"Randomized Controlled Trial Testing the Efficacy of Corticosteroid Therapy Versus Placebo in Fibrotic Hypersensitivity Pneumonitis"

Inclusion Criteria: * Patient aged above 18 years and under 90 years old * Diagnosis of fibrotic HP ("definite" or "high confidence") after MDD according to the criteria proposed by guidelines \[5\] * Fibrosis extent ≥ 10% on chest HRCT * Mild to moderate functional impairment defined by FVC ≥ 50% pred and DLco ≥ 30% pred * Written informed consent for participation in study * Patient affiliated to a social security scheme or CMU beneficiary * Effective contraception for men and woman of childbearing age. Exclusion Criteria: * Uncertain diagnosis of fibrotic HP ("low confidence" or "unlikely") after MDD according to the criteria proposed by guidelines \[5\]. * Severe functional impairment defined by FVC \< 50% pred and DLco \< 30% pred. * Patient previously treated or currently being treated for fibrotic HP (with corticosteroids, any immunosuppressive agent, or anti- fibrotic therapies). * Person under guardianship/ curatorship (sous tutelle/curatelle) * Contraindication to corticosteroid therapy (hypersensitivity to the active substances or to one of the excipients, severe infections, psychotic states not controlled by treatment, live vaccines, uncontrolled diabetes mellitus and uncontrolled arterial hypertension.) or to auxiliary medicinal products * Patient deprived of liberty under judicial or administrative decision * Patient participating in another clinical trial with an investigational medicinal product. The patient may participate in another clinical trial after t…