Detection of Irpex lacteus in the Lung in a Case with Microscopic Polyangiitis-mimicking Manifestations Positive for Myeloperoxidase-antineutrophil Cytoplasmic Antibody

Abstract

Antineutrophil cytoplasmic antibody (ANCA) testing is valuable for the diagnosis of ANCA-associated vasculitis; however, ANCA can be positive in infectious diseases. We herein report a case of myeloperoxidase (MPO)-ANCA-positive microscopic polyangiitis-mimicking manifestations in which the bronchoalveolar lavage was positive for Irpex lacteus. After initiating treatment for I. lacteus with isavuconazole, the patient's symptoms of pain in the lower legs improved, and MPO-ANCA became negative. This case provides speculation on the relationship between fungus and ANCA production and highlights the importance of an exhaustive search for infectious agents when administering immunosuppressive therapies.

Introduction

Antineutrophil cytoplasmic antibody (ANCA) is an important indicator for the diagnosis and differentiation of ANCA-associated vasculitis (AAV) and is included in the current classification criteria for the disease (1-6). Myeloperoxidase (MPO)-ANCA and proteinase 3-ANCA are closely related to microscopic polyangiitis (MPA) and granulomatosis with polyangiitis, respectively (1-3). However, diseases other than MPA and various infectious diseases have also been reported to induce MPO-ANCA production. Aspergillus, Histoplasma, and Pneumocystis are reportedly associated with MPO-ANCA positivity (3). Therefore, exclusion of infectious diseases is mandatory before administering immunosuppressive agents.

We herein report a case of MPO-ANCA-positive MPA-mimicking manifestations of Irpex lacteus detected in the bronchoalveolar lavage (BAL) fluid.

Case Report

A 69-year-old Japanese man experienced a fever and pain in both the shoulders and lower legs. He had previously been diagnosed with polymyalgia rheumatica and started treatment with prednisolone (PSL) at 20 mg/day. The patient's symptoms improved, but the elevated C-reactive protein (CRP) levels persisted. A urinalysis revealed a red blood cell (RBC) count of 30-49/high-power field (HPF). Further investigations revealed MPO-ANCA positivity and peripheral neuropathy, as suggested by numbness in the bilateral lower legs. The patient was referred to our hospital for a further evaluation of AAV one month after the first appearance of symptoms.

He had a medical history of pulmonary tuberculosis (TB) approximately 40 years ago and stopped treatment at his discretion after 3 months of inpatient treatment. He had smoked 30 cigarettes a day for 40 years until 15 years ago. The patient lived in an 80-year-old wooden house with poor sunlight.

On admission, he was 172 cm tall, weighed 43.5 kg, and his vital signs were as follows: blood pressure, 111/61 mmHg; pulse rate, 75 beats/min; and body temperature, 36.7°C. On chest auscultation, the patient had normal alveolar breath sounds but no adventitious sounds. No skin rash was observed. Manual muscle testing revealed weakness in the biceps brachii, triceps brachii, iliopsoas, quadriceps, and thigh flexor muscles in 4/4. No normal bilateral patellar tendon reflexes were observed. However, no obvious paralysis or sensory disturbances were observed.

Laboratory findings on admission were as follows: high CRP (12.6 mg/dL) and interleukin-6 (165 pg/mL), positive rheumatoid factor (98.2 U/mL), and positive MPO-ANCA (55.2 U/mL) with PSL 20 mg/day. There was no elevation in muscle-derived enzymes, such as creatine kinase or aldolase. Antinuclear antibodies showed a speckled pattern with a titer of 1:80. A T-SPOT TB interferon-gamma release assay, β-D-glucan, Aspergillus antigen, Cryptococcus antigen, and other infectious diseases were negative (Table 1). A urinalysis revealed an RBC count of 5-9/HPF. Peripheral nerve conduction velocity studies showed latency prolongation, decreased conduction velocity, and decreased amplitude in the left median, left ulnar, left tibial, and peroneal nerves, findings consistent with mononeuritis multiplex. Chest computed tomography revealed infiltrative opacity in both lung apexes (Fig. 1A). Ground-glass opacity was also observed in the left lower lobe, which was consistent with interstitial lung disease (Fig. 1B). Neither a histological examination nor ANCA testing using indirect immunofluorescence was performed in this patient.

Table 1.

Laboratory Data at the Inpatient Examination.

