When corticosteroids fail in nonfibrotic hypersensitivity pneumonitis: what comes next?

This protocol addresses Bird fancier's lung presenting as nonfibrotic hypersensitivity pneumonitis — where ground glass opacities are seen on HRCT and BAL shows lymphocytosis, but there is no radiological or histopathological pulmonary fibrosis — in patients who have not adequately responded to a prior course of systemic corticosteroids.

Clinical scenario

International diagnostic guidelines classify hypersensitivity pneumonitis into fibrotic and nonfibrotic phenotypes, recognising that pulmonary fibrosis carries distinct prognostic and treatment implications. The nonfibrotic phenotype is defined by the absence of fibrosis on radiology and pathology, with inflammatory features — ground glass opacities on HRCT and BAL lymphocytosis — as the dominant findings.

Prior treatment — goals not achieved

The previous step used moderate-to-high dose systemic (oral) corticosteroids, with pulsed-dose intravenous methylprednisolone induction for rapid onset or severe physiologic compromise. The target was improvement or stabilisation in clinical symptoms and lung function, assessed between 6 and 12 weeks. When those goals are not met, escalation to a next-line approach is indicated.

Next-line approach (partial overview)

The next step adds a steroid-sparing immunosuppressive agent to the regimen. The goal is improvement or stabilisation of lung function — specifically DLCO and FVC. The full selection criteria, agent choice, and sequencing are detailed in the structured protocol.

Instant Access to Structured Evidence-Based Regimens

References

DOI: 10.1111/resp.14847

Recently published international diagnostic guidelines recommend HP classification into fibrotic or nonfibrotic phenotypes based on the presence or absence of radiological and/or histopathological fibrosis, supported by the observation that pulmonary fibrosis conveys important prognostic and treatment implications.

Moderate-to-high dose systemic corticosteroids would usually be considered for HP patients with features of inflammation (e.g., GGO on HRCT, BAL lymphocytosis, well-documented exposure with acute or sub-acute symptom onset).

A steroid-sparing agent (e.g., mycophenolate mofetil (MMF), azathioprine, cyclophosphamide, rituximab) may enable weaning of corticosteroids and maintenance of therapeutic benefit.

Second-line immunosuppressive agents (MMF, azathioprine, methotrexate) have not been compared head-to-head, and so the choice of agent is often guided by potential side effects and clinician experience.

Several retrospective studies demonstrate a statistically significant improvement in DLCO or FVC following treatment with either MMF or azathioprine.

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