A Suspected Case of Allergic Bronchopulmonary Mycosis Associated With Exophiala dermatitidis

ABSTRACT

Exophiala dermatitidis is a black fungus that can colonize the airways, but allergic bronchopulmonary mycosis (ABPM) associated with E. dermatitidis is rare. An 83‐year‐old former smoker without asthma presented with exertional dyspnea. Chest CT showed bronchiectasis and a mucus plug in the left B³ bronchus. One month after discharge for acute cholecystitis, he returned with cough. Chest CT showed enlargement of the mucus plug and an infiltrative shadow in the left upper lobe. Despite piperacillin/tazobactam therapy for suspected bacterial pneumonia, cough and radiological findings persisted. Laboratory findings showed eosinophilia of 546/μL and total IgE of 823 IU/mL. Bronchoscopy on hospital day 4 revealed the mucus plug, and cultures yielded E. dermatitidis. ABPM associated with E. dermatitidis was suspected. Corticosteroid and voriconazole therapy improved cough, radiological findings and eosinophilia. This case suggests E. dermatitidis may be involved in ABPM, even without cystic fibrosis.

An 83‐year‐old man without asthma developed allergic bronchopulmonary mycosis (ABPM) associated with Exophiala dermatitidis. This case suggests that E. dermatitidis may be involved in ABPM.

1. Introduction

Exophiala dermatitidis is a black fungus found in moist environments and colonizes the airways, particularly in patients with cystic fibrosis (CF) [1]. Recently, E. dermatitidis has been increasingly recognized as a pulmonary pathogen, especially in patients with underlying pulmonary disease, immunosuppression or bronchiectasis [2]. In contrast, allergic bronchopulmonary mycosis (ABPM) associated with E. dermatitidis has rarely been reported [3].

2. Case Report

An 83‐year‐old man, a former smoker with a 15‐pack‐year smoking history, had diabetes mellitus and hyperlipidemia but no history of asthma or other allergic diseases. He presented to our hospital with exertional dyspnea. His peripheral oxygen saturation (SpO₂) was 93% on room air, and his respiratory rate (RR) was 16 breaths/min. Chest computed tomography (CT) showed bronchiectasis and a mucus plug in the left B³ bronchus (Figure 1A,B). The results of pulmonary function testing were as follows: forced vital capacity (FVC), 4.0 L; percent predicted FVC, 118.3%; forced expiratory volume in 1 s (FEV₁), 3.38 L; percent predicted FEV₁, 128.5%; and FEV₁/FVC ratio, 84.5%. No wheezing was heard, and pulmonary function testing showed no evidence of obstructive ventilatory impairment. The cause of the mild hypoxemia remained unclear, and bronchoscopy was scheduled to further investigate the bronchial abnormalities. However, it was postponed because he was admitted to our hospital due to acute cholecystitis. He was treated with cefmetazole and underwent laparoscopic cholecystectomy, followed by treatment with piperacillin/tazobactam (PIPC/TAZ), which was later switched to cefepime. He was discharged 11 days postoperatively.

FIGURE 1.

(A, B) Chest CT images at the initial visit show a mucus plug in the left B³ bronchus. (C, D) Chest CT at admission for suspected ABPM shows an infiltrative shadow in the left upper lobe. High‐attenuation mucus is not observed. (E) Bronchoscopic image shows a mucus plug in the left B³ bronchus (arrowhead). Chest CT images before (F) and 12 days after (G) initiation of corticosteroid and voriconazole therapy.

