Rare Cutaneous Fungal Infection Due to Nigrograna chromolaenae in a Heart Transplant Recipient

Abstract

Introduction: Solid organ transplant recipients are particularly prone to infections, and many germs can be involved, including opportunistic pathogens. Regarding catheter-related infections however, the number of causative microorganisms is most often limited to germs of the skin flora, rare enterobacteria and Pseudomonas aeruginosa. Case report: We present here a case of venous catheter-related cutaneous infection in a man with immunosuppression, which was surprisingly caused by a rare environmental fungus, named Nigrograna chromolaenae. The therapeutic strategy combining posaconazole and removal surgery appears to have been effective, with no relapse more than 2 months after surgery. Conclusions: Due to advances in molecular biology techniques, it is possible that infections with Nigrograna spp. will be increasingly described. At the moment the reported cases are few in number, and the treatment is not yet standardized, which is why we thought this new case could support the literature about these opportunistic pathogens.

Introduction

Solid organ transplant recipients are particularly vulnerable to infections, especially in the first year following the transplant, and the number of microorganisms potentially involved in these patients, including opportunistic pathogens, is significant. Regarding nosocomial infections however, especially those related to venous catheters, the number of causative microorganisms is most often limited to germs of the skin flora (including Candida spp. among the fungi), rare enterobacteria and Pseudomonas aeruginosa.

We describe here the case of a heart transplant recipient who developed a catheterrelated cutaneous infection that did not respond to antibiotic treatment, which surprisingly turned out to be due to a rare environmental fungus (Nigrograna chromolaenae). These fungi have already been described as causing rare human diseases [1,2], but the nosocomial nature of this infection particularly caught our attention.

Case Report

A 46-year-old patient underwent an orthotopic heart transplant in June 2024 in the context of a severe genetic heart disease. His medical history was also notable for type 2 diabetes, hyperthyroidism and chronic renal insufficiency. Six weeks after the transplant he was hospitalized for 8 days for severe acute diarrhea, and his condition required intravenous medication. We first met the patient in October of the same year, during a hospitalization for right heart failure, because he complained of an ulcerated cutaneous lesion on the left forearm. He explained that the wound had appeared about a month earlier at a former peripheral venous catheter site, shortly before his discharge from hospital, and despite daily dressings it had gradually worsened over a few weeks (Figure 1). At that time his immunosuppressive regimen included tacrolimus (1.5 mg twice daily), prednisone (20 mg daily) and mycophenolate mofetil (500 mg twice daily).

Clinical examination revealed a unique purplish papule on the forearm of about 10 cm in long axis, with inflammatory edges and a crusty and ulcerated center. There was no associated pain or itching sensation, and the patient had no memory of a recent splinter wound to his hand or a scratch. The remainder of the physical examination was normal, including careful examination of the entire body surface and oral mucosa. Skin biopsies were performed and the first tissue cultures yielded numerous Escherichia coli and Staphylococcus aureus which was suggestive of ecthyma gangrenosum. The patient therefore completed a 7-day course of IV ceftriaxone but without improvement.

Shortly afterwards histological analysis of skin biopsies was suggestive of a fungal disease, explaining the failure of ceftriaxone. In periodicacid-Schiff and Grocott staining numerous structures of varying size were observed. Some elements were round, others filamentous, and some were pigmented. The epidermis was hyperplastic, with polymorphonuclear abscesses, and an abundant interstitial inflammatory infiltrate was seen in the dermis.

Finally, prolonged culture from the biopsies yielded pigmented filamentous colonies on Sabouraud dextrose agar plate (BioMérieux, France) after 10 days at 25°C. From above, the colonies were grey, fluffy with a central bulge and dark pigmented in reverse. Microscopic analysis performed on culture after 15 days (lactophenolcotton blue staining) were not contributive as they showed filaments without fructification (Figure 2). Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-ToF MS) (Bruker MicroFlex Biotyper, Germany) was performed on the colonies after a complete extraction protocol, carried out according to the manufacturer's instructions. Spectrum analysis was performed using successively MBT Filamentous Fungi Library and MSI V2.0 databases but remained unsuccessful. The fungal isolate was therefore sent to the National Reference Center in Pasteur Institute (Paris, France) for accurate identification using polymerase chain reaction then gene sequencing, and a strain of Nigrograna chromolaenae was identified. Unfortunately, no antifungal susceptibility testing could be performed because of the absence of fructification of the fungus. Furthermore, cultures for mycobacteria remained sterile.

