{
  "abstract": "Background Humidifier lung (HFL) is a rare subtype of hypersensitivity pneumonitis (HP); understanding of the clinical, radiological and pathological characteristics is limited. To clarify the phenotype of HFL, this study compared HFL with the more established summer-type HP (SHP).Methods This nationwide survey of patients with HFL was conducted in 214 participating facilities across Japan from January 2011 to December 2021. Clinical, radiological and histopathological findings were comparatively evaluated between patients diagnosed with HFL and those with SHP.Results Overall, 430 HFL and 784 SHP cases were identified, with an increasing trend over time and a marked rise in HFL during the COVID-19 pandemic. Detailed data from 278 HFL and 220 SHP cases showed that HFL patients were older and predominantly male. HFL exhibited higher serum C-reactive protein levels but lower Krebs von den Lungen-6 (KL-6) and surfactant protein D levels than SHP (all p<0.0001).Chest CT in both cohorts included ground-glass opacities and mosaic attenuation; centrilobular ground-glass nodules were less frequent in HFL, which more frequently showed airspace consolidation.Histopathology demonstrated alveolitis in both with more intra-alveolar organisation and fewer epithelioid cell granulomas in HFL.Cluster analysis identified an HFL cluster with either Acute Respiratory Distress Syndrome (ARDS)-like or organising pneumonia-like high-resolution CT findings and normal KL-6, hence diagnosis can be challenging. Conversely, the major cluster of SHP showed typical CT features and elevated KL-6.Conclusions HFL exhibits distinct clinical, radiological and pathological characteristics compared to SHP, suggesting a unique subtype. This holds relevance for diagnostic accuracy and improved patient outcomes.",
  "authors": [
    {
      "affiliations": [
        "Department of Respiratory Medicine, Toho University Omori Medical Center, Ota, Japan"
      ],
      "name": "Susumu Sakamoto"
    },
    {
      "affiliations": [
        "Department of Pulmonary Medicine Thoracic Center, St Luke’s International Hospital, Chuo, Japan"
      ],
      "name": "Atsushi Kitamura"
    },
    {
      "affiliations": [
        "Department of Respiratory Medicine, Institute of Science Tokyo, Bunkyo-ku, Tokyo, Japan"
      ],
      "name": "Yuki Iijima"
    },
    {
      "affiliations": [
        "Division of Respiratory Medicine, Musashino Red Cross Hospital, Musashino, Japan"
      ],
      "name": "Satoko Hanada"
    },
    {
      "affiliations": [
        "Department of Respiratory Medicine, Seirei Mikatahara General Hospital, Hamamatsu, Japan"
      ],
      "name": "Koshi Yokomura"
    },
    {
      "affiliations": [
        "Respiratory Disease Center, Japan Anti-tuberculosis Association, Fukujuji Hospital, Kiyose, Japan"
      ],
      "name": "Masafumi Shimoda"
    },
    {
      "affiliations": [
        "Department of Respiratory Medicine, Akashi Medical Center, Akashi, Japan"
      ],
      "name": "Hisashi Ohnishi"
    },
    {
      "affiliations": [
        "Division of Respiratory Medicine, Toho University Ohashi Medical Center, Meguro, Japan"
      ],
      "name": "Norio Kodaka"
    },
    {
      "affiliations": [
        "Graduate School of Medicine, Department of Respiratory Medicine, Juntendo University, Bunkyo, Japan"
      ],
      "name": "Motoyasu Kato"
    },
    {
      "affiliations": [
        "Department of Respiratory Medicine, Saitama Medical University Hospital, Saitama, Japan"
      ],
      "name": "Makoto Nagata"
    },
    {
      "affiliations": [
        "Department of Respiratory Medicine & Allergology, Faculty of Medicine, Kindai University, Higashiosaka, Japan"
      ],
      "name": "Hisako Matsumoto"
    },
    {
      "affiliations": [
        "Department of Respiratory Medicine, Kakogawa Central City Hospital, Kakogawa, Japan"
      ],
      "name": "Teruaki Nishiuma"
    },
    {
      "affiliations": [
        "Department of Diagnostic Radiology, Fukujuji Hospital, Kiyose, Japan"
      ],
      "name": "Atsuko Kurosaki"
    },
    {
      "affiliations": [
        "Department of Radiology, St Luke’s International Hospital, Chuo, Japan"
      ],
      "name": "Yasuyuki Kurihara"
    },
    {
      "affiliations": [
        "Department of Pathology, Kanto Rosai Hospital, Yokohama, Japan"
      ],
      "name": "Toshimasa Uekusa"
    },
    {
      "affiliations": [
        "Division of Pulmonary Medicine, Department of Medicine, Jichi Medical University, Shimotsuke, Japan"
      ],
      "name": "Masashi Bando"
    },
    {
      "affiliations": [
        "Department of Respiratory Medicine, Institute of Science Tokyo, Bunkyo-ku, Tokyo, Japan"
      ],
      "name": "Yasunari Miyazaki"
    },
    {
      "affiliations": [
        "Second Division, Department of Internal Medicine, Hamamatsu University School of Medicine, Hamamatsu, Japan"
      ],
      "name": "Takafumi Suda"
    },
    {
      "affiliations": [
        "Department of Respiratory Medicine, Toho University Omori Medical Center, Ota, Japan"
      ],
      "name": "Kazuma Kishi"
    },
    {
      "affiliations": [
        "Department of Respiratory Medicine, Toho University Omori Medical Center, Ota, Japan"
      ],
      "name": "Sakae Homma"
    }
  ],
  "title": "Humidifier lung and summer-type hypersensitivity pneumonitis in Japan: a nationwide retrospective observational study of clinical, radiological and pathological features",
  "uid": "4bcea73f-ab81-500b-b6f2-8993bcdde79b"
}