Caplan syndrome

A 65-year-old male with a medical history of severe seropositive rheumatoid arthritis (RA) and a cumulative exposure of 40 pack years. The patient is a former construction worker, with repeated occupational exposures to both asbestos and silica. He has no respiratory symptoms, and pulmonary clinical evaluation is normal.

A high-resolution computed tomography (HRCT) of the lungs revealed multiple well-defined lung nodules with an apical and peripheral predilection and relatively spared lung bases (Figures 1 and 2). The nodules exhibited variable diameters ranging from some millimetres to approximately one centimetre and showed sporadic calcifications (Figure 3). In the upper lobes, these nodules showed a tendency to coalesce, without cavitation. There is also mild parastatal emphysema with apical predilection, as well as diffuse bronchial wall thickening.

Background

Caplan syndrome, also termed rheumatoid pneumoconiosis, manifests as the development of lung nodules in individuals with seropositive RA and a history of exposure to inhaled inorganic dust particles, predominantly coal and silica. Histologically akin to rheumatoid nodules, these lung nodules, or Caplan nodules, also exhibit concentric rings of dust particles and an outer zone of active inflammation. It is a rare disease with a reported incidence of 1 in every 100,000 people, with a decline in incidence due to further decrease in exposure to coal, asbestos and silica [1].

Clinical Perspective

Caplan syndrome usually manifests with cough and shortness of breath alongside rheumatoid arthritis symptoms like inflammatory joint pain and morning stiffness. However, symptoms are often non-specific or absent, as in our case. Onset typically occurs suddenly, with subsequent disease varying from complete regression to further progression [1]. Physical examination typically shows tender, swollen metacarpophalangeal joints and rheumatoid nodules. Chest auscultation may detect persistent diffuse crackles.

Imaging Perspective

On imaging, these Caplan nodules present as multiple lung nodules ranging from approximately 5 millimetres to several centimetres, which are distributed throughout the lungs, with a predilection for peripheral zones and upper lobes. Often clustered in crops, these nodules may merge to form larger, confluent masses, and occasionally cavitate or calcify. They may become coalescent as in progressive massive fibrosis (PMF), but do not express the associated scarring, retraction or central migration characteristic of PMF. Solitary cavitating lung nodules may mimic cancer or infection radiologically, especially upon growth. Furthermore, rheumatoid nodules in individuals with pneumoconiosis may resemble silicosis nodules, often necessitating correlation with clinical history, symptoms, and histological examination for accurate diagnosis [1,2].

Outcome

Management of RA should adhere to current guidelines, regardless of the presence of Caplan syndrome [1]. The Caplan nodules necessitate treatment upon complication, such as rupture. In our case, no treatment was initiated because of the newly discovered pulmonary manifestations.

Take Home Message / Teaching Points

Caplan syndrome, the combination of seropositive rheumatoid arthritis and pneumoconiosis, is an important differential diagnosis in patients with RA, a history of exposure to inhaled inorganic dust particles and multiple lung nodules.

All patient data have been completely anonymised throughout the entire manuscript and related files.