A Case of Phaeohyphomycosis Caused by Exophiala oligosperma in a Renal Transplant Patient Successfully Treated with Posaconazole

Corresponding Author: Asaph C Levy Hofstra North Shore-LIJ School of Medicine, North Shore University Hospital, North Shore-LIJ Health System Manhasset, NY, United States Email: asaphlevy@gmail.com Abstract: Phaeohyphomycosis is an uncommon mycotic infection caused by dematiaceous fungi. We report a 53-year-old male who presented with phaeohyphomycosis on his upper extremities, 6 months after renal transplantation. Biopsy revealed pigmented moniliform hyphae and cultures grew Exophiala oligosperma. The lesions completely resolved after 3 months of treatment with posaconazole.


Introduction
Phaeohyphomycosis is an uncommon infection that is caused by an increasing number of dematiaceous, or pigmented fungi. Infections caused by these pigmented moulds are thought to be opportunistic fungal diseases. The pigment is due to the presence of melanin in their cell walls. Infections can either be localized to subcutaneous tissue, or they can progress to disseminated disease, which can affect solid organs, such as the lungs, as well as the CNS (Murray et al., 2012). Post-transplant mycoses are mostly comprised of mycelial organisms (Schieffelin et al., 2014). There are a large number of these dark genera that cause human infection, however, the most common include: Alternaria, Bipolaris, Cladosporium, Curvularia, Exophiala and Exserohilum species (Murray et al., 2012). Phaeohyphomycosis typically presents as a localized subcutaneous or deep-seated infection; commonly as a cyst or abscess (Pai et al., 2013).
These opportunistic fungal infections are becoming progressively more relevant to post-transplant patients. Fungal infections caused by filamentous fungi make up a large proportion of fungal infections and non-Aspergillus species, including those genera inciting phaeohyphomycosis, make up 27% of invasive mycelial fungal infections (Schieffelin et al., 2014). It is thought that as the number of solid organ transplant recipients continues to increase, as will the incidence of phaeohyphomycosis in these immunocompromised patients (Schieffelin et al., 2014).

Case Report
A 53-year-old retired male with a past medical history of adult polycystic kidney disease, status post kidney transplant 7 years prior and a deceased donor kidney transplant 6 months prior, was incidentally found to have erythematous, non-pruritic, papular lesions on his upper extremities bilaterally, during an admission for Superior Vena Cava (SVC) syndrome ( Fig. 1, Supplementary Data). He did not recall any trauma to his arms. He received thymoglobulin and hydrocortisone for induction and was continued on tacrolimus and mycophenolate for his recent transplant. He was then transitioned to cyclosporine and ultimately to belatacept and prednisone for maintenance therapy. His vital signs were stable and he remained afebrile throughout the admission. Upon examination, he was found to have erythematous slightly tender nodules, some with central vesicles, on bilateral upper extremities. No regional lymphadenopathy was appreciated. Routine labs including complete blood count, basic metabolic panel and hepatic function tests were within normal limits, in the context of his recent transplant. However, due to the patient's immunocompromised state, these lesions raised clinical suspicion for possible infection and dermatology was consulted. A punch biopsy and tissue culture were performed. Histopathology revealed a suppurative granuloma in the dermis containing slightly pigmented moniliform fungal hyphae ( Fig. 2 and 3, Supplementary Data). Periodic acid-Schiff (PAS) and Grocott's Methenamine Silver (GMS) staining were positive, confirming fungal infection (Fig. 4, Supplementary Data). Acid Fast Bacilli (AFB) stain was performed, which was negative for mycobacteria. Initial tissue cultures were positive for few mold-like fungi and gram stains were negative.
The presumptive diagnosis of phaeohyphomycosis was made at this time. Further identification of the isolate and antifungal susceptibility testing were performed at the Fungus Testing Laboratory at the University of Texas Health Science Center at San Antonio (UTHSCSA), which revealed Exophiala oligosperma as the causative pathogen. MRI of the brain and CT scan of the sinuses and chest were all subsequently ordered to evaluate for disseminated infection. All imaging and blood cultures were negative and the diagnosis of subcutaneous phaeohyphomycosis was confirmed. The patient was then started on a course of posaconazole. His posaconazole level was maintained in therapeutic range throughout the admission and he remained compliant upon discharge. The lesions appeared to improve after 10 days of treatment, with marked improvement after 2 months of therapy. The lesions have completely resolved after 3 months of treatment.

