Introduction:
Pulmonary involvement is a frequent and prognostically significant extra-articular manifestation of rheumatoid arthritis (RA). Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) is the most common respiratory presentation and a major contributor to morbidity and mortality. Growing evidence suggests the lungs may be a site for initiating autoimmune processes preceding clinically overt RA.

Case description:
A 54-year-old female with a 14-year history of idiopathic pulmonary arterial hypertension (iPAH) presented with an acute onset of polyarthritis following an emotional stress accompanied by infection. She exhibited high disease activity (DAS28: 6.74), significant systemic inflammation (erythrocyte sedimentation rate: 96 mm/h, C-reactive protein: 105 mg/l), and high titers of autoantibodies (rheumatoid factor: 58.44 IU/ml, anti-citrullinated protein antibodies: > 500 U/ml). High-resolution computed tomography (HRCT) and lung cryobiopsy confirmed an organising pneumonia (OP) pattern (Fig. 1). Pulmonary function tests showed forced vital capacity 88% and reduced diffusion capacity of the lungs for carbon monoxide 58%.Based on clinical, serological, and radiological findings, a diagnosis of RA-ILD was established. Treatment was initiated with intravenous methylprednisolone, followed by a regimen of methotrexate, hydroxychloroquine and tapering dose of oral methylprednisolone.

Conclusions:
This case highlights the diagnostic challenges of RA with pulmonary involvement. The patient’s ILD, characterised by an inflammatory OP pattern on HRCT, was preceded by long-standing iPAH. This clinical sequence suggests a possible gradual evolution from a subclinical pulmonary state, such as interstitial pneumonia with autoimmune features, to clinically defined RA. Early recognition of RA-ILD, enabling timely immunomodulatory and immunosuppressive treatment, is crucial for influencing the disease course and prognosis, particularly in patients with long-standing unexplained pulmonary disease.