Diagnosis and Treatment of Hypersensitivity Pneumonitis: S2k Guideline of the German Respiratory Society and the German Society for Allergology and Clinical Immunology

German recommendations for the diagnosis of hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, were last published in 2007. The current S2k Guideline for the Diagnosis and Treatment of Hypersensitivity Pneumonitis replaces these diagnostic recommendations. They were supplemented by the aspect of chronic, and in particular of the chronic fibrotic phenotype of HP, and also, as the first HP guideline, include treatment recommendations. Based on current scientific evidence and on expert opinion, 12 consensus recommendations were developed. They include important statements summarizing the diagnostic process, the treatment indication and therapeutic strategies for patients with HP. Particular emphasis was placed on the different clinical courses (acute and chronic) and their characteristics (inflammatory and/or fibrotic pattern), which present differential diagnostic challenges and ultimately result in different treatment approaches. In addition to general information (diagnosis, classification, clinical disease course, epidemiology, pathogenesis, risk factors, prognosis, and special aspects associated with occupational disease), the guideline will present the various clinical disease entities of HP, some in detail, others in tabular form. A major focus is on the various diagnostic steps and the different treatment approaches. The background information serves to provide a deeper understanding and inform the implementation of the recommendations. In particular, other current international guidelines for the diagnosis of HP as well as German guidelines for the diagnosis of interstitial lung diseases (ILDs) (Leitlinien zur Diagnostik interstitieller Lungenerkrankungen) in general and for the pharmacotherapy of fibrotic ILDs were integrated and considered in this guideline.