Post‐traumatic Pseudallescheria apiosperma osteomyelitis: positive outcome of a young immunocompetent male patient due to surgical intervention and voriconazole therapy

Abstract

Pseudallescheria species, with their anamorphs classified in Scedosporium1 are worldwide distributed fungi with a predilection for nutritionally rich, polluted soil and water.2–4Scedosporium and Pseudallescheria species are also emerging human-pathogens causing local infections in immunocompetent individuals5–8 and disseminated infections in immunocompromised individuals.9,10 Deep infections due to Pseudallescheria species are rarely found in humans without underlying disorders,8 but due to recently developed identification tools they are increasingly diagnosed11–13 e.g. in patient populations with chronic pulmonary disorders. Pseudallescheria species cause systemic infections which are difficult to treat due to the therapy-refractory nature of these aetiological agents14. Successful cure of local, subcutaneous infections may be achieved only by a combination of surgery and antifungal therapy.15 The present case describes the successful treatment of an immunocompetent young male patient suffering from a severe, post-traumatic Pseudallescheria apiosperma osteomyelitis of the tibia. Cure of the patient was achieved by long-term voriconazole administration and surgical debridement of infected soft tissue and bone. A previously healthy and otherwise immunocompetent 16-year-old male patient suffered from an open, post-traumatic tibia-fracture on the left lower limb. In May 2006, the patient had a motorcycle accident; besides the tibia fracture there were no deep traumatic injuries. Since the wound was contaminated with soil and dirt particles, an antibiotic regimen was started preoperatively on an empirical basis with 3 dd of 1.1 g amoxicillin/clavulanic acid intravenous (i.v.) plus 3 dd of 500 mg i.v. metronidazole. As the wound did not respond to broad-spectrum antibiotic therapy, the antibiotic regimen was changed to targeted therapy against Enterococci sp. with ampicillin/sulbactam and clindamycin combined with fosfomycin for coverage of staphylococci (all dosages were body-weight adjusted). During the first surgical intervention an intramedullary nail was implanted into the tibia to stabilise the left lower leg (Fig. 1e). Despite early antibiotic therapy, the patient developed a deep soft tissue infection resulting in a muscle defect on the surgical wound site. Soft tissue infection was initially supposed to being caused by multi-bacterial infection. His muscle defect was reconstructed by plastic and reconstructive surgery transplanting a flap of the patient’s musculus gracilis. After autologous muscle transplantation, a soft tissue healing defect and persisting fistula were noted. (a) Pure culture colonies of Pseudallescheria apiosperma, grown for 72 h on Sabouraud 2% agar; gained from an intraoperative swab. (b) Pseudallescheria apiosperma microscopical characteristics in 400-fold magnification stained with lactophenol aniline blue. (c) Intraoperative site with pseudarthrosis of left tibia. (d) Removed infected bone fragments of the left tibia, the two largest bone pieces measured 9.0 cm in length and up to 2.0 cm in width. In addition, some smaller bone fragments were removed, which were in size up to 3.0 cm in length and up to 2.0 cm in width. (e) The X-ray image of the originally implanted intramedullary placed tibia nail. (f) The X-ray image of the lower left leg demonstrating the successful implanted autologous bone-interponate. First postoperative microbiological cultures from the infection site (3 weeks postoperatively) yielded no microbial growth after 72 h. Seven weeks postoperatively, while wound secretion and other local signs of infection increased, deep tissue cultures yielded Enterococcus faecalis and Clostridium clostridioforme. Samples were negative for fungi after a total incubation time of 72 h at 37 °C on Sabouraud 2% glucose agar (standard routine medium). Systemic clinical and laboratory signs for infection remained low (CRP 2 mg l−1, leucocytes 5000 μg ml−1). Whole body granulocyte-scintigraphy exclusively revealed high activity in the left proximal and distal tibia regions. Eleven weeks post operation, an intraoperative swab (revision surgery) was found to be positive for Pseudallescheria/Scedosporium and E. faecalis. Intravenous ampicillin administration (2 weeks 3 dd of 1.0 g) combined with voriconazole (2 weeks 2 dd of 400 mg; then 2 dd 200 mg) was started immediately. The Pseudallescheria/Scedosporium-infection persisted; the fungus was re-isolated from the fistula under voriconazole treatment. The patient developed a pseudarthrosis (Fig. 1c) at the fracture site and was treated with a bone auto transplantation and external fixation (1, 2). During surgical exploration the infected, non-vascularised bone was removed. The two largest pieces of infected bone were 9.0 cm in length and up to 2.0 cm in width (Fig. 1c,d). In addition, smaller bone fragments and infected soft tissue were removed (Fig. 1d). After surgical debridement of infected material and auto transplantation, oral voriconazole treatment (2 dd of 200 mg) was continued for 6 months. Voriconazole had no severe side effects except body weight reduction after 5 months of therapy from 53 kg to 48 kg. During the first 3 weeks, the patient complained about tiredness, dizziness and exhaustion. Patient’s lower left limb after bone auto transplantation. The patient was followed up closely by repeatedly sampling the fistula, but no growth of fungi or bacteria was observed. One year after auto transplantation, scintigraphy and X-ray were performed, and no signs of inflammation at the fracture site were found and the patient remained without