Locally extensive angio-invasive Scedosporium prolificans infection following resection for squamous cell lung carcinoma

Abstract

We report a case of Scedosporium prolificans infection in a patient following surgery for squamous cell lung carcinoma. Combination therapy with voriconazole and terbinafine was commenced for intrathoracic infection and mycotic vasculitis. In spite of antifungal treatment, he developed culture-positive sternal and rib osteomyelitis four months later. Scedosporiosis is not commonly reported in patients with solid organ malignancies, and this case highlights its aggressive nature and propensity for direct local invasion.

1. Introduction

Scedosporium prolificans is a ubiquitous dematiaceous filamentous fungus. Clinical disease can range from asymptomatic colonisation of the respiratory tract, invasive infection involving adjacent and deep structures, and disseminated infection involving distant sites. In the immunocompetent host, infection can also result from penetration of spores due to direct trauma or surgery. S. prolificans is an emerging pathogen in immunocompromised hosts, particularly those with prolonged neutropenia. It is highly resistant to antifungals from multiple classes, although synergy has been demonstrated with various combinations of antifungal agents. Here we report a case of locally invasive and aggressive S. prolificans in a non-neutropenic patient where S. prolificans was still able to be cultured after four months of combination antifungal therapy and whose treatment course was complicated by highly variable plasma voriconazole levels.

2. Case

A 44-year old man was admitted to our institution for resection of a right-sided apical squamous cell carcinoma of the lung (T4N0M0). He had been diagnosed 3 months earlier in the context of non-resolving right apical chest radiographic changes, haemoptysis, Horner's syndrome and right arm motor weakness. Imaging confirmed an apical Pancoast tumour with local invasion of the subclavian vessels and brachial plexus. He underwent local irradiation and chemotherapy (cisplatin, etoposide) two months prior to arrival at our hospital. Due to extensive local invasion he was referred for specialist thoracic, vascular and neurosurgical intervention for tumour resection. His other relevant medical history was malignancy-associated bilateral pulmonary emboli and deep venous thrombosis treated with enoxaparin and inferior vena cava (IVC) filter.

Surgical resection (day 0) was prolonged and technically difficult due to tumour infiltration of surrounding perineural and vascular structures, however histology of the resected tissue revealed post-radiotherapy changes with no residual neoplasia. Surgical margins and surrounding lymph nodes were also negative for malignancy. The immediate post-operative period was unremarkable and he was discharged home on day +9. He returned on day +16 with pleuritic chest pain, dyspnoea and fever. Computed tomography (CT) of his chest revealed a large loculated complex collection containing solid and fluid components in his right thoracic cavity (Fig. 1A). The collection extended into the mediastinum and retrosternal region adjacent to his sternotomy wires, and caused mediastinal shift to the left. He underwent video-assisted thorascopic surgical (VATS) drainage of the collection on day +17. Postoperatively (day +19) he survived three episodes of cardiac arrest requiring cardiopulmonary resuscitation, exploratory right- and left-sided thoracotomies and internal cardiac massage. Massive bleeding from the right subclavian artery was noted and required ligation. Decortication of the right middle and lower lobes was also performed. Twelve days later (day +31) he developed incipient pericardial tamponade and required a left anterolateral thoracotomy for pericardial fluid drainage and pericardial window formation. Other post-operative complications included atrial tachy-arrhythmias managed with sotalol, difficult pain control, depression and physical deconditioning.

Fig. 1.

Radiographic images of chest and brain. (A) Computed tomography of chest (day +16) demonstrating a massive collection within the right hemithorax comprising solid and fluid components and multiple gas locules. There is extension to the retrosternal region without bony erosion or destruction. (B) Computed tomography of chest (day +108) demonstrating 8 mm pulmonary nodule in left lower lobe and resolution of previous right hemithorax changes. (C) Magnetic resonance imaging of brain (day +284), T2-weighted signal, demonstrating right frontotemporal lobe ring-enhancing lesion with some surrounding oedema at the grey-white matter interface.