The patient being immunosuppressed we then looked for signs of disseminated disease. An arm MRI did not show any deep abscesses, but dermohypodermitis of the forearm which extended beyond the superficial aponeurosis. The brain MRI revealed no abnormalities. The (18)F-FDG-PET/CT showed four subcutaneous calcified nodules of 1.5 mm in diameter on the thighs, and a few small nonspecific pulmonary nodules. The patient did not complain of fever or cough and the pulmonary nodules were nonspecific, which is why no bronchoscopy was scheduled. Furthermore, the subcutaneous nodules on the thighs were attributed to repeated insulin injections, and we finally concluded that the infection was localized.

Given the rarity of Nigrograna infection, we based the strategy both on the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) guidelines and on advice of experts from the National Reference Center in Pasteur Institute, and the patient ultimately received both oral antifungal therapy and excisional surgery [3]. Since the size of the lesion was significant (10 cm long), we first tried to reduce it with oral posaconazole treatment (loading dose, then 300 mg once daily, then 200 mg once daily, according to the serum trough concentrations). We hoped that this would allow for less damaging surgery. Furthermore, to increase the chances of recovery, reducing immunosuppressive treatment was suggested at this stage, but this was ultimately impossible since the heart transplant was less than a year old. Therapeutic monitoring of tacrolimus was regularly performed, due to expected drug interactions with azole, and the levels always remained within the targets. After a month of posaconazole the dimensions of the lesion had already been halved and the wound was no longer ulcerated (Figure 3).

This effective and well tolerated treatment was therefore continued while waiting for surgery, which could be performed after 10 weeks. The skin excision measured 5 x 3 cm (including 1 cm of healthy margins), and skin closure was achieved by an artificial dermis graft. Of note, intraoperative samples found no concurrent infection, including prolonged fungal cultures. Posaconazole was continued for another month after surgery, for a total duration of 3.5 months to reduce the risk of local recurrence, and until now no relapse was observed with a follow-up of just over 2 months.

Discussion

The genus Nigrograna belongs to the Pleosporales and includes fungi that are responsible for phaeohyphomycosis. Phaeohyphomycosis are rare diseases characterized by the synthesis of melanin by the fungus, which gives a black appearance to the hyphae. However, several characteristics distinguish them from other dematiaceous fungi causing chromoblastomycosis. There are many species, among which Alternaria spp. and Exophiala spp. are the best known.

The genus Nigrograna was first described in 2012 [4], and for several years Nigrograna and Biatriospora, which are phylogenetically close, were considered as one and the same genus, but a little less than 10 years ago some authors have proven that they are actually genetically distinct [5,6]. Nigrograna spp. are environmental dematiaceous fungi mainly isolated from plants and distributed on at least 4 continents [5,7]. More recently it has also been shown that some species thrive in a marine or freshwater environment. More than 40 species have been identified to date, and most are saprotrophs or endophytes on various types of hosts [5,7].

Since the accurate identification of Nigrograna spp. necessarily requires molecularbased methods, it is likely that the prevalence of these infections is currently underestimated. In addition, the terms Nigrograna and Biatriospora have been used as synonyms for several years, which may also bias the count of cases. Today, it appears that human infections with Nigrograna spp. are relatively uncommon, but Nigrograna mackinnonii, which is the best-known pathogenic species, is still recognized as an agent of black grain eumycetoma in humans [5,8].

