A case of pulmonary Mycobacterium kansasii presenting with an atypical extensive consolidation involving the entire right lower lobe

Abstract

A 76-year-old man with a 3-year history of total gastrectomy presented with extensive consolidation involving the entire right lower lobe on chest CT. Pulmonary Mycobacterium kansasii infection was diagnosed based on sputum and bronchoscopic specimen analyses. Treatment with rifampicin, ethambutol, and clarithromycin was initiated, resulting in improvement of symptoms and radiography findings. M. kansasii infection typically presents with thin-walled cavities in the upper lung lobes. We report a rare case of atypical radiological findings characterized by extensive consolidation in the right lower lobe.

1. Introduction

Mycobacterium kansasii infection most commonly occurs in the upper lung lobes and is frequently associated with cavitary lesions; lower lobe involvement is uncommon [1,2]. Reports of extensive consolidation involving an entire lower lobe are rare. In contrast, in patients with human immunodeficiency virus (HIV) infection, pulmonary M. kansasii infection often presents with infiltrates or nodules in the middle and lower lung fields, differing from the typical upper-lobe cavitary lesions seen in those without HIV [3]. Here, we report a case of pulmonary M. kansasii infection in a patient without apparent immunodeficiency, who presented with extensive consolidation in a lower lobe, along with a review of the literature.

2. Case report

A 76-year-old Japanese man presented with a 1-month history of cough, sputum production, and fever (up to 38 °C). Chest radiography performed at a local clinic revealed extensive consolidation in the right lower lung field, accompanied by hypoxemia. He was referred to our hospital with suspected bacterial pneumonia. His medical history included total gastrectomy for gastric cancer 3 years earlier. He had no history of smoking or lung disease. Alcohol consumption was occasional.

On admission, his vital signs were as follows: height, 170.0 cm; weight, 50.5 kg (body mass index, 17.5 kg/m²); temperature, 37.7 °C; pulse rate, 100 beats/min (regular); blood pressure, 149/79 mmHg; respiratory rate, 20 breaths/min; and peripheral oxygen saturation, 90% on room air. Laboratory tests showed a white blood cell count of 5570/μL (neutrophils, 84.9%; lymphocytes, 5.6%; monocytes, 8.4%; and eosinophils, 0.7%) and a C-reactive protein level of 3.41 mg/dL, indicating inflammation (Table 1A). The serum albumin and total protein levels were 2.8 g/dL and 6.4 g/dL, respectively, indicating nutritional impairment. Chest radiography revealed consolidation, predominantly in the right lower lung field (Fig. 1A). Chest computed tomography (CT) revealed extensive consolidation with air bronchograms throughout the right lower lobe and a small cavitary lesion in segment 8 (Fig. 1B). In addition, high-contrast centrilobular nodules were observed, suggestive of mycobacterial infection.

Table 1.

Laboratory findings on admission: (A) blood test results and (B) sputum acid-fast bacillus examination results.

(A)
Peripheral blood		Biochemistry/Serology
White blood cells	5070/μL	TP	6.4 g/dL
Neutrophils	84.9%	Alb	2.8 g/dL
Lymphocytes	6.5%	AST	39 U/L
Monocytes	8.4%	ALT	23 U/L
Eosinophils	0.7%	LDH	413 U/L
Basophils	0.4%	T-Bil	0.3 mg/dL
Red blood cells	3.23 × 106/μL	BUN	21.4 mg/dL
Hemoglobin	10.2 g/dL	Cre	0.95 mg/dL
Platelets	322 × 103/μL	Na	138 mEq/L
		K	4.6 mEq/L
Infection markers		CRP	3.4 mg/dL
GPL core-IgA	negative	KL-6	2877 U/mL
T-SPOT.TB	negative	SP-D	1300 ng/mL
β-D-glucan	<6.0 pg/mL	IgG	1600 mg/dL
CMV-Ag	negative	IgA	359 mg/dL
Aspergillus-Ag	0.9 pg/mL	IgM	50 mg/dL
Aspergillus-Ab	7.7 AU/mL	APTT	27.0 sec
HIV-Ab	negative	PT-INR	0.95