Mycology
The isolate was accessioned into the Fungus Testing Laboratory collection as UTHSCSA DI15-4. Colonies on Potato Flakes Agar (PFA) prepared in-house were olivaceous to black and initially mucoid, becoming velvety after 12 days of incubation at 25°C (Fig. 5A, Supplementary Data). Microscopic observations on a PFA slide culture under the same conditions revealed both annellated yeast cells and conidia. Annelloconidia were produced from relatively short, inflated conidiogenous cells, as well as from intercalary loci. (Fig. 5B-C, Supplementary Data). For molecular identification, a portion of the cultured isolate was suspended in Buffer G2 (Qiagen, Valencia, CA) followed by lysing in a bead beater instrument (BioSpec Products, Inc., Barlesville, OK). Proteinase K was added and the samples were incubated at 56°C for one hour. After incubation, the DNA was extracted using the EZ1 DNA tissue kit on the BioRobot EZ1 instrument (Qiagen) according to the manufacturers instructions. Extracted DNA was used for PCR amplification of ITS and D1/D2 regions as described (Romanelli et al., 2010). PCR products were then sequenced using the ITS1 and ITS4 primers as well as NL1 and NL4 primers at the UTHSCSA Molecular Diagnostics Laboratory (White et al., 1990). Sequences were assembled and analyzed using DNASTAR SeqMan Pro version 9.1 (DNASTAR, Inc., Madison, WI) and queried in GenBank using the BLASTn algorithm available on the NCBI site (www.ncbi.nlm.nih.gov) and were also compared to those available in the CBS-KNAW Fungal Biodiversity Centre database (www.cbs.knaw.nl). The ITS sequence showed 100% identity to both E. oligosperma (GenBank Accession No. AB480204.1) and E. jeanselmei (GenBank Accession No. AJ866273.1), while the D1/D2 sequence showed 100% identity with E. jeanselmei (GenBank Accession No. KC311520.1). By barcode analysis, there was 100% match with E. oligosperma (UTHSC 91-870) (Heinrichs et al., 2012). Based on the above, the isolate was identified as E. oligosperma. The ITS and D1/D2 nucleotide sequences have been deposited into GenBank under accession numbers KP938216 and KP938217, respectively. Antifungal susceptibility testing was performed according to the methods described in the Clinical and Laboratory Standards Instituted (CLSI) M38-A2 document for filamentous fungi (CLSI, 2008). The Minimum Inhibitory Concentration (MIC) for amphotericin B was 2 µg Ml −1 , 8 µg Ml −1 for fluconazole and 0.25 µg Ml −1 each for posaconazole and voriconazole. Hoog et al. (2003) by sequencing of its ribosomal DNA. Exophiala species are environmental fungi that are associated with decaying wood and soil organic wastes. E. jeanselmei is the most frequently cited of the Exophiala species as a human pathogen, however sequence data has subsequently shown that E. jeanselmei is a species complex and that many of these case reports would represent other species if characterized at the molecular level. The most common clinically relevant species in the United States is E. dermatitidis (Zeng et al., 2007). Other species such as E. moniliae, E. oligosperma and E. spinifera have been implicated as well (Zeng et al., 2007). Clinical manifestations for this species include mycetoma, localized cutaneous infections, subcutaneous cysts, endocarditis, and cerebral and disseminated infections (UA, 2001). The cutaneous manifestations are nonspecific, therefore it is important to have a high index of suspicion for fungal infection in order for early diagnosis.

E. oligosperma was first described in 2003 by De
Phaeohyphomycosis is most commonly diagnosed in immunocompromised patients, however, there have been reported cases of infection in immunocompetent patients; including a case reported by Venkateshwar et al. (2014). Over past 12 years there have been a handful of infections with E. oligosperma, including a case reported by Rimawi et al. (2013) that describes a patient with a 10-year history of lupus and history of severe asthma, taking mycophenolate and methylprednisolone, who was successfully treated for E. oligosperma infection with a 3 month course of voriconazole (Rimawi et al., 2013). The included literature review noted 6 other reported cases of E. oligosperma infection that were susceptible to voriconazole and included 1 renal transplant patient reported by Gonzalez-Lopez et al (2007). This renal transplant patient presented with phaeohyphomycosis 7 years after transplantation and was successfully treated with a 3-month course of itraconazole; with full resolution (Gonzalez-Lopez et al., 2007). The Gonzalez-Lopez et al. (2007) case is similar to ours, as the patient was immunosuppressed with mycophenolate, prednisone, and tacrolimus. However, our patient presented within 6 months of transplantation. Our patient received higher doses of immunosuppressive therapy; which may have been a contributing factor to his earlier development of phaeohyphomycosis in the postoperative period. A summary of previously reported skin infections with E. oligosperma is shown (Table 1) (Bossler et al., 2003;Tokuhisa et al., 2011;Kan et al., 2013;Sato and Yaguchi, 2013;Fukai et al., 2013).
Optimum treatment has been thought to be surgical excision and anti-fungal therapy; although there have been reports suggesting local hyperthermia as an effective treatment as well (Fukai et al., 2013). Surgical excision is typically reserved for those patients who have solitary lesions. As our patient had multiple nodules, we decided systemic anti-fungal therapy was the best option for treatment. Voriconazole and itraconazole have had the best record for treatment; however, we demonstrate that posaconazole is effective as well. Although susceptibility was ordered, we did not obtain it before starting him on posaconazole. Since he had a favorable response to the therapy, he was continued on a 3-month course. If there had been evidence of disseminated infection, the plan was for combination therapy with both posaconazole and amphoteracin B. To our knowledge, this is the first case of subcutaneous E. oligosperma infection that has been successfully treated with posaconazole.