Australas J. Dermatol 1992; 33: 159-163

DERMATOPHYTE AND NON-DERMATOPHYTEONYCHOMYCOSIS IN SINGAPORE

JOYCE TENG-EE LIM, HOCK CHENG CHUA AND CHEE LEOK GOHSingapore

SUMMARY

Onychomycosis is caused by dermatophytes, moulds and yeasts. It is important to identifythe non-dermatophyte moulds as they are resistant to the usual anti-fungals. A prospectivestudy was undertaken in the National Skin Centre, Singapore to study the pattern ofdermatophyte and non-dermatophyte onychomycosis. 53 male and 47 female patients seenbetween June 1990 and June 1991 were entered into the study. Direct microscopy was doneand the nail clippings were cultured. Toe and finger nails were equally infected.Dermatophytes were isolated from 21 patients namely, T. rubrum (12/21), T. interdigitale(5/21), T. mentagrophytes (3/21) and T. violaceum (1/21). Candida onychomycosis occurredin 39 patients and was caused by C. albicans (38/39) and C. parapsilosis (1/39). 37/39patients had associated paronychia. 5 types of moulds were isolated from 12 patients,namely Fusarium species (6/12), Aspergillus species (3/12), S. brevicaulis (1/12),Aureobasilium species (1/12) and Penicillium species (1/12). Although the clinical patternand microscopy may predict the type of organisms, in practice this is difficult. Only cultureswere confirmatory. 28% (28/100) had negative cultures despite a positive microscopy, andmoulds (12/100) grown might be contaminants rather than pathogens.

Key words: Moulds, yeasts, fungi, tinea, onychomycosis, dermatophyte, non-dermatophyte

INTRODUCTION

Onychomycosis, a common nail disorder, iscaused by dermatophytes, non-dermatophytemoulds, or yeasts. Mixed infections have beenreported but are rare. The incidence ofonychomycosis due to dermatophyte or non-dermatophyte varies from place to place. Theroutine incorporation of cycloheximide inmycological media which inhibits the growth ofmoulds may explain the low incidence in somereports. The incidence of these organisms causingonychomycosis in Singapore is unknown. Wecarried out a prospective study to determine thepattern of dermatophyte and non-dermatophyteonychomycosis in patients attending the NationalSkin Centre in Singapore.

Joyce Teng-Ee Lim, MBBS (Malaysia), MRCP (Ire), FAMS.Senior Registrar, National Skin Centre, Singapore.

Hock Chengh Chua, MBBS (Australia). Visiting Fellow.Currently Dermatology Trainee, Perth, Australia.

Chee Leok Goh, FAMS, MMed (Singapore), MRCP (UK).Medical Director and Clinical Professor, National SkinCentre, Singapore.

Address for correspondence: Dr J. Lim, National Skin Centre,1 Mandalay Rd, Singapore, 1130.

METHODS AND MATERIALS

100 consecutive patients, seen in our centrebetween June 1990 and June 1991, with a newclinical diagnosis of onychomycosis were includedin the study. Diagnosis was confirmed by thepresence of fungal elements (mycelium,arthrospores and yeast) on direct microscopy ofnail and subungal scrapings dissolved with 30%potassium hydroxide. Only patients with apositive microscopy were included in the study.Patients with skin disorders causing onychodys-trophy or patients with chronic mucocutaneouscandidiasis were excluded from the study. Thepatients' demographic data were recorded. Theduration, symptoms, characteristics and locationof the onychomycosis were recorded.

Scrapings from nails and nail beds were put in30% potassium hydroxide for microscopy. Nailclippings from all patients were dissolved in 30%potassium hydroxide overnight and inoculatedinto two types of media. Where more than onesite was involved, the specimens were pooled.Mycobiotic agar (Difco Laboratories, Michigan,USA) was used for growing dermatophytes andit contained Bacto-Soytone (lOg/1), Bacto-

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JOYCE TENG-EE LIM, HOCK CHENG CHUA AND CHEE LEOK GOH

Dextrose (lOg/1), Bacto-Agar (15g/l), Actidione(0.5g/l) and Chloromycetin (0.05g/l). ModifiedSabouraud Agar (Difco Laboratories, Michigan)containing Bacto-Neopeptone (lOg/1), Bacto-Dextrose (20g/l), Bacto-Agar (20g/l) andChloromycetin (0.05g/l) was used to culture non-dermatophytes. All cultures were incubated atroom temperature (ZS C to SO^C). The cultureswere examined on the 3rd, 6th, 9th and 12th day.Morphology of fungi colonies and growthcharacteristics were recorded. Cultures were againexamined at six weeks for slow-growers. Nogrowth at six weeks was considered negative.

Positive cultures were confirmed and identifiedby wet mounts and/or slide cultures whennecessary. Candida species isolated were identi-fied using germ tube production, morphology oncornmeal media and mycotube identificationsystem ("Mycotube" Roche). Thex^ test was usedfor statistical analysis. P values ^^0.05 wereconsidered significant.

