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Caplan’s syndrome is the association of pneumoconiosis (commonly Coal Workers’ Pneumoconiosis or silicosis) with rheumatoid arthritis (RA), characterized by the presence of multiple, well-defined pulmonary nodules that may cavitate.

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First described by Anthony Caplan in 1953 among coal miners with RA.

https://www.youtube.com/watch?v=kU43RBNOD_s

Etiopathogenesis

Underlying mechanism: autoimmune + dust exposure.
Inhaled dust particles (coal, silica) stimulate lung macrophages and fibrotic response.
In RA patients, immune complex deposition and chronic inflammation amplify the fibrotic reaction.
Leads to development of necrotizing rheumatoid nodules in lung parenchyma.
Nodules can appear even if pneumoconiosis is radiologically mild.

Rheumatoid Pneumoconiosis (Caplan’s Syndrome).jpg

Clinical Features

Typically occurs in RA patients with occupational dust exposure (coal, silica).
May be asymptomatic (incidental finding).
Symptoms: cough, dyspnea, pleuritic pain, hemoptysis (if cavitation/rupture).
May present with systemic RA symptoms: joint pain, morning stiffness, rheumatoid nodules elsewhere.

Radiology

Modality	Imaging features
XR	• Multiple, well-defined, rounded nodules, usually 0.5–5 cm in size.
• Distribution: peripheral and upper lobes.
• Background of simple pneumoconiosis (small nodules).
• Cavitation may occur (especially if secondary infection/TB).
• Nodules may wax and wane in size (unique feature).
HRCT	• Multiple, well-circumscribed nodules, sometimes with cavitation.
• Peripheral and upper-lung predominant.
• Surrounding emphysema may be present.
• Nodules often appear rapidly (within months) compared to typical pneumoconiosis nodules.