Features of humidifier lung and comparison with summer-type hypersensitivity pneumonitis

Recurrent episodes of febrile dyspnoea: hypersensitivity pneumonitis caused by a household ultrasonic humidifier

Hypersensitivity pneumonitis is an immune-mediated interstitial lung disease that presents with respiratory symptoms, with or without systemic symptoms, following exposure to an identified or unidentified external factor. It can be caused by extrinsic factors including household items such as ultrasonic humidifiers.We present an intriguing case of a previously healthy 50-year-old man who displayed recurrent episodes of progressive dyspnoea and fever after repeated exposure to his household ultrasonic humidifier. He was treated with corticosteroids, followed by the removal of the humidifier, resulting in total recovery and absence of recurrence of further episodes.The clinical presentation of hypersensitivity pneumonitis can be dramatic, and the differential diagnosis is broad. The correct diagnosis is achieved by combining clinical, radiological and histopathological patterns. The key to finding the aetiology lies in a thorough history, with an important role for household investigations to identify the external factor.

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.

A case of humidifier lung; the key diagnosis is detailed medical history taking

A 74-year-old woman was admitted with a dry cough and dyspnea that had persisted for 2 weeks at the beginning of winter. Chest computed tomography revealed bilateral diffuse non-segmental ground-glass opacities without centrilobular nodules. Bronchoalveolar lavage fluid revealed a marked increase in the lymphocyte ratio. Her condition and chest radiographic findings improved spontaneously after admission. An additional interview conducted after admission revealed that the patient had started using a contaminated humidifier approximately 2 weeks before the onset of symptoms. Thus, the diagnosis of humidifier lung was established. Humidifier lung is a rare phenotype of hypersensitive pneumonitis that often occurs during dry winter when the use of humidifiers increases. Humidifier lung is an important differential diagnosis of bilateral pneumonia during dry winter, and detailed history-taking regarding the use of humidifiers, assuming a humidifier lung, is crucial for its diagnosis.

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.

A case of humidifier lung with a difficult differential diagnosis from COVID-19

Acute respiratory illnesses that presented with diffuse ground-glass opacities (GGOs) on chest computed tomography (CT) scan suggest the diagnosis of coronavirus disease 2019 (COVID-19). However, many other diseases show similar CT findings, which often offer a difficult differential diagnosis. Here, we report a case of humidifier lung, a rare phenotype of hypersensitivity pneumonitis (HP), which mimicked COVID-19. A 71-year-old man was admitted because of dyspnea and diffuse GGOs found on chest CT scan. Although COVID-19 was initially suspected, his symptoms rapidly improved by the next day. A medical interview revealed that he had started using an ultrasonic humidifier 1 month ago. A high-resolution CT (HRCT) scan showed ill-defined centrilobular nodules and mosaic attenuation, which are typical of HP but atypical of COVID-19. The inhalation challenge test confirmed the diagnosis of humidifier lung. History-taking of humidifier use and a precise HRCT interpretation are helpful to differentiate it from COVID-19.