Clinico-mycological study of onychomycosis

INTRODUCTION

Onychomycosis is the most common nail infective disorder, caused by dermatophytes, non-dermatophytes and yeasts. It accounts for 30% of cutaneous fungal infections and 50% of nail disorders worldwide.¹ In most cases, this infection is caused by anthropophilic dermatophytes, in particular by Trichophyton rubrum, followed by Trichophyton mentagrophytes var interdigital. The non-dermatophyte moulds (NDMs) like Fusarium spp Aspergillus spp, can be involved in onychomycosis as primary pathogens, as secondary pathogens or as contaminants.² Traditionally, dermatophytes have been predominantly attributed to cause onychomycosis. However, in the recent years, there has been a dramatic increase in non-dermatophyte onychomycosis (NDO), attributed to widespread use of broad-spectrum antibiotics, chemotherapy, and increase in elderly and immunocompromised population. The incidence of NDO is variable across the globe; it’s isolation rates are low in Europe (5%) and United States (20%), however isolation of NDMs are higher in tropical countries of Asia (40.5% to 68%) including India (13.6%-53.33%).^3-9

Thus NDMs, previously considered as mere contaminants have emerged as potential pathogens in the tropical regions, in comparison to the traditional isolate of dermatophytes.¹⁰ In the current study, the demographic data, clinical features and fungal spectrum of patients presenting with onychomycosis was reported. This study was designed to assess the most common pattern of onychomycosis and identify the causative agents.

METHODS

The study was carried out in the outpatient department of St John’s Medical College Hospital, Bangalore, India from September 2010 to September 2012. The climate of this place is tropical savanna type with distinct dry and wet seasons. The inclusion criteria were patients showing nail changes suggestive of Onychomycosis (OM) namely-onycholysis, onychodystrophy, subungual hyperkeratosis, thickening of the nail plate, Discolouration of the nail plate - melanonychia or leukonychia and paronychia which were positive for fungi on direct microscopy using potassium hydroxide. Patients whose nail clippings were negative for fungal elements on direct microscopy and those who had received antifungal treatment on the preceding one-month period were excluded.

Laboratory methods were as follows- the nail specimens were collected according to standard procedure, subjected to mycological study by direct microscopy using potassium hydroxide (KOH) 20% and lactophenol cotton blue preparation. Sabouraud dextrose agar along with chloramphenicol was used for culture. The culture medium was incubated at room temperature and was observed for fungal growth. Culture reading was done every day in the first week followed by every week in the following month. Based upon the colony morphology the fungus was broadly identified as yeast and mould. Yeasts were further identified by morphological tests which are germ tube test and chlamydospore fermentation and biochemical test i.e.; carbohydrate assimilation test and fermentation test. Moulds were further identified as dermatophytes and non-dermatophytes based on preliminary macroscopic and microscopic colony morphology using lacto phenol cotton blue.

Dermatophytes were grown on dermatophyte test medium and slide culture. Based on the size, number, shape and arrangement of conidia they are further identified as Trichophyton, Epidermophyton and Microsporum. Speciation of Trichophyton was done using trichophyton agar and invitro hair perforation tests. The moulds were identified to species level based on colony morphology and slide culture technique. The clinical and mycological findings were recorded and correlated. Data were analysed using SPSS statistics for Windows, version 17.0 (SPSS Inc, Chicago, IL, USA) Chi-square test was the statistical method used for analysis of data.

RESULTS

A total of 100 patients were enrolled in the study, whose age ranged from 19 to 85 years and the mean age was 43.86 years. Among the study patients 62(62%) were males and 38(38%) were females. Among the 62 males, 45% had toenail and 38% fingernail involvement. Among the 38 females, 47% and 44% had finger and toenail involvement respectively (Table 1).

The thumb and the great toe were most commonly involved in the upper and lower limb (Table 2).

Distal and lateral subungual onychomycosis (DLSO) was the most common form of onychomycosis seen (70%) followed by, total dystrophic onychomycosis (TDO) 11%, mixed onychomycosis (MO) 11%, chronic paronychia (CP) 6%, subungual onychomycosis (SO)1% and proximal subungual onychomycosis (PSO)1% Among the 100 nail specimens cultured, 49% showed fungal growth. Among the culture positives, NDMs accounted for 72%, followed by16% dermatophytes and 12% yeasts. Among the NDMs, the distribution was 31% Aspergillus spp (Figure 3), 31% Fusarium spp, 4%, Cladosporium spp, 2% Scytalidium spp and 2% showed dual growth of Aspergillus spp and Scytalidium spp. Among dermatophytes, Trichophyton rubrum (Figure 4) was the only isolate. Among yeasts, Candida albicans (Figure 5) was the only isolate.