CBC				Chemistry				Infection
WBC	8,600	/μL		TP	7.5	g/dL		β-D-glucan	4.4	pg/mL
Neutrophil	92.0	％		Alb	1.9	g/dL		Candida antigen	(-)
Lymphocyte	2.0	％		Na	137	mEq/L		Aspergillus antigen	(-)
Monocyte	5.0	％		K	3.6	mEq/L		Cryptococcal antigen	(-)
Eosinophil	1.0	％		Cl	102	mEq/L		Interferon-gamma release assays	(-)
Basophil	0.0	％		BUN	28	mg/dL		HBs antigen	(-)
RBC	5.20×106	/μL		Cr	0.60	mg/dL		HBs antibody	(-)
Hb	14.0	g/dL		eGFR	100.64	mL/min/1.73m2		HBc antibody	(-)
Hct	44.8	％		T-Bil	0.3	mg/dL		HCV antibody	(-)
PLT	20.0×104	/μL		AST	72	U/L		Blood culture	(-)
				ALT	202	U/L
Urinalysis				ALP	149	U/L		Immunology
Dipstick urine test				LDH	153	U/L		IgA	320	mg/dL
Protein	1+			CRP	12.62	mg/dL		IgG	1,988	mg/dL
Hematuria	2+			GLU	95	mg/dL		IgM	77.5	mg/dL
Sediment				Ferritin	871	ng/mL		MPO-ANCA	55.2	U/mL
WBC	<1	/HPF		sIL-2R	1,540	U/mL		PR3-ANCA	<1.0	U/mL
RBC	5-9	/HPF		IL-6	165	pg/mL		anti-GBM antibody	<1.5	U/mL
Hyaline casts	1-4	/HPF		KL-6	174	U/mL
Epithelial casts	5-9	/HPF
Waxy casts	1-4	/HPF
Urine protein/creatinine	0.31	g/g･Cr

Alb: albumin, ALP: alkaline phosphatase, ALT: alanine aminotransferase, AST: aspartate aminotransferase, BUN: blood urea nitrogen, CBC: complete blood count, Cl: chloride ion, Cr: creatinine, CRP: C-reactive protein, eGFR: estimated glomerular filtration rate, GBM: glomerular basement membrane, GLU: glucose, Hb: hemoglobin, HBc: hepatitis B core, HBs: hepatitis B surface, HCV: hepatitis C virus, Hct: hematocrit, HPF: high-power field, IgA: immunoglobulin A, IgG: immunoglobulin G, IgM: immunoglobulin M, IL-6: interleukin-6, K: potassium, LDH: lactate dehydrogenase, MPO-ANCA: myeloperoxidase anti-neutrophil cytoplasmic antibody, Na: sodium, PLT: platelet, PR3-ANCA: proteinase 3-anti-neutrophil cytoplasmic antibody, RBC: red blood cell, sIL-2R: soluble interleukin-2 receptor, T-Bil: total bilirubin, TP: total protein, WBC: white blood cell

Figure 1.

Infiltrative opacity in both lung apexes on CT (A, red arrows), and ground-glass opacity in the left lower lobe on CT (B, red arrow) before treatment with ISCZ. No changes were noted in the infiltrative opacity in either lung apex on chest CT four months after initiating ISCZ (C). Improvement of ground-glass opacity on chest CT was noted four months after initiating ISCZ (D).

The patient was initially considered to have MPA based on the 2012 Revised International Chapel Hill Consensus Conference Nomenclature of Vasculitides (4) and the European Medicines Agency algorithm (5). In addition, based on the American College of Rheumatology/European Alliance of Associations of Rheumatology classification criteria (2022) (6), the patient was classified as having MPA with a total score of nine points.

Bronchoscopy was performed to exclude active TB, as the patient had a history of TB. A BAL fluid examination was negative for acid-fast bacilli smear, polymerase chain reaction for Mycobacterium tuberculosis and M. avium complex, and Aspergillus fumigatus. No bacteria were detected in the sputum specimens using conventional culture methods. Filamentous fungi were detected in the BAL, but the species could not be identified using conventional culture methods. Therefore, we performed a sequence analysis of the internal transcribed spacer and D1/D2 regions using pellets from BAL to identify fungal pathogens. As a result, the filamentous fingi was identified as Irpex lacteus.

For this analysis, genomic DNA was extracted using ISOPLANT II (NIPPON GENE, Tokyo, Japan), and the D1/D2 region was amplified and sequenced using the Fungal rDNA (D1/D2) PCR Kit Fast (Takara Bio, Shiga, Japan) according to the manufacturer's instructions. This method can detect bacteria and fungi that are slow-growing and difficult to detect using conventional culture methods (7-9). Antifungal treatment must be initiated before definitive identification of the causative organism. Because tests were negative for both Aspergillus and Cryptococcus antigens, mucormycosis was considered as a differential diagnosis.