(B)
AFB tests
Day 1
smear: negative	PCR: M. tuberculosis, M. avium, M. intracellulare (−)	culture: M. kansasii
Day 2
smear: 1+	PCR: M. tuberculosis, M. avium, M. intracellulare (−)	culture: M. kansasii
Day 3
smear: negative	PCR: M. tuberculosis, M. avium, M. intracellulare (−)	culture: M. kansasii

TP: Total protein, Alb: Serum albumin, AST: Aspartate aminotransferase, ALT: Alanine aminotransferase, LDH: Lactate dehydrogenase, T-Bil: Total bilirubin, BUN: Blood urea nitrogen, Cre: Serum creatinine, CRP: C-reactive protein, KL-6: Krebs von den Lungen-6, SP-D: Surfactant protein D, APTT: Activated partial thromboplastin time, PT-INR: Prothrombin time-international normalized ratio, GPL core IgA: Anti–glycopeptidolipid core immunoglobulin A antibody, β-D-glucan: (1 → 3)-β-D-glucan, CMV antigenemia: Cytomegalovirus pp65 antigenemia assay, Aspergillus Ab: Anti-Aspergillus antibody, Aspergillus Ag: Aspergillus galactomannan antigen, HIV Ab: Human immunodeficiency virus type 1/2 antibody.

Fig. 1.

Chest radiological findings on admission. (A) Chest radiography showing extensive consolidation predominantly in the right lower lung field. (B) Chest computed tomography revealing extensive consolidation with air bronchograms involving the entire right lower lobe, along with a small cavitary lesion in the lateral segment of S8. In addition, high-contrast centrilobular nodules (black arrows) are observed, suggestive of mycobacterial infection.

Given the 1-month duration of fever, history of gastrectomy, and cavitation on CT, pulmonary tuberculosis was considered. Three consecutive sputum samples were collected for acid-fast bacillus (AFB) testing. On hospital day 2, sputum AFB smear was positive (1+: 1-9 AFB per 10 fields), but polymerase chain reaction was negative for Mycobacterium tuberculosis, M. avium, and M. intracellulare (Table 1B). Based on the clinical history and imaging findings, empirical treatment for bacterial pneumonia was initiated with ampicillin/sulbactam (days 1–9), followed by tazobactam/piperacillin (days 10–14). However, the fever persisted, and chest radiography findings showed only minimal improvement.

The differential diagnoses for antibiotic-resistant pneumonia included organizing pneumonia (elevated KL-6 and SP-D levels), pulmonary aspergillosis (positive antigen and antibody tests), and nontuberculous mycobacterial infection (positive AFB smear). No bacteria, other than AFB, were detected in the sputum. Bronchoalveolar lavage (BAL) and transbronchial lung biopsy were performed on hospital day 18. BAL culture yielded M. kansasii (Table 2), and histopathology revealed epithelioid granulomas with multinucleated giant cells, caseous necrosis, and lymphocytic infiltration (Fig. 2A). Ziehl–Neelsen staining confirmed the presence of AFB (Fig. 2B). No fungal organisms were detected, and the findings did not support a diagnosis of organizing pneumonia.

Table 2.

Findings of bronchoalveolar lavage fluid (BALF) analysis and bronchial lavage culture. BALF was collected from the right B8a segment. No bacteria other than acid-fast bacillus were detected.

BALF findings (rB8a)
Fluid recovery rate	23 mL/150 mL	AFB tests
Total number of cells	54 × 105/mL	smear: 1+
Macrophages	1%	PCR: M. tuberculosis, M. avium, M. intracellulare (−)
Lymphocytes	3%	culture: M. kansasii
Neutrophils	96%
Eosinophils	0%

Fig. 2.

Histopathological findings of transbronchial lung biopsy. (A) Hematoxylin and Eosin stain (×10). Caseous necrosis with surrounding epithelioid granulomas and scattered multinucleated giant cells, along with lymphocyte-predominant inflammatory cell infiltration are observed. (B) Ziehl–Neelsen staining (×600) reveals the presence of acid-fast bacillus (black arrow).