One month later, he returned to our hospital with a cough. His body temperature was 36.1°C, SpO₂ was 96% on room air, and RR was 16 breaths/min. No wheezing was heard. Laboratory findings are shown in Table 1. A white blood cell count was 5000/μL, an eosinophil count of 320/μL, and a C‐reactive protein level of 1.63 mg/dL. Chest CT showed enlargement of the mucus plug and an infiltrative shadow in the left upper lobe, without high‐attenuation mucus (HAM) (Figure 1C,D). He was admitted with suspected bacterial pneumonia, and PIPC/TAZ was initiated. However, his cough persisted, and chest X‐ray on hospital day 4 showed no improvement. Therefore, bronchoscopy was performed, revealing the mucus plug in the left B³ bronchus (Figure 1E), which was aspirated and submitted for cytological examination and culture. Chest CT on hospital day 9 showed a persistent infiltrative shadow in the left upper lobe despite continued PIPC/TAZ therapy (Figure 1F). Subsequent cytological evaluation of bronchoscopic specimens obtained on hospital day 4 revealed eosinophilic mucin and septate fungal hyphae with distinct branching. Charcot–Leyden crystals were not identified. Histopathological evaluation was not performed, and tissue invasion could not be assessed. Fungal culture was performed using potato dextrose chloramphenicol agar (Eiken Chemical, Tokyo, Japan) and incubated for 3–7 days at 35°C under aerobic conditions, yielding grey yeast‐like colonies that gradually turned black after 3–5 days [2]. Cultures yielded E. dermatitidis and concomitant Candida albicans . During hospitalization, the peripheral blood eosinophil count increased to a maximum of 546/μL and the total serum IgE level was 823 IU/mL. Specific IgE was negative for Alternaria, Aspergillus and Candida. Based on these allergic findings and the isolation of E. dermatitidis from bronchoscopic specimens, we suspected ABPM associated with E. dermatitidis rather than Candida. Intravenous methylprednisolone (mPSL) 35 mg and voriconazole (VRCZ) 600 mg were initiated on hospital day 11. Five days after corticosteroid and VRCZ initiation, his cough and chest X‐ray findings improved. mPSL was switched to prednisolone (PSL) and gradually tapered. Chest CT performed 12 days after corticosteroid and VRCZ initiation showed improvement of the infiltrative shadow (Figure 1G), and the peripheral blood eosinophil count had decreased. VRCZ was discontinued after 2 weeks of treatment due to renal dysfunction. After PSL was tapered to 10 mg/day, the patient was discharged on hospital day 36. PSL was discontinued approximately 4 months after discharge, with no worsening of cough or chest X‐ray during the subsequent 3‐month follow‐up. The clinical course is shown in Figure 2.

TABLE 1.

Laboratory findings at admission for suspected ABPM.

Haematology
WBC	5000	/μL
Neu	2160	/μL
Lym	2070	/μL
Eos	320	/μL
RBC	442 × 104	/μL
Hb	13.3	g/dL
Plt	185 × 103	/μL
Biochemistry and serology
TP	7.7	g/dL
Alb	3.8	g/dL
T‐bil	0.69	mg/dL
BUN	19.6	mg/dL
UA	4.6	mg/dL
Cre	0.82	mg/dL
eGFR	68	mL/min/1.732
Na	139	mmol/L
K	4.6	mmol/L
Cl	102	mmol/L
AST	38	U/L
ALT	29	U/L
LD	239	U/L
CK	39	U/L
CRP	1.63	mg/dL
PR3‐ANCA	< 1.0	U/mL
MPO‐ANCA	< 1.0	U/mL
β‐D glucan	5.1	pg/mL
Aspergillus galactomannan antigen	0.2
Aspergillus IgG antibody	< 1.4	AU/mL
Total serum IgE	823 (< 170)	IU/mL
Asp f 1‐specific IgE	< 0.10	UA/mL
Alternaria‐specific IgE	0	LC
Aspergillus‐specific IgE	0	LC
Candida‐specific IgE	0	LC
Cryptomeria japonica ‐specific IgE	15.30 (< 1.39)	LC
Dactylis glomerata ‐specific IgE	96.40 (< 1.39)	LC
Phleum pratense ‐specific IgE	93.20 (< 1.39)	LC
Urinary antigen tests
Streptococcus pneumoniae	Negative
Legionella pneumophila	Negative
Culture
Sputum	Normal respiratory flora
Bronchoscopy	Exophiala dermatitidis
	Candida albicans

Note: Values in parentheses indicate cut‐off values.