As voriconazole is ineffective against mucormycosis, isavuconazole (ISCZ), an orally available antifungal treatment effective against Mucor species, was selected. Considering the anticipated need for prolonged treatment, amphotericin B, which is only available as an intravenous formulation, was not used. ISCZ was administered at a dose of 200 mg once every 8 h for 6 doses, followed by a dose of 200 mg once daily for 6 months. As PSL was started by the previous physician and tapered gradually, CRP levels and MPO-ANCA titers declined. However, his clinical course appears to be different from that of typical MPA since CRP levels and MPO-ANCA titers decreased rapidly by ISCZ, even with low-dose PSL. Therefore, we concluded that this patient had MPA-mimicking manifestations associated with I. lacteus infection, and additional immunosuppressive treatment was postponed because of concerns regarding the exacerbation of infection by I. lacteus.

Two months after starting treatment with ISCZ, the pain in both lower extremities improved, and MPO-ANCA and CRP levels were negative in the following months. The urinalysis abnormalities returned to normal levels. In addition, although the infiltrative opacity in both lung apexes did not change (Fig. 1C), ground-glass opacity on chest computed tomography improved (Fig. 1D). We suspect that infiltrative opacities in both lung apices were previous TB changes because these opacities showed no significant radiological changes with antifungal therapy over the clinical course. It was also considered possible that I. lacteus had been present in the lung apices with previous tuberculous lesions. In contrast, ground-glass opacities are presumed to reflect an MPA-mimicking pathophysiology and improve with PSL treatment. The patient stopped taking PSL the following month and did not experience any relapse (Fig. 2).

Figure 2.

Clinical course of the patient after admission.

Discussion

I. lacteus is a white-rot fungus of the phylum Basidiomycota that colonizes dead branches and trunks of deciduous trees and is distributed globally throughout the year (10). To date, four cases of I. lacteus infection manifesting as pulmonary abscesses and meningitis have been documented in the literature (11-14). All affected patients received underlying immunosuppressive therapy or had pre-existing pulmonary disease. The treatment regimens included voriconazole and amphotericin B (Table 2).

Table 2.

Reported Cases of Irpex lacteus Infection.

No.	Ref.	Age/Sex	Background disease	Presentation	Inspection	Treatment	Outcome
1	(8)	17/F	After lung transplant	Fever, difficulty breathing, deoxygenation	BAL fluid	Voriconazole	deteriorated
2	(9)	9/F	Acute leukemia	Fever, pulmonary nodules	Chest CT-guided biopsy	Amphotericin B	improved
3	(10)	64/F	Rheumatoid arthritis, pulmonary tuberculosis	Pneumonia, cough, dyspnea	BAL fluid	Voriconazole	improved
4	(11)	73/M	Sarcoidosis	Fungal meningitis, fever, increased CRP, anemia	CSF	Amphotericin B	improved

BAL: bronchoalveolar lavage, CT: computed tomography, CSF: cerebrospinal fluid

The relationship between MPO and ANCA production and the detection of I. lacteus is intriguing when speculating on the pathogenesis and mechanism of this case. Neutrophil extracellular traps (NETs) play a major role in AAV pathogenesis (15). Neutrophils are activated, and NETs are induced by bacterial, fungal, and parasitic infections (16). Extracts of I. lacteus have been reported to activate toll-like receptor 4 (TLR4) (17), which drives NET formation (18). TLR4 is expressed in neutrophils. In addition, NETs form when neutrophils undergo phagocytosis induced excessive neutrophil activation (15).

Based on these studies, we speculated that I. lacteus might activate TLR4 on neutrophils, which induces NET formation, leading to an MPA-mimicking pathophysiology. In addition, the infected fragile lung tissue after pulmonary TB may have provided I. lacteus with an appropriate environment for localization.

I. lacteus may also have been responsible for the ANCA positivity and contributed to the induction of MPA-like pathogenesis because the patient showed improvement in clinical symptoms and tested negative for CRP and MPO-ANCA after treatment with ISCZ. Furthermore, no relapse was observed after discontinuation of PSL. To our knowledge, there are no reports of MPO-ANCA-positive I. lacteus infection. Our case is valuable in considering MPA-like pathophysiology.

In conclusion, ANCA positivity due to infection should be considered in AAV patients. Therefore, a comprehensive evaluation of infectious agents, including bronchoscopy, should be performed before initiating treatment with immunosuppressive agents.

The authors state that they have no Conflict of Interest (COI).