Not counting fungal eumycetomas, very rare cases of cutaneous phaeohyphomycosis due to Nigrograna spp. have recently been described: for example, Puing et al. [1] isolated Nigrograna mackinnonii in a kidney transplant recipient, and Wang et al. [2] diagnosed infection due to Nigrograna hydei in a rather elderly but otherwise immunocompetent woman. In each case the main hypothesis was that of an inoculation disease, but without the patient remembering the initial injury.

Considering previously published articles, we found this case report relevant for two main reasons. Firstly, Nigrograna infections are little known, and to our knowledge Nigrograna chromolaenae has not yet been described as pathogenic for human beings. Secondly, since Nigrograna spp. are most often associated with plants and wood, it is surprising that this germ was isolated from a catheter-related infection. Furthermore, our patient did not usually garden and had not handled plants during the previous weeks, which did not make us suspect a telluric or environmental microorganism. He only remembered that during his last hospital stay his catheter, located on the front of his forearm, could have been contaminated by food or freezedried coffee during meals. Catheters are normally covered with a transparent, adhesive, semiocclusive film, and inoculation with this fungus is not well explained at this stage. This case clearly demonstrates that infections with Nigrograna spp. can occur in a wide variety of circumstances, which are not always easy to suspect.

The rarity of the infections due to Nigrograna spp. explains why the optimal management is not yet well standardized and the therapeutic strategies are varied: topical antifungal treatment, oral antifungal therapy, resection surgery or combination of treatments have already been used [3,9]. Some teams choose the management strategy according to the degree of immunosuppression, reserving the medicalsurgical strategy for immunocompromised patients. Here we have followed both the ESCMID guidelines and advice of experts from the National Reference Center in Pasteur Institute [3]. Antifungal susceptibility testing was unsuccessful because the fungus didn’t develop fructifications, so, we were advised to prescribe posaconazole as empirical therapy, which showed fairly good efficacy and tolerance. Posaconazole is a newer antifungal than itraconazole, which may explain why it was not mentioned first in the ESCMID guidelines, published in 2014, due to a lack of sufficient experience at that time in the treatment of these fungal diseases [1]. However, posaconazole is nevertheless an alternative proposed by Chowdhary et al. and according to several authors, some patients suffering from infections by dematiaceous fungi have been cured under Posaconazole [1,3,9,10]. Furthermore, in the context of empirical treatment as was the case here initially, this molecule seemed interesting: a broader spectrum than itraconazole, fewer side effects than with voriconazole, and fewer drug interactions than with other azoles (especially with immunosuppressive drugs). We chose to stop treatment one month after surgery, for a total of 3.5 months of treatment. This duration seemed appropriate for this ultimately localized infection, and because the excision could be performed with healthy margins which limited the risk of recurrence. However, the ESCMID guidelines do not specify the duration of treatment required for these infections, and in some cases no antifungal had been prescribed [3]. The second case presented by Lo Porto et al. is also rather reassuring regarding this duration of treatment: 3 months of itraconazole were effective in addition to surgery, despite a first relapse, and in the review he conducted, the median duration of treatment for phaeohyphomycosis was 16 weeks [9]. Given this uncertainty, prolonged monitoring will obviously be proposed to our patient.

In the management of phaeohyphomycosis surgery is not always mandatory [3,9]. However, we proposed here complete surgical removal, despite the clear improvement under posaconazole, in order to reduce the risk of recurrence in the context of intense immunosuppression [3]. Indeed, since the heart transplant was recent the immunosuppressive treatment could not be reduced despite this infection. Today, after more than 2 months of follow-up, healing is continuing well, with no signs of relapse.

Conclusions

We wanted to emphasize here that in very immunocompromised patients, a nosocomial infection as common as a venous catheter infection can sometimes be due to a very rare pathogen that does not belong to the skin flora.

Given the more frequent use of molecular methods (crucial for this diagnosis) and the constant rise in the number of immunocompromised patients, the incidence of infections with Nigrograna spp. may increase in the coming years. It therefore seems important to us that diagnosed cases are reported, to facilitate the updating of guidelines for the management of phaeohyphomycosis, and thus optimize the care of the most fragile patients.