Pleural fluid and tissue obtained from the VATS procedure contained moderate numbers of neutrophil polymorphs and cultured S. prolificans with no other bacterial pathogens. Antifungal susceptibility testing demonstrated in vitro resistance to posaconazole (minimum inhibitory concentration [MIC]>8 mg/L), voriconazole (MIC>8 mg/L), amphotericin B (MIC>8 mg/L) and flucytosine (MIC>64 mg/L). Synergy testing was not performed on this isolate. Histology of the subclavian artery revealed an acute necrotising vasculitis associated with proliferation of fungal spores and septate hyphae at the adventitial aspect of the blood vessel consistent with mycotic vasculitis (Fig. 2A–C). Unfortunately this tissue was not submitted for microscopy and culture. Pericardial fluid revealed mild active chronic pericarditis but was culture negative for bacteria, mycobacteria and fungi. He was commenced on intravenous (IV) voriconazole (6 mg/kg loading dose for 48 h then 4 mg/kg twice-daily) and oral terbinafine 250 mg twice daily. Electrocardiographic monitoring was mandated by the combined use of voriconazole and sotalol but did not reveal any QT interval prolongation. Routine CT scanning of his brain and sinuses did not reveal any evidence of fungal disease. An immunodeficiency screen was unremarkable (human immunodeficiency virus serology, immunoglobulins, immunoglobulin G subclasses, serum protein electrophoresis), and he had normal white blood cell and neutrophil counts with a mild lymphopenia (0.8×10⁹/L; reference 1–4×10⁹/L). The absolute CD4 count was low (262 cells/μL; reference 330–1310 cells/μL) but was consistent with his lymphopenia, and CD4 percentage was normal (36.2%; reference 35–59%). A repeat CD4 count was not performed. Further history was obtained from the patient, and he reported spending time in a newly created vegetable garden following diagnosis of his lung carcinoma.

Fig. 2.

Histology of right subclavian artery. (A) Haematoxylin and eosin stain, 4x magnification. The subclavian artery shows an acute necrotising vasculitis, with extensive necrosis of the vessel wall in association with an invasive fungal proliferation at the adventitial aspect of the vessel. Arrow: vascular mural necrosis and inflammation. (B) Periodic acid-Schiff (PAS) stain, 10x magnification. PAS stain highlights the fungal micro-organisms invading the wall of the artery. Arrow: fungal elements within adventitia. (C) PAS stain, 40x magnification. Fungal elements consist of sports and septate hyphae.

Voriconazole therapy was complicated by variability in plasma levels. Initial steady state trough levels were supratherapeutic (12.8 mg/L) and were associated with visual hallucinations; the subsequent maintenance dose of oral voriconazole was 250 mg twice daily in combination with terbinafine. Despite these initial problems with voriconazole toxicity, maintaining plasma voriconazole trough levels within the target range (1–5.5 mg/L) was subsequently difficult after two months of therapy (Table 1). None of his concomitant medications are known to be associated with increased voriconazole metabolism, so autoinduction of hepatic metabolism was suspected. Apart from increasing voriconazole to 400 mg twice daily, pantoprazole 40 mg twice daily was also added for cytochrome P450 inhibition. He developed hepatic dysfunction, with elevated alkaline phosphatase (255 U/L; reference 35–110 U/L) and gamma glutamyltransferase (395 U/L; reference 5–50 U/L). Hepatic aminotransaminases and bilirubin were normal, and ultrasound and CT scanning of the abdomen did not reveal any anatomical hepatobiliary abnormalities or sub-diaphragmatic metastatic disease.

Table 1.

Variability in voriconazole plasma levels^a and dosing schedules.

Day	Voriconazole level (mg/L)	Voriconazole dose and comment
+21		Dose induction at 300 mg bd IV (4.3 mg/kg) Antifungal therapy commenced with presumptive diagnosis of Scedosporium spp. (four days after first VATS procedure)
+25	12.8	Patient reported visual hallucinations; dose altered to 300 mg bd PO on day +27
+35	6.3	Dose reduced to 250 mg bd PO on day +42
+59	<0.1
+79	<0.1	Assays confirmed with repeat testing at two different laboratories
+86	0.5	Dose increased to 300 mg bd PO on day +87
+93	1.2
+97	0.1
+100	0.47	Dose increased to 400 mg bd PO on day +114 (5.8 mg/kg)
+120	2.3
+148	1.4
+160	3.15
+181	0.9
+218	0.7	Dose increased to 500 mg bd PO on day +239 (8.1 mg/kg)
+246	3.5
+285	2.4
+293		Temporary cessation of voriconazole and terbinafine due to significant deterioration in liver function tests; restarted on day +304
+317	2.4
+340	0.5
+411	1.5	Cessation of antifungals due to nausea and vomiting, worsening liver function abnormalities and peripheral sensory neuropathy

^aA selection of plasma voriconazole levels are shown in relation to adjustments in dosing schedule.