Abbreviations: Asp f 1, Aspergillus fumigatus allergen 1; LC, lumicount.

FIGURE 2.

The clinical course of the patient's symptoms, SpO₂, treatment and imaging findings.

3. Discussion

ABPM is an allergic pulmonary disorder that develops when fungi colonize the airways and induce an immune response against the colonizing fungus. Although our patient had no history of asthma or other allergic diseases, ABPM can occur in patients without underlying asthma [4]. Major causative fungi of ABPM other than Aspergillus include Bipolaris spp., Schizophyllum commune and Curvularia spp [3]. E. dermatitidis has also been suggested as a potential causative fungus of ABPM [5].

In this case, although HAM was not observed, bronchiectasis, a mucus plug in the left B³ bronchus, an infiltrative shadow on subsequent CT, elevated total IgE, peripheral blood eosinophilia, cytologically confirmed fungal hyphae, and isolation of E. dermatitidis from bronchial specimens led to a clinical suspicion of ABPM. As summarized in Table 2, the patient did not meet the 2024 ISHAM diagnostic criteria [3] because E. dermatitidis‐specific IgE, an essential component, could not be demonstrated. However, the patient fulfilled six components of the diagnostic criteria proposed by Asano et al. [6], and therefore met the diagnostic criteria for ABPM.

TABLE 2.

Comparison of the diagnostic criteria and their application to the present case.

Asano et al. [6]	ISHAM 2024 [3]	Present case
1. Current or previous history of asthma or asthmatic symptoms	Predisposing conditions (asthma, cystic fibrosis, chronic obstructive lung disease, bronchiectasis) or compatible clinico‐radiological presentation	No
2. Immediate cutaneous hypersensitivity or specific IgE for filamentous fungi	Essential component: Elevated fungus‐specific IgE.	Not assessed
3. Elevated total serum IgE levels (≥ 417 IU/mL)	Serum total IgE ≥ 500 IU/mL	Yes
4. Presence of precipitins or specific IgG for filamentous fungi	Other component: Positive fungus‐specific IgG	Not assessed
5. Peripheral blood eosinophilia (≥ 500 cells/mm3)	Blood eosinophil count ≥ 500 cells/μL (could be historical)	Yes
6. Filamentous fungal growth in sputum cultures or bronchial lavage fluid	Two sputum (or one bronchoalveolar lavage fluid) fungal cultures growing the causative fungus	Yes
7. Central bronchiectasis on CT	Thin‐section chest CT consistent with ABPA/ABPM (bronchiectasis, mucus plugging and high‐attenuation mucus) or fleeting opacities on chest radiograph	Yes
8. Presence of mucus plugs in central bronchi, based on CT/bronchoscopy or mucus plug expectoration history		Yes
9. High attenuation mucus in the bronchi on CT		No
10. Presence of fungal hyphae in bronchial mucus plugs		Yes
Patients that meet 6 or more criteria are diagnosed with ABPM. Filamentous fungi in the hypersensitivity, IgG/precipitin, and culture criteria should be identical.	Diagnosis requires predisposing conditions or compatible presentation, both essential components, and at least two other components. High‐attenuation mucus can confirm ABPM even if other criteria are not fulfilled.

Demonstration of sensitization to the causative fungus is essential for the diagnosis of ABPM; elevation of causative fungus‐specific IgE is regarded as an essential diagnostic component, and positive specific IgG serves as another component [3]. At present, research‐based measurement of E. dermatitidis‐specific IgE and IgG, including testing in collaboration with a mycology reference center, could not be performed. Therefore, sensitization to E. dermatitidis could not be demonstrated, which limits definitive attribution of ABPM to E. dermatitidis. However, Barrera et al. [5] recently detected elevated specific IgE and IgG against E. dermatitidis in patients with CF, which contributed to the diagnosis of ABPM. Although our case occurred in a patient without CF, their findings suggest that E. dermatitidis may act as a causative allergen in ABPM and provide indirect support for our clinical suspicion.