DISCUSSION

Among the 100 cases of suspected onychomycosis the male to female ratio was 2:1. This result is comparable to Patwardhan and Perea et al.^7,11 This is probably attributable to outdoor occupation of males, subjecting their nails to higher chances of trauma. The majority of the studied patients were between the ages 18 and 40 yrs. (46%). The higher prevalence in this age group could be secondary to occupation-related trauma and health seeking behaviour. This is in accordance with other studies.^7,12,13 However in developed countries this entity is considered to be an age-related infection that is more prevalent among males in the older age groups.^14,15 A higher toe nail involvement compared to finger nail involvement (Table 1) was noted. Similar findings were noted among several other studies.^4,8,14 This is attributable to slow growth of the toenails, which facilitates the invasion of the fungus and is perhaps supported by factors such as trauma and poor circulation.

Female patients had predominant fingernail involvement (Table 2), attributable to frequent household work. This result is agreeable with other studies.¹⁶ Males had predominant toenail involvement (Table 2), these findings are consistent with other studies.^4,7,11,15 This is attributable to open footwear and exposure to soil saprophytes.

Among the fingernails, the thumb (Table 2) was frequently involved probably due to occupation related trauma and household work.^7,16 Among the toenails, the great toe (Table 2) was most commonly involved, possibly due to its greater size predisposing to more frequent trauma. Similar findings were observed by other authors.^7,14

Fungal cultures were positive among 49% patients and negative among 51% patients. Similar isolation rates were noted by\ Patwardhan et al.⁷ Among culture positive samples, 72% were NDMs, 16% Dermatophytes and 12% were Yeasts. Similar pattern of isolation was noted in recent studies.^5,6,17,18

The presence of superficial fungal infection was seen among seven patients, majority of whom had tinea pedis. T. rubrum was most commonly isolated in this group, which is in accordance with previous studies.^14,15 The use of open footwear was seen among 41 patients among whom NDMs were predominantly isolated. This is attributed to the minimal protection that open footwear offers against the external environment which exposes the nail to soil saprophytes. Similar results were noted in several studies.^17,18

The common clinical pattern of onychomycosis seen was DLSO, followed by TDO, MO, CP, SO and PSO. This finding is in accordance with reports by Garg et al, and Patwardhan et al.^7,13

The isolation pattern of the organisms varied between clinical patterns of OM (Table 4). Thus clinico- etiologic correlation reveals that a single pathogen could give rise to more than one clinical type of OM. Conversely. a given clinical pattern of onychomycosis can be caused by different organisms. Similar findings were noted by other authors.^19-22 Interestingly, periungal inflammation in association with nail dystrophy was a finding noted among OM secondary to NDMs. This finding was noted in several other studies too.^15-17

A high isolation rate of NDMs were noted in our study (72%). Similar high isolation rates are reported from Malaysia (45.4%), Pakistan (68%) Teheran (40.5%), Thailand (51.6%) and Sri Lanka (45.8%).^6,18,23-25 This is in contrast to studies done in temperate countries, where the isolation rates of NDMs varied from 1.49% and 33.5%.^26,27 This variation is a result of geographic differences in mould distribution and humidity. In addition, use of broad-spectrum antibiotics, immunosuppression, occupational trauma and aging population predispose the nails to the invasion of NDMs. Among NDMs the isolation rates of various species vary considerably in different studies. The most common organisms isolated worldwide are Scopulariopsis brevicaulis, Scytalidium dimidiatum, Fusarium spp, Aspergillus spp, and Acremonium spp. The highest isolation rates were of Aspergillus spp (31%) and Fusarium spp (31%) is in accordance to recent case reports and epidemiological studies.^5,26-30

Although study is not a comprehensive epidemiological survey this study demonstrated that 29.3% of onychomycosis cases are due to NDMs, which is 3 times more than the isolation found in the last study conducted in Bangalore, India.¹² The fact that non-dermatophyte moulds is the most common pathogen implicated for onychomycosis in this population, poses a challenge as its response to oral antifungal is unpredictable. The current available antifungal agents are more effective against dermatophytes and yeasts. Avulsion of the effected nail and treatment with oral antifungal may be the best available option in cases of infection with non-dermatophyte moulds.

CONCLUSION

A single pathogen could give rise to more than one clinical type of OM and a given clinical pattern of onychomycosis can be caused by different organisms. The presence of paronychia in association with OM is suggestive of NDM etiology. Although, it is difficult to ascertain the role of NDMs as primary pathogen in deformed nail they should be considered as important pathogens, when evaluating patients with cultures that are negative for dermatophytes, or in those experiencing treatment failures. The results of this study would be very valuable for the dermatologists working in this area, and further epidemiological investigations should be performed in every country in order to determine the fungal species associated with OM.

ACKNOWLEDGEMENTS

Author would like to thank Mr Simon and Mrs Joshila for their assistance in conducting the laboratory investigations.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: The study was approved by the institutional ethics committee

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