Thus, the pulmonary infiltrates were attributed to M. kansasii. Cultures from three sputum samples were positive for M. kansasii. On hospital day 22, treatment with rifampicin (600 mg/day), ethambutol (750 mg/day), and clarithromycin (800 mg/day) was initiated. Drug susceptibility testing showed a minimum inhibitory concentration of 0.25 μg/mL for rifampicin, indicating susceptibility. The patient was discharged on day 32 without adverse effects. After 6 months of treatment, follow-up CT demonstrated marked improvement (Fig. 3), symptom resolution, normalized inflammatory marker levels, and negative sputum cultures.

Fig. 3.

Chest computed tomography findings 6 months after treatment initiation. Marked improvement in consolidation is observed in the right lower lobe. Residual cavitary lesions and bronchiectasis are also observed.

3. Discussion

M. kansasii is a nontuberculous mycobacterium (NTM) found in soil, dust, and water, but it is most often isolated from treated water sources [4]. Untreated pulmonary infection typically progresses to chronic disease, leading to destruction of the lung structure; therefore, most patients require antimicrobial therapy [5]. Risk factors for M. kansasii infection include heavy smoking, chronic obstructive pulmonary disease, alcoholism, prior gastrectomy, immunodeficiency, and prior tuberculosis [6]. Although gastrectomy has been associated with an increased risk of pulmonary tuberculosis, Kim et al. reported that the standardized incidences of NTM lung infection and disease after gastrectomy were not significantly different from those in the general population [7]. Therefore, the history of total gastrectomy in the present case should be regarded as a possible contributing factor through its association with nutritional impairment, rather than as an established risk factor for pulmonary M. kansasii infection.

The diagnosis, which was based on radiological findings, positive sputum cultures, and positive BAL culture, fulfilled the diagnostic criteria of the American Thoracic Society/Infectious Diseases Society of America released in 2007 [8]. Bronchoscopy excluded pulmonary aspergillosis and organizing pneumonia. The marked improvement with rifampicin, ethambutol, and clarithromycin without antifungal or steroid therapy further supported the diagnosis of M. kansasii as the sole pathogen.

Typically, pulmonary M. kansasii infection manifests as cavitary lesions in the upper lung lobes [1,2]. A Japanese study of 29 cases reported cavities in 82.8% of cases, predominantly in the upper lobes [9], although lower lobe involvement was noted. However, none of the patients exhibited extensive consolidation involving an entire lower lobe. Similarly, a Brazilian study of 19 cases reported large infiltrates but not in the lower lobes [10]. Notably, HIV-associated cases often exhibit middle and lower lung involvement [3]. Our patient had no evidence of HIV infection or immunodeficiency.

A literature search did not identify any non-HIV cases of M. kansasii infection presenting with extensive consolidation of an entire lower lobe. Although similar findings have been reported in disseminated disease with anti-interferon-γ autoantibodies and mixed infection [11], our case did not have systemic features.

Although Aspergillus antigen and antibody tests were positive, no fungal organisms were identified, and radiological evidence of improvement was noted without antifungal therapy. However, post-mycobacterial lung abnormalities may predispose individuals to chronic pulmonary aspergillosis [12], warranting continuous surveillance.

4. Conclusions

We report a rare case of pulmonary M. kansasii infection presenting with extensive consolidation involving an entire lower lobe. Treatment with rifampicin, ethambutol, and clarithromycin resulted in marked improvement. Bronchoscopy excluded other conditions such as organizing pneumonia and pulmonary aspergillosis. Although prior gastrectomy and nutritional impairment may have contributed to host susceptibility, a direct causal relationship with pulmonary M. kansasii infection could not be established, and there was no evidence of concurrent HIV infection or disseminated disease. To our knowledge, such presentation is rare in immunocompetent patients.

CRediT authorship contribution statement

Konjo Cho: Writing – review & editing, Writing – original draft, Conceptualization. Hirofumi Kamata: Writing – review & editing, Writing – original draft, Supervision, Project administration, Conceptualization. Yoshitaka Uchida: Writing – review & editing, Investigation, Conceptualization. Koji Okudela: Writing – review & editing, Visualization, Investigation. Fumikazu Sakai: Writing – review & editing, Visualization, Conceptualization. Makoto Nagata: Writing – original draft, Supervision, Conceptualization. Hidetoshi Nakamura: Writing – review & editing, Supervision, Conceptualization.

Funding

This report did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of competing interests

None of the authors have any conflicts of interest or financial ties to disclose.