Only normal respiratory flora was detected in sputum cultures, whereas E. dermatitidis was isolated from bronchoscopic specimens, including the mucus plug. Although sputum culture is noninvasive, it is susceptible to contamination by commensal microorganisms of the upper airway. In contrast, bronchoscopy enables direct sampling of lower‐airway specimens with a lower risk of contamination. In a large survey by Tomomatsu et al. [7], mucus plugs were successfully obtained by bronchoscopy in 79% of patients with ABPA/ABPM. The fungal culture positivity rate using mucus plugs and bronchial lavage fluid was 46%, significantly higher than that of sputum cultures. Furthermore, pathological examination of the retrieved mucus plugs demonstrated fungal hyphae in approximately half of the cases (50%). These findings suggest that the combination of bronchoscopic fungal culture and pathological evaluation of mucus plugs contributes to the accurate diagnosis of ABPM. In addition, Yonezawa et al. [2] reported 13 cases of pulmonary infections caused by E. dermatitidis, in which this fungus was detected by bronchoscopy in six cases (46.2%) and by sputum culture in five cases (38.5%), suggesting the potential utility of bronchoscopy for detecting E. dermatitidis. In our case, fungal hyphae were confirmed cytologically, and E. dermatitidis was subsequently isolated from the mucus plug obtained by bronchoscopy. These findings were consistent with the diagnostic criteria proposed by Asano et al. [6]. However, histopathological evaluation was not performed, and tissue invasion could not be assessed, which represents a limitation of this case.

Both E. dermatitidis and C. albicans were isolated from the same bronchoscopic specimen. C. albicans is a yeast‐like fungus that has been reported as a causative organism of ABPM, although its pathogenic role remains controversial [3]. Furthermore, its true pathogenicity is uncertain, and it has been suggested that C. albicans is unlikely to induce the typical pathological features of ABPM [4]. In our case, no yeast cells were identified within the mucus plug, and Candida‐specific IgE was negative. Therefore, the involvement of C. albicans was considered less likely.

Corticosteroid therapy is generally used as the initial treatment for ABPM, with adjunctive antifungal therapy considered in selected cases [4]. Although the peripheral blood eosinophil count decreased and radiological findings improved after corticosteroid and VRCZ therapy, the independent contribution of VRCZ to these improvements remains unclear.

To our knowledge, this is the first case report suggesting the involvement of E. dermatitidis in ABPM in a patient without CF. When ABPM is clinically suspected and E. dermatitidis is isolated from airway specimens, its potential role as a causative fungus should be considered. However, isolation of E. dermatitidis alone does not establish it as the causative fungus, and careful differentiation from airway colonization is required based on the overall clinical, radiological, immunological, cytological and pathological findings. The availability of E. dermatitidis‐specific IgE and IgG assays may help clarify its pathogenic role in ABPM.

Author Contributions

T.Y. collected the clinical data and wrote the first draft. S.I. supervised the study. All the authors commented on earlier versions and approved the final manuscript.

Funding

The authors have nothing to report.

Consent

The authors declare that written informed consent was obtained for the publication of this manuscript and accompanying images using the consent form provided by the Journal.

Conflicts of Interest

The authors declare no conflicts of interest.

Yonezawa T., Onishi S., Sunakawa D., Kato Y., and Ito S., “A Suspected Case of Allergic Bronchopulmonary Mycosis Associated With Exophiala dermatitidis ,” Respirology Case Reports 14, no. 8 (2026): e70700, 10.1002/rcr2.70700.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.