Unfortunately there was dehiscence of the distal portion of his sternotomy wound associated with a methicillin-susceptible Staphylococcus aureus superficial wound infection requiring oral cephalexin and clindamycin. Inflammatory markers remained persistently elevated despite compliance with combination antifungal therapy, with C-reactive peptide (CRP)>150 mg/L (reference <5 mg/L). Repeat CT of his chest, abdomen and pelvis (day +108) demonstrated an 8 mm nodule in the apex of the left lower lobe of the lung felt to represent possible scarring, and there was no evidence of subdiaphragmatic metastatic or fungal disease (Fig. 1B). There was no evidence of sternal osteomyelitis or a retrosternal collection. He subsequently developed further sternal dehiscence involving the proximal midline wound, with extrusion of some sternal wires.

Four months after his original diagnosis with intrathoracic and angio-invasive S. prolificans infection (day +151 after tumour resection), he underwent debridement of his sternum with closure of the wound using a left pectoralis major muscle flap. Intra-operatively the sternum was noted to be necrotic; extensive debridement was undertaken and there were no associated fluid collections. In spite of receiving combination antifungals for four months, tissue obtained from the sternum and an adjacent rib grew S. prolificans. Susceptibility testing demonstrated in vitro synergy with the combination of voriconazole 0.5 mg/L and terbinafine 0.5 mg/L, (combined fractional inhibitory concentration 0.28 mg/L). No further surgical debridement was possible without causing loss of structural continuity of the sternum. Voriconazole plasma levels at this time were 1.5–3.5 mg/L, and combination antifungal therapy was scheduled to continue for 12 months after sternal debridement.

Over the next two months, voriconazole plasma levels became subtherapeutic again (<1 mg/L) despite no other medication changes and continuing pantoprazole. However the sternal wound and muscle flap remained healed and his inflammatory markers finally settled (CRP nadir 32 mg/L). Re-staging CT brain, chest, abdomen and pelvis were performed (day +108). The previously identified left lower lobe pulmonary nodule had now increased in size to 1.6 cm, and there was a new 5 mm enhancing subcortical lesion near the right temporal lobe. No mycotic aneurysms were noted on CT angiography of his neck and cerebral vessels. Due to concerns about possible cerebral fungal disease and known suboptimal plasma voriconazole levels, voriconazole was increased to 500 mg twice daily. This resulted in worsening cholestatic liver function abnormalities and the development of symptomatic peripheral sensory neuropathy and dysaesthesiae involving his feet.

Fine needle aspiration of the left pulmonary lesion was performed. Cytology smears contained macrophages; no fungal elements or malignant cells were seen. Fungal, mycobacterial and bacterial cultures were negative. Magnetic resonance imaging of his brain (day +284) revealed two ring-enhancing lesions in the right frontal lobe and left precentral gyrus (Fig. 1C). He underwent a stealth-guided left frontal craniotomy and excision of the left frontal lesion. Histology demonstrated moderately differentiated squamous cell carcinoma consistent with cerebral metastases from his original Pancoast tumour. There were no fungal elements identified, and there was no fungal, mycobacterial or bacterial growth on aspirate and tissue specimens.

After undertaking whole brain irradiation for cerebral metastases, he was subsequently diagnosed with progressive metastatic disease involving the liver, pancreas and axial skeleton. No residual fungal disease was detected in clinical specimens submitted for histopathology. In view of poor performance status, progressive paraesthesiae and dysaesthesiae, worsening nausea and abnormal liver function tests, voriconazole and terbinafine were stopped after completing 13 months of treatment (9 months following sternal debridement). Although he received successful treatment for S. prolificans infection, he received palliative supportive care for advanced metastatic cancer and died 12 months later.

3. Discussion

Scedosporium spp. are emerging and important pathogens in immunocompromised hosts [1–3]. Of note, break-through infections are occurring in neutropenic patients who are already receiving antifungal prophylaxis with mould-active agents [4]. Infection with S. prolificans is associated with increased mortality and invasive disease compared with S. apiospermum and S. auranticum [2,5], although recent animal models suggest S. auranticum may be as virulent as S. prolificans [6]. Sinopulmonary disease, bloodstream infection and cutaneous disease are the most common clinical features in the immunocompromised population [1,3,5,7,8]. It is highly resistant to most antifungal drugs with median MICs greater than 8 mg/L [2], however synergy has been demonstrated in vitro with the combination of azoles and terbinafine [9]. Several publications have reported clinical success with the combination of voriconazole and terbinafine [10–13].

