A case report of a mixed Chaetomium globosum/Trichophyton mentagrophytes onychomycosis

Abstract

Recently, an increasing prevalence of nondermatophyte mold onychomycosis was observed, in which Chaetomium globosum was rarely involved as primary pathogenic agent. Besides this, reports of mixed infection associating a dermatophyte and a nondermatophyte mold have become more frequent. Here, we present a clinical case of a mixed onychomycosis infection of a toenail caused by Chaetomium globosum and Trichophyton mentagrophytes. To our knowledge, this specific association is reported for the first time in Canada.

1. Introduction

Over the past years, onychomycosis was considered as a fungal nail infection mainly caused by dermatophytes, sometimes yeasts and uncommonly by nondermatophyte molds (NDM) [1]. Then, an increasing prevalence of NDM onychomycosis was observed, Chaetomium globosum identified next as a rare primary pathogenic agent [2]. It is now generally accepted that NDMs account for 2–12% of onychomycosis [3] and reports of mixed infections associating a dermatophyte and a NDM have become more and more frequent, especially with toenail infections and in elderly individuals [4].

Mold species usually isolated in a mixed onychomycosis infection are Scopulariopsis brevicaulis, Fusarium sp, Acremonium, Aspergillus sp, Scytalidium sp and Onychola Canadensis [5]. Most of the time, the identified associate dermatophyte is Trichophyton rubrum [6]. Here, we report a clinical case of a mixed onychomycosis infection of a toenail caused by Chaetomium globosum and Trichophyton mentagrophytes.

2. Case

A 66-year-old man complained about painful dystrophic nail of the right first toenail. On examination, the nail plate showed a well confined spot of yellowish-brown coloration, scattered brown-black punctuations, hyperkeratosis, onycholysis and chronic paronychia of lateral nail fold. (Fig. 1). He did not recall when the problem began.

Fig. 1.

Distal and lateral subungual onychomycosis.

The patient's medical history included chronic schizophrenia, obesity, diabetes type 2, myocardial infarct and cerebrovascular disease. He used to walk barefoot with a dragging foot secondary to a previous stroke. He was living in a damp and dark basement made of sheetrock and wood materials, in very poor hygienic conditions.

On November 2010 (Day 0), nail clippings and scrapings from the hyperkeratosic undersurface of the nail plate were sampled for Calcofluor examination and culture onto both Sabouraud dextrose agar (SDA) and inhibitory mold agar (IMA) test tubes, incubated at 30 °C for 4 weeks. The Calcofluor test showed hyphae and Chaetomium sp was isolated and identified at the Laboratoire de santé publique du Québec.

One month later (Day 30), the same procedure was repeated and yielded Chaetomium sp and Trichophyton mentagrophytes as well. Microscopic examination of culture mounts from positive test tube revealed black globose perithecia, tortuous perithecial hairs and dark septated hyphae. Hyaline hyphae with probable microconidiae were also observed. The patient was examined again in search of fungal skin infection. Tiny and few dead skin debris were found between the first and second toes. The sampled material was too scanty for Calcofluor but culture gave a negative result.

Then, a third nail sampling was done and the result yielded Chaetomium sp only (Day 150). Upon request, the Laboratoire de santé publique du Québec identified the mold at the species level as Chaetomium globosum, using ITS sequence analysis method (the case isolate was deposited at the Laboratoire de santé publique du Québec under accession number LSPQ-00972).

On Day 180, the patient was offered a continuous three months terbinafine regimen (250 mg/day). Pain disappeared after one month and normal nail growth was observed during the following months (Fig. 2). A sample taken twelve months after treatment initiation was negative for both Calcofluor and culture.

Fig. 2.

Twelve months after initiation of treatment.

3. Discussion

On the clinical and epidemiological plan, this distal and lateral subungual onychomycosis (DLSO) case presents many features found in a NDM or a mixed onychomycosis infection: age, gender, diabetes, repeated nail trauma, altered neurologic and circulatory status of the extremities, periungual inflammation and living environment. Chaetomium globosum, as an ubiquitous and cosmopolitan mold, has long been considered as a nail contaminant. However, recent evidences suggest that it could also act as a primary pathogenic agent [7–10].

The presence in the second sampling of Trichophyton mentagrophytes in addition to Chaetomium globosum could suggest Chaetomium as a contaminant and a diagnosis of dermatophyte onychomycosis [11] while the sole detection of Chaetomium globosum in both first and third sampling would rather support the occurrence of a NDM onychomycosis. Indeed, such discordant findings in these three consecutive samplings markedly underscore the need for repeated samplings to confirm either a NDM or a mixed onychomycosis infection, thus satisfying Koch's first postulate at the same time, particularly since contaminant fungi are rarely isolated repeatedly [12,13].

The ecological interactions between dermatophytes and nondermatophytes in mixed onychomycosis infection are complex and not well understood. Nevertheless, Richard C. Summerbell has proposed a useful frame of analysis to differentiate nondermatophytes as colonizers (transient saprophyte or persistent secondary) or invaders (successional or primary), therefore allowing more efficient and specific pharmacological approaches [14]. There is also evidence for coexistence of toenail onychomycosis with other dermatomycoses, especially tinea pedis [15]. Some authors state that tinea pedis almost always precedes onychomycosis and consider the foot as a fungus reservoir [16].

While microscopic examination and culture remain the gold standard in medical Mycology, the underlying pathogenic organisms and pathological pathways could have been further investigated by nail immunohistopathology, PCR-restriction fragment length polymorphism analyses and nested PCR. However, the use of such diagnostic tools is precluded in a daily medical practice. Nevertheless, one could hypothesize a subclinical tinea pedis or, less probably, a superficial white onychomycosis (SWO) caused by Trichophyton mentagrophytes, later transformed into DLSO by Chaetomium globosum, behaving as a successional invader in both cases.

Conflict of interest statement

There are none.