pathological findings. Four years after therapy (2010) a stable left lower leg with normal length was observed, which remained symptomless also under conditions of physical stress and without relapse of fungal growth, indicating the successful resolution of the Pseudallescheria/Scedosporium infection. Identification down to generic level (Pseudallescheria/Scedosporium) was performed using morphological characteristics in the routine laboratory (Fig. 1a,b). As for specific identification according to the latest taxonomy1,16–18 molecular analysis is necessary, the strain was forwarded to the CBS-KNAW Fungal Biodiversity Centre (Utrecht, the Netherlands), where the strain was identified as Pseudallescheria apiosperma. The isolate was deposited in the CBS reference collection with accession number CBS 120510 and the ITS sequence was submitted to GenBank as JF309076. Antifungal susceptibility was tested using Etest® (bioMérieux, Vienna, Austria) for voriconazole (VCZ), posaconazole (PCZ) and caspofungin (CAS) according to the manufacturer’s specifications. Minimal inhibitory concentration (MIC) of VCZ was 0.19 mg l−1, of PCZ 1.5 mg l−1 and of CAS 32 mg l−1. Two additional Scedosporium strains were re-isolated from the infected site, when patient was ten days and three weeks under VCZ therapy, respectively. Osteomyelitis by Pseudallescheria/Scedosporium is characterised by slow progression, often with a delay of months between probable inoculation, first symptoms and final isolation of the fungus from clinical samples.8,19 The most frequently affected sites are the lower limbs, especially the knee joints leading to arthritis.6,8,20,21 The infection nearly exclusively results from trauma involving foreign bodies or soil.6,19,21 The habitat of the aetiological agents is contaminated soil particles or street oil and refuse and therefore Pseudallescheria/Scedosporium infection pose an extra risk factor for patients suffering from traffic accidents and other major traumata.22 Due to its slow progression the fungus is isolated from deep tissue samples only in a late stage of infection. In routine diagnostics the infection may be overlooked by using exclusively full media. Maybe the usage of a semi-selective media, such as, SceSel+ would have resulted in an early Scedosporium-positive culture technical proof.23 In our case the microbiological laboratory incubated the samples for 72 h, which is not enough to recover most filamentous fungi other than Aspergillus, and hence the result was evaluated as negative. Only due to the absence of clinical improvement and multiple antibiotic therapy failures, repeated attempts finally yielded Pseudallescheria/Scedosporium. Other authors recommended incubating culture plates for at least 14 days.22,24 Apparently the fungus needs a sufficient biomass in tissue for successful germination on culture media. The Pseudallescheria/Scedosporium complex has recently been subdivided into a number of taxa, which seem to differ in virulence,3 but statistical data of case studies are needed to corroborate this hypothesis. Pseudallescheria apiosperma and P. boydii represent the most common species involved in human infections.25 Stipeli et al. [8] described a post-traumatic infection by P. apiospermum in a 10-year-old immunocompetent girl. She was cured with long-term intravenous voriconazole administration. Kooijman et al. [6] reported osteomyelitis due to Scedosporium aurantiacum in an immunocompetent man after major trauma. The patient developed a fistula and an osteomyelitis under antibiotic treatment. Also this patient was cured by surgical debridement, wound cleaning and long-term voriconazole therapy. Most Pseudallescheria/Scedosporium species other than S. prolificans are susceptible to VCZ and case studies report good patient outcomes.26 Using Etest® our strain had in vitro low MICs (MIC 0.19 mg l−1 and 0.25 mg l−1) and therefore VCZ was used to treat the patient. There was no evidence for substantial resistance development under voriconazole since MIC values of Scedosporium strains remained stable during ongoing voriconazole therapy. Since patient was not responding to therapy, non-vascularised and severely inflamed, infected bone and surrounding soft tissue were removed followed by bone auto transplantation. Even though VCZ is well distributed to all body sites27 and the causative strain had very low MICs for this compound, therapeutic concentrations of VCZ may not be reached in non-vascularised infected bone areas. In such cases, surgical excision combined with local and/or systemic antifungal therapy is mandatory.6 The penetration of voriconazole into infected sites may be limited by poor blood circulation and by the size of infected area (Fig. 1d). In this case, after removal of infected tissue patient responded to voriconazole therapy and showed rapid clinical improvement. To avoid a relapse, voriconazole therapy was continued postoperatively for six months. The teenaged male patient, pre-accidentally without clinical history, tolerated voriconazole well, except for loss of body weight and minor side effects (tiredness, dizziness and physical exhaustiveness) during the first three weeks of therapy. Since voriconazole is available as oral and intravenous formulation, oral long-term therapy on an out-patient basis was possible. The patient experienced no side-effects during several monitoring examinations. After four years of follow-up, the patient had a leg of normal length with no evidence of disease relapse. We thank the support extended by the local infection control team of the Unfallkrankenhaus Salzburg (Ms Bettina Penninger and Dr Bodo Kirchner) and the medical director of the Unfallkrankenhaus, Dr Alois Karlbauer. The author have no conflict of interests to declare.