Trichophyton rubrum (×10)

Figure 5

Microscopic appearance of Trichophyton mentagrophytes showing spiral hyphae and numerous microconidia (Lactophenol cotton blue, ×10)

Figure 6

Microscopic image of Aspergillus niger showing jet black conidia covering the entire surface of the vesicle (×10)

Table 1

Fungal isolates in culture

Fungus	Total (n=168), n (%)
Trichophyton rubrum	76 (45.2)
Trichophyton mentagrophytes	45 (26.8)
Trichophyton interdigitale	6 (3.5)
Trichophyton verrucosum	4 (2.4)
Epidermophyton floccosum	1 (0.6)
Aspergillus niger	10 (6.0)
Fusarium spp.	6 (3.6)
Candida albicans	17 (10.1)
Candida parapsilosis	3 (1.8)

Figure 7

Histopathology of nail plate (H and E, ×40) showing fungal elements as red dots, identified with blue arrow

Discussion

OM is a chronic mycotic infection of the finger and toenails that can have a prominent impact on patients’ quality of life. The prevalence of OM has been reported to increase with advancing age. About 15%–20% prevalence is seen in patients aged 40–60 years, and the frequency rises in those over 60 years of age.[6] In our study, the peak incidence was seen in the age group of 31–45 years (39.3%). This is perhaps due to occupation-related trauma and prolonged wearing of occlusive shoes in young population. A similar observation of predominance of patients in the younger age groups has been reported in different studies from western countries[7] as well as from India.[891011]

In our study, OM was more common among females (66.2%) than in males (33.8%). These results are in accordance with many of the previous literature.[1213] The remarkable female preponderance in the study can be attributed to more pronounced wet work among females. The mean duration of the disease was 4.8 years, which was significantly lower than that of 8–12 years, reported in different studies.[141516] Systemic diseases such as diabetes were associated in 27.5% of cases in the present study and hypertension in 7.6%. Diabetes is a known risk factor for OM predominantly due to its effect on microcirculation and immunosuppression. A similar association has been found in studies conducted in India and in western countries.[171819]

Direct smear with KOH is the simplest, most rapid, and inexpensive method for the diagnosis of OM. However, the results of the KOH smear depend on the physician's interpretation, particularly in cases of low visibility of scant fungal material in the nail plate. In our study, about 117 (41.2%) samples were positive for fungal elements by KOH mount. It is not useful for identifying the fungal species or determining the viability of the organism. Fungal culture is a highly specific method and can identify causal organism. Fungal culture positivity in the current study was seen in 168 (59.1%) samples. Among the culture-positive cases, dermatophytes were most commonly encountered (78.6%), which is comparable to other studies.[202122] Among the dermatophytes, T. rubrum (45.0%) was top in the list followed by T. mentagrophytes (26.7%). T. rubrum has been reported as the most prevalent dermatophyte isolated in south Indian studies,[202122] whereas certain studies from north India showed a high prevalence of T. mentagrophytes.[2123] Among the nondermatophytes, Aspergillus species (6.10%) was predominant in our study which was in accordance with other studies conducted in India and abroad.[202122] C. albicans is reported as the most common cause of paronychial OM.[8] This is reflected in our study where all the paronychia cases grew C. albicans on culture. Histopathological evaluation of nail samples with PAS staining has a better sensitivity when compared to KOH and culture and has been considered a complementary method for the diagnosis of OM. The nail histopathology for OM was positive in 62 nail samples in our study. The presence of fungal elements in the nail plate was observed as thread-like pink structures (68%) and red dots (32%) in the histopathology (HPE) sections. Similar findings were observed in the literature.[24]

Among the clinical types of OM, DLSO was the most prevalent clinical type (47.6%), which is in accordance with published literature.[222325] TDO was the second most common type of OM (13.4%) which was also reported by Jesús-Silva et al.[26] PSO was seen in 2.10% of our study population; however, a greater prevalence has been reported by some researchers,[1011] while others have reported a lower prevalence.[927] PSO in our study was not associated with any immunodeficiency disease, contrary to available reports.[2127]

Limitations of the study

The nail histopathology could not be performed in majority of the patients due to cosmetic concern and financial issues.

Conclusion

OM is no longer considered to be a mere problem as it affects the physical appearance and occupational opportunities of affected persons, thus impairing the quality of life. This study emphasizes the importance of fungal culture and species identification as it helps in selecting appropriate antifungal agent for complete cure of the disease. Culture may not be feasible for every patient with OM, but performing culture of nail plate in doubtful cases helps in the correct diagnosis and management.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.