RESULTS

100 patients (53 male and 47 female) wereincluded in the study. Their ages ranged from 3years to 79 years, with a mean age of 45.2 years.The majority were adults from the third to thefifth decade. Figure 1 shows the age distributionof the patients and the type of organismscultured. There were 68% Chinese, 21% Indians,8% Malays and 3% comprising the otherminority racial group. The racial composition ofthe general dermatological patients attending theCentre during this time was 76.4% Chinese, 9.5%Indians, 8.6% Malays and 5.6% others. Therewere no significant differences in the incidenceof infection in the different races, when comparedto the general dermatological population. Figure

NUMBER OF PATIENTS

0-9 10-19 20-29 30-39 40-49 50-59 60-69 70-79

AGE GROUP

FIGURE 1—Culture Results of Onychomycosis according toage group

Dermatophyte Negative

NUMBER OF PATIENTS

I Chinese [sEJ Malay I . I Indian

FIGURE 2—Culture Results of Onychomycosis according torace.

FIGURE 3—Type of Organism Causing Onychomycosisaccording to sex

2 shows the racial distribution and the organismscultured. Onychomycosis was seen in all theoccupation groups. However, 66% of the femalepatients were housewives doing wet work.

50/100 patients had onychomycosis for morethan two years, 5/100 patients for less than amonth and the remaining (45/100) had theinfection from between 1 to 24 months. 66/100patients presented because of deformity ordyschromia of their nails. The others had pain(16/100), itch (13/100) or both (5/100). The totalnumber of nails involved varied from less than5 nails (57/100 patients) to more than 15 nails(10/100 patients). Onychomycosis involved thefinger-nails in 43/100 patients, the toe-nails in35/100 patients and both finger and toe nails in22/100 patients.

28% (28/100) had a negative culture despite apositive microscopy. Table 1 shows the type of

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TABLE lType of Organism Cultured by Site

DermatophytesT. interdigitaleT. rubrumT. mentagrophyteT, violaceum

MouldsS. brevicaulisAureobasidiumFusariumAspergillusPenicillium

CandidaC. albicansC. parapsilosis

Finger Nails

28

—1

——2——

341

Toe Nails

493—

11531

111

Total

61731

11731

452

organisms cultured and the site. Dermatophytescaused infection in 21/100 of the patients (Figure3), and only four species were cultured. Thesewere T. rubrum (12/21), T. interdigitale (5/21), Tmentagrophytes (3/21) and T. violaceum (1/21).Those patients who had T. mentagrophytesinfection had no animal contact and no zoophilicinfection on another part of the body. As thezoophilic variety is unusual in toe nails and thesepatients had no sign of zoophilic infection else-where, we assumed that they might be ananthropophilic variety, the variety not identified.12/21 of these patients had associateddermatophyte infection elsewhere and the samespecies of clermatophyte were cultured from theskin sites. 39/100 had Candida onychomycosisand these were caused by 2 species namely, C.albicans (38/39) and C parapsilosis (1/39). Allbut 2 patients with Candida onychomycosis hadassociated paronychia. 12/100 had a positiveculture for non-dermatophyte mould. Themoulds isolated were namely, Fusarium species(6/12), Aspergillus species (3/12), S. brevicaulis(1/12), Aureobasidium species (1/12) andPenicillium species (1/12).

Dermatophyte onychomycosis affected moremale patients whereas Candida onychomycosiswere common in female patients (Figure 3).Mould onychomycosis affected both male andfemale patients equally. However, moulds werenot recovered from the two extremes of ages(Figure 1). There was also no difference in thetype of organisms recovered from the differentraces (Figure 2).

DISCUSSION

Onychomycosis in children is uncommon', witha prevalence rate of from 0.2% to 0.6% in thegeneral population.^' When it does occur theparents may act as the source of infection.^ Theusual organism isolated is T. rubrum. However,one of our children had Candida onychomycosis.This is uncommon in children unless it occurssecondary to an underlying nail or systemicpathology. Our patient had no such predisposingfactors but her mother had a similar conditionsuggesting that she could have been the sourceof infection. 95% of our patients were adults con-curring with reports that onychomycosis is anadult disorder.^'

Onychomycosis is a chronic disorder and isoften resistent to treatment. Our study concurredwith this. Patients are usually asymptomatic anddo not seek treatment, another reason for thechronicity of the infection. The presentingcomplaint in our study was cosmetic, noted in aprevious report.'

Dermatophyte onychomycosis usually starts inthe toe-nails, especially the big toes.* Candidaonychomycois, in contrast, affects the finger-nailsearly. In our findings, the initial site of infectionwas not predictive of the causative organisms, asCandida had been isolated from toe-nails aloneand dermatophytes from finger-nails alone.

