Great toenail onychomycosis caused by Syncephalastrum racemosum
Department of Dermatology1 and Institute of Microbiology, Division of Medical Mycology2, Military Medical Academy, Belgrade, Serbia and Montenegro. firstname.lastname@example.org
Nondermatophyte molds are fungi found in soil and decaying plant debris and are generally considered to be uncommon or secondary pathogens of diseased nails. Prevalence rates of onychomycoses caused by nondermatophyte molds range between 1.45 percent and 17.60 percent. The most common nondermatophyte molds associated with nail disease are Scopulariopsis, Scytalidium, Fusarium, Aspergillus and Onychocola canadensis. Syncephalastrum racemosum, a nondermatophyte mold, belongs to the class Zygomycetae. Only one well-documented case of human disease attributed to this organism has been described. We describe a 45-year-old man with culture proven toenail onychomycosis due to Syncephalstrum racemosum.
Nondermatophyte molds are fungi with known habitats mostly in soil and decaying plant debris. They have been traditionally regarded as uncommon or secondary pathogens of already diseased nails . Prevalence rates of onychomycoses caused by non-dermatophyte molds range between 1.45 percent and 17.60 percent . The variation in incidence might be a consequence of geographic differences in mold distribution or diagnostic methods. A recent United States epidemiological surveillance registered a decline in the incidence of nondermatophyte mold toenail onychomycoses . The most common nondermatophyte molds causing nail disease are Scopulariopsis, Scytalidium, Fusarium, Aspergillus and Onychocola canadensis [1, 2]. The criteria for diagnosis of nondermatophyte mold infections of the nail need to be stringent. Typical hyphal structures of causative fungi should be seen by microscopic examination of potassium hydroxide (KOH) mounts, and there should be repeated isolation of the suspected organism on two or more separate occasions (from samples taken at different time points) in the absence of any growth of a dermatophyte [1, 2]. Alternatively, a count of 11 or more culture-positive inocula out of 15 planted (in combination with a positive KOH result) has a strong statistical correlation with the likelihood that the nondermatophyte is the etiologic organism .
A 45-year-old man presented with a discolored and thickened right great toenail. About 7 months before the consultation he had injured the nail during a soccer game. A small patch of subungual hematoma was a consequence of the injury. A few months later, subungual hyperkeratosis, yellowish discoloration, and onycholysis developed. Nail clippings and subungual debris were taken for mycological examination. Meanwhile, the patient sought a consultation of a general surgeon who surgically extirpated the nail plate and sent it to the same laboratory. KOH mounts were prepared from original scrapings, scrapings taken from the dorsal and ventral sides of the extirpated nail plate as well as from the finely chopped nail plate clippings taken on both occasions. The nail fragments were also seeded on Sabouraud dextrose agar slopes with and without cycloheximide. The cultures were incubated at 27°C. Microscopic examination of the initial and scrapings from the ventral surface of the extirpated nail plate revealed wide, ribbon-like hyphae in masses, typical for Zygomycetae, and fruiting bodies similar to Aspergillus species (Figs. 1 and 2). The presumptive diagnosis of Syncephalastrum racemosum infection was made. The diagnosis was confirmed by culture growth on Sabouraud dextrose agar without cycloheximide. The abundant, erected mycelium, 0.5-cm tall was seen in 3 days. The surface color of the colony was at first yellow; after a few days the center turned black. Microscopic examination of the colony showed wide hyphae with sparse septae. Sporangiophores terminated in swollen vesicles with radial merosporangiae filled with spores. There was no growth on the Sabouraud agar supplemented with cycloheximide. After the surgery, the patient applied nystatin ointment b.i.d. to the exposed nailbed for two weeks. A healthy nail plate grew out and remained disease free for more than 4 years.
Syncephalastrum racemosum is a ubiquitous, saprophytic fungus that has been isolated from environmental sources worldwide. It belongs to the class Zygomycetae . The only well-documented case of Syncephalastrum infection, described by Kamalam and Thambiah, began as skin involvement on the finger and progressed to osteomyelitis . The organism has been isolated readily from normal fingernails and toenails of Egyptian students with no signs of actual disease caused by the fungus . S. racemosum is generally seen as clinical contaminant . Typical fruiting bodies and ribbon-like hyphae in the nail plate of our patient, along with the same microscopic morphology of the cultured fungus, were consistent with S. racemosum. The same findings obtained at two different time points in the absence of dermatophyte growth strongly suggest that S. racemosum is a causative agent of nail disease in the patient.
Preceding nail trauma is a known predisposing factor for nondermpatophyte-mold onychomycosis [1, 2]. It is important to note that the fruiting bodies of S. racemosum and Aspergillus flavus are similar in direct KOH mounts but the hyphal morphology (aseptate, ribbon-like mycelium) and the merosporangial sack surrounding the sporangiospores in Syncephalastrum cultures is crucial for distinguishing the two fungi . Surgical nail plate avulsion along with topical nystatin were sufficient to cure the infection and enable regrowth of the normal nail. It is clear that regardless of the pathogenic potential to humans, all classes of fungi can cause nail disease, especially in traumatized nails. Accurate mycological diagnosis is of great importance for the management of the onychomycoses.
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