Table 4.

Differential diagnosis of HD-ILDs

Variable	HD-ILD	Acute interstitial pneumonitis	Hypersensitivity pneumonitis [45]
Cause	Toxic chemicals in HD	No identified causes	Recurrent exposure to causative environmental
Clinical feature	Subacute cough and dyspnea followed by rapidly progressing respiratory difficulty	Rapid onset with a prodromal illness for 7− 14 days before presentation	Fever, dry cough, and dyspnea after exposure to causative agents
Radiologic feature	Early: patchy consolidation, mainly in the lower lung	Diffuse, bilateral, air-space opacification	Upper- and middle-lobe predominant groundglass opacities, poorly defined centrilobular nodules; mosaic attenuation, air trapping, or rarely, consolidation
	Late: centrilobular opacity
	Resolving phase: faint centrilobular nodules
	Commonly combined air leak syndrome
Pathologic feature	Early: bronchiolar destruction, with alveolar destruction	Diffuse alveolar damage	Lymphoplasmocytic/mononuclear (macrophage) infiltrates, airway-centric lymphocytic infiltrates
	Late: displaced parenchymal architecture due to inflammation and fibrosis, especially in the centrilobular area
Treatment	No identified treatment strategies	Supportive care	Exposure avoidance
Prognosis	High mortality rate (43.8%–58%)	High mortality (more than 50 %)	Variable depends on causal antigen, duration of antigen exposure, and host response

HD, humidifier disinfectants; HD-ILD, humidifier disinfectant-associated interstitial lung diseases.