Zaias^ divided onychomycosis into four clinicaltypes namely, distal subungual onychomycosis(DSO), proximal subungal onychomycosis (PSO),superficial white onychomycosis (SWO) andCandida onychomycosis. The majority of ourpatients (30/100) had total subungal onycho-mycosis and it was difficult to determine theclinical type. One patient had SWO of the toe-nail caused by T. interdigitale, which was alsoreported to be the commonest dermatophytecausing this infection."^ PSO, the rarest clinicaltype, was present in 2 of our patients. Bothaffected the toe-nails and was caused by T.rubrum. However, morphology was not apredictive feature to differentiate dermatophytefrom non-dermatophyte onychomycosis in ourpatients, except for the presence of paronychiawhich tended to suggest a diagnosis of Candidaonychomycosis.

The positive culture rate in onychomycosis,even in the presence of positive direct microscopy,varies from 30 to 50%.' * Therefore, methodslike suction drill sampling*' have beensuggested to increase the yield. Other authors

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JOYCE TENG-EE LIM, HOCK CHENG CHUA AND CHEE LEOK GOH

have used scanning electron microscopy'" to helpmake the diagnosis. Dermatophyte onycho-mycosis is commonly due to T. rubrum, T. menta-grophytes and E. floccosum.'" '^ Four typesnamely T. rubrum, T. interdigitale, T. menta-grophytes and T. violaceum were isolated in ourstudy. There was no infection by E. floccosum asthis was not a common cause of tinea pedis inSingapore. The commonest dermatophyte recov-ered was T. rubrum, which is also the commonestdermatophyte reported previously."'^ ' Derma-tophyte onychomycosis occurred in all age groupsand was more common in male than femalepatients, as is reported els where.""'

Candida onychomycosis occurs in threepatterns,"* namely (a) associated with chronicmucocutaneous candidiasis, (b) associated withparonychia and lateral onycholysis and (c)associated with primary distal and lateralonycholysis. The majority of our patients (37/39)had associated paronychia suggesting that the nailinfection was secondary to Candida paronychia.However, in two patients paronychia was absentand there was also subungual hyperkeratosissuggesting that the onychomycosis was a primaryevent. It is important to differentiate betweenthese two types as it has been reported that thelatter pattern responds poorly to topicalagents.""' The organisms responsible for theonychomycosis were C. albicans and C.parapsilosis. Our findings concurred withprevious reports that Candida onychomycosis ismore common in females and affects finger nailsmore."" Those with toe-nail infections hadconcomitant finger-nail infections, which prob-ably explained the relatively high numbers of toe-nail Candida onychomycosis in our study. Theinfection was uncommon in the extremes of agewhere wet-work and hence paronychia was lessof a problem.

Onychomycosis due to moulds has beenreported to occur on dystrophic nails and henceto have a higher incidence in older patients.' 'Our study showed that it was common in thesecond to the fifth decade, with no cases in theextremes of age. The toe nails were affected in allcases, concurring with previous reports.'^'' Intwo patients their finger nails were infected inaddition to their toe-nails. Moulds reported tocause onychomycosis include Aspergillusspecies,"" Fusarium species,"" Hendersonulatoruloidea,^" S. brevicaulis^' and others.""" S.brevicaulis, Aureobasidium, Fusarium spp..

Aspergillus spp. and Penicillium were isolated inour study. It was felt that Aureobasidium andPenicillum were contaminants as the cultures werenot reproducible. The other moulds wereconsidered to be significant using the criteriasuggested by English; that is, positive microscopyand repeated cultures without isolation ofdermatophytes.

Six of our patients had Fusarium onycho-mycosis. Although normally known as a skincontaminant, Fusarium had been reported tocause fungal keratitis," superficial onychomyco-sis" and even osteomyelitis.^' The commonestspecies reported to cause disease was F.oxysporum. We were unfortunately unable toidentify the species.

This study showed that onychomycosis inSingapore is caused by either dermatophytes(21%) or yeasts (39%). Moulds (12%) are anuncommon cause. Moulds are resistant to thecommonly used anti-fungal agents and hencetheir identification is important in preventingsuch medications from being prescribed. Methodsused to distinguish them include the clinicalpattern and site of infection. For example PSOhas not been documented to be caused by mouldand yeasts. Microscopy may help as some mouldshave a fronded appearance. Their hyphae arehyaline, have a more variable width, swollen ordistorted^" and in some may be pigmented orappear double-contoured.^' Although available,these measures are usually not helpful in thechnical situation. Theref'ore, culture mediawithout cycloheximide is used if non-dermatophytes are suspected. The significance ofany non-dermatophyte isolated must beconfirmed by isolating the organisms in 5 out of20 inocula without concomitant isolation of anydermatophytes (as suggested by Enghsh'O.

ACKNOWLEDGEMENT

We would like to thank Mr Kamarudin bin Aliand Mr Koh Mong Teck for their technicalassistance.

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