Whilst extensive or disseminated disease has been reported in transplant recipients or patients with haematologic malignancies, our case is notable for widespread local disease including vascular invasion in the absence of ongoing immunosuppression. Cancer chemotherapy was reported as a risk factor for infection with S. prolificans in an Australian case series [5], although our patient had completed his chemotherapy more than 10 weeks prior to his first diagnosis of S. prolificans infection and had a normal peripheral white blood count. Although his CD4 count was low on a single measurement, the CD4 percentage of total lymphocytes was normal. In the absence of repeat testing it is uncertain whether CD4 lymphocytopenia was a potential contributing factor. In addition, only local structures around the thoracic cavity were infected (pleural cavity, right subclavian artery, sternum and first rib). We propose that prior exposure to S. prolificans through gardening activities led to colonisation of the respiratory tract in a patient with a smoking history and new lung neoplasm. Local spread was established following tumour invasion of local structures such as the right subclavian artery. Angio-invasive disease may have secondarily seeded to the sternum and rib, particularly in the context of multiple thoracotomies during his complicated admission. Therefore we recommend that patients about to embark on cancer chemotherapy or other immunosuppression should receive detailed education about the importance of minimising specific environmental exposures to avoid colonisation with Scedosporium spp. and other pathogenic fungi.

Successful treatment in our patient involved combination voriconazole and terbinafine therapy as well as adjunctive surgical drainage and debridement. The presence of culture-positive tissue from his sternum and rib four months after commencing combination therapy highlights the importance of surgical debridement as a management strategy in these patients. Although there was clinical suspicion of sternal osteomyelitis when his wound dehisced, the absence of diagnostic radiologic findings made it difficult to persuade the surgeons to perform aggressive debridement. The patient's poor performance status and multiple previous thoracotomies were also barriers to early surgical debridement. Once surgery was eventually performed, clinical evidence of successful disease control were wound healing and a dramatic improvement in inflammatory markers. No further tissue specimens obtained after this time demonstrated any evidence of fungal invasion or were culture positive for S. prolificans.

Despite initial voriconazole toxicity with intravenous loading, there were significant difficulties in maintaining therapeutic plasma voriconazole levels. Whilst there are conflicting findings from clinical studies when correlating voriconazole levels and risk of hepatotoxicity [14,15], reduced voriconazole efficacy and poor outcomes have been associated with low plasma or serum levels, particularly with concentrations less than 1 mg/L [15–18]. Even with fixed voriconazole dosing, significant inter-patient and intra-patient variability of voriconazole concentrations has been reported [16,19]. Polymorphisms in CYP2C19, one of the major cytochrome P450 enzymes responsible for voriconazole clearance, may lead to poor or rapid metabolism and altered drug concentrations. Mulanovich et al. noted that voriconazole concentrations appeared to decline with prolonged treatment [19], particularly with treatment durations greater than 2 months. Autoinduction has also been described in animal models, and was reported by Moriyama et al. [20] in a patient with accelerated voriconazole metabolism where serum concentrations were restored with the addition of the CYP2C19 inhibitor cimetidine. CYP2C19 genotyping was not performed in our patient, however given that the difficulties in maintaining therapeutic voriconazole concentrations occurred several months into treatment, we hypothesise that autoinduction was the likely explanation. Addition of an alternative CYP2C19 inhibitor (pantoprazole) in our patient led to initial improvement in voriconazole levels but ultimately there remained difficulty in maintaining adequate concentrations remained difficult, even with 500 mg twice-daily dosing. Furthermore he exhibited significant hepatotoxicity without supratherapeutic levels and later developed peripheral neuropathy from prolonged use.

This case highlights locally extensive and angio-invasive S. prolificans infection in a patient with lung carcinoma who received successful combination treatment with voriconazole and terbinafine but ultimately succumbed to metastatic lung carcinoma. Notably there was an absence of predictable risk factors such as neutropenia, corticosteroids, diabetes or ongoing immunosuppression. Treatment was complicated by difficulties in maintaining therapeutic plasma voriconazole concentrations, even with the co-administration of a CYP2C19 inhibitor, as well as progressive cholestatic liver function abnormalities and peripheral sensory neuropathy. We feel this case emphasises the utility of combination antifungal treatment with adjunctive surgical debridement, reinforces the need for patient education to minimise potential environmental exposure, and highlights some difficulties in therapeutic drug monitoring.

Conflict of interest

N.E.H. is supported by a National Health and Medical Research Council postgraduate scholarship. S.E.K. is a member of the scientific advisory board for Pfizer.