ATS/JRS/ALAT Hypersensitivity Pneumonitis Guidelines for Diagnosis of humidifier lung and summer-type hypersensitivity pneumonitis

BACKGROUND

The ATS/JRS/ALAT Guidelines for the Diagnosis of Hypersensitivity Pneumonitis (GL for HP) were published in 2020. Humidifier lung and summer-type HP are forms of HP, but it is unclear whether they can be diagnosed using GL for HP. This study examined the level of confidence where humidifier lung and summer-type HP can be diagnosed with GL for HP.

METHODS

Data from 23 patients with humidifier lung and 20 patients with summer-type HP (mean age, 67.3 and 57.4 years, respectively) diagnosed between October 2012 and January 2022 were retrospectively reviewed. We evaluated high resolution computed tomography (HRCT) patterns, bronchoalveolar lavage fluid (BALF) findings, exposures, and histopathological findings to determine the level of confidence where a diagnosis of HP could be made using the GL for HP.

RESULTS

HRCT pattern was classified as typical HP in 5 (22%) and compatible with HP in 18 (78%) patients with humidifier lung and considered as typical HP in 17 (85%) and compatible with HP in 3 (15%) patients with summer-type. The confidence level for diagnosis of HP was definite in 2 (8.7%), moderate in 14 (60.9%), and low in 7 (30.4%) patients with humidifier lung. It was definite in 12 (60%), high in 3 (15%), and moderate in 5 (25%) patients with summer-type HP.

CONCLUSIONS

GL for HP showed utility in diagnosing humidifier lung in many patients with a moderate to low confidence. However, there was a definite to high confidence for patients with summer-type HP.

Causative antigens of humidifier lung in vapor from a humidifier: A case report

A 68-year-old man exhibited fever and cough three weeks prior to hospital admission after three months of ultrasonic humidifier usage. Chest computed tomography showed bilateral ground-glass opacities, lymphocyte levels in the bronchoalveolar lavage fluid were elevated (60.8%), and the histological examination of a transbronchial lung biopsy showed lymphocytic alveolitis. He gradually improved without medication after he stopped using the humidifier. Accordingly, humidifier lung was the diagnosis. Humidifier water and vapor collected from the patient's humidifier were investigated. Humidifier vapor was obtained by collecting the condensed moisture. Laboratory examinations exhibited gram-negative rods and a high concentration of endotoxin and (1 → 3)-β-D-glucan in both vapor and water. The serum-precipitating antibodies showed a stronger reaction against humidifier vapor than against humidifier water. 16S rRNA metagenomic analysis revealed a high percentage of sequences of Spirosoma lacussanchae and Sphingomonas spp. in both the humidifier vapor and water. The percentages of sequence reads were lower in humidifier vapor than in water; conversely, sequences of Pseudomonas spp. and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium were more concentrated in the humidifier vapor than in humidifier water. Although the reason for the different bacterial ratios between humidifier vapor and water is uncertain, the bacteria that were more concentrated in humidifier vapor than in humidifier water might have been the causative antigen underlying the humidifier lung diagnosis. This is the first report to indicate the presence of causative antigens in humidifier vapor.

Clinical and radiological characteristics of ultrasonic humidifier lung and summer-type hypersensitivity pneumonitis

BACKGROUND

Ultrasonic humidifier lung is a rare form of hypersensitivity pneumonitis (HP), and its clinical and radiological features are unclear. This study examined the clinical and radiological characteristics of humidifier lung.

METHODS

Data from 18 patients with humidifier lung (mean age, 67.3 years) diagnosed during October 2012 through April 2018 were retrospectively reviewed. We compared clinical, laboratory, and CT findings and bronchoalveolar lavage fluid (BALF) characteristics of these patients with those of 19 patients with summer-type HP (mean age, 57.4 years).

RESULTS

Cough and dyspnea were the most common symptoms. White blood cell count and serum C-reactive protein titers were higher for humidifier lung than for summer-type HP. Serum levels of Krebs von den Lungen-6 and surfactant protein D were significantly lower for humidifier lung than for summer-type HP. The most common chest CT findings in humidifier lung were ground-glass opacities (88.9%) and mosaic attenuation (50.0%). Centrilobular ground glass nodules were less common in humidifier lung than in summer-type HP (27.8% vs 63.1%; P = 0.043). Peribronchovascular or subpleural nonsegmental consolidation was more frequent in humidifier lung than in summer-type HP (44.4% vs 5.3%; P = 0.013). Lymphocyte fractions in BALF specimens were significantly lower for humidifier lung than for summer-type HP (37.3% vs 69.0%; P < 0.001). Neutrophil fractions were higher for humidifier lung, but the difference was not significant (22.1% vs 8.1%; P = 0.153). The CD4/8 ratio was higher for humidifier lung than for summer-type HP (1.7 vs 0.8; P = 0.003).

CONCLUSIONS

The clinical and radiological characteristics of humidifier lung differ from those of summer-type HP.