Cutaneous hyalohyphomycosis in an immunocompetent host.

Sir,

Hyalohyphomycosis is a rare infection caused by fungi with colorless (hyaline) mycelia. We report a case of cutaneous hyalohyphomycosis caused by Paecilomyces in an immunocompetent host.

A 19-year-old healthy female presented with an asymptomatic erythematous verrucous plaque on the dorsum of her little toe [Figure 1]. The lesion, which had been present for 4 years, had started as a small red papule and gradually extended to form a plaque. The patient could not recollect any history of trauma, thorn prick, or insect bite. Her past medical history was unremarkable. Before presenting to us she had been diagnosed as lupus vulgaris on the basis of histopathology and had taken a 6-month course of antitubercular therapy, but despite this the lesion persisted. A repeat biopsy from the lesion was taken and sent for histopathology and fungal culture. Fungal culture on Sabouraud dextrose agar medium showed floccose, pinkish-mauve colonies. Microscopy of the slide culture revealed erect conidiophores, divergent phialides with elongated tapered necks, and divergent chains of elliptical conidia [Figures 2 and 3]. On the basis of these findings the mold was identified as Paecilomyces. The histopathological report was inconclusive and showed only pseudoepitheliomatous hyperplasia. Since Paecilomyces sp. are known to be contaminants, biopsy for fungal culture was repeated and this grew Paecilomyces again. Hence, even though fungi were not identified on histopathology, the patient was empirically placed on itraconazole 400 mg daily.

Figure 1

Pretreatment photograph showing hyperpigmented verrucous growth on the foot

Figure 2

Culture of the skin biopsy on agar plate showing the filaments of fungi

Figure 3

Microscopy of smear from the culture plate showing divergent phialides and erect conidiophores

Paecilomyces is a saprophytic filamentous fungus, mostly found in the soil and decaying vegetation and as a ubiquitous air-borne contaminant. Fungi belonging to this genus are notorious for their resistance to sterilization and are frequent contaminants in lab cultures. The two major pathogenic species of Paecilomyces are P. lilacinus and P. variotii, with the former causing most of the reported infections. P. lilacinus was originally known as Penicillium lilacinus but was later reclassified as a species of Paecilomyces. It received its name because of its lilac-colored colonies and the production of a deep purplish-red pigment on Czapek solution agar.[1]

The majority of Paecilomyces infections are either iatrogenic or occur in immunocompromised hosts. The eyes are affected frequently, particularly after cataract surgery or intraocular lens implantation. Paecilomyces has also been isolated from cases of postsurgical sinusitis, pleural effusions, and prepatellar bursitis occurring after joint aspiration. Paecilomyces mold grows well on Sabouraud dextrose agar and the organism can be identified within 7-14 days. On tissue sections, PAS-positive Paecilomyces hyphae can be seen, which are morphologically irregular and demonstrate both 45° and 90° branching. Unlike Aspergillus, Paecilomyces may exist in various forms in tissue and exhibit conidia and phialides, often leading to a misdiagnosis of candidiasis before the culture results become available.[2]

Cutaneous infection with Paecilomyces is rare and is most commonly encountered in the setting of immunosuppression. In our case, cutaneous infection was seen in an immunocompetent lady and Paecilomyces infection was proved by culture on two different occasions. An extensive literature search revealed only six reports of cutaneous infection by Paecilomyces sp. in immunocompetent hosts. Among these earlier cases, one had history of previous trauma, three were predisposed to minor injury because of their jobs or hobbies, and one had a history of dog bite. In all these cases traumatic implantation of the organism was most likely responsible for the infection, as was seen in our case.[3]

Although the infection is reportedly difficult to treat, most cases are not fatal. The susceptibility to antifungals varies widely in this genus and correct species identification is therefore imperative. P. variotii is sensitive to amphotericin B, while P. lilacinus is usually resistant to amphotericin B and flucytosine. Currently, there is no standard treatment regimen for cutaneous P. lilacinus infections, though most cases seem to have responded to systemic azole antifungals.[4] Our patient received itraconazole 400 mg daily for 6 months, followed by a combination of itraconazole 400 mg and terbinafine 250 mg daily for 3 months. Mild flattening of the lesion was observed after 9 months of this therapy. We contemplated surgical excision of the lesion since the response to antifungals was very slow [Figure 4].

Figure 4

Post-treatment picture showing mild regression of the lesion