rheumatoid nodule

Etiology

• rheumatoid arthritis (seropositive)
  • methotrexate may increase risk of rheumatoid nodules
• Caplan's syndrome

Pathology

• subcutaneous nodules over extensor surfaces & juxta-articular regions in ~1/3 of patients with rheumatoid arthritis
• they also occur in the lungs, heart, kidney & dura mater
• they are a manifestation of active disease

Microscopic pathology

• angiocentric structure forming around the nidus of agranulomatous arteritis
• central area of fibrinoid necrosis encircled by palisading fibroblasts & mononuclear phagocytes
• perivascular chronic inflammatory infiltrate
• collagenous capsule

Clinical manifestations

• firm, mobile, asymptomatic subcutaneous nodules found over extensor joints & juxta-articular regions
  • elbows, fingers, or forearms
• occur in ~1/3 of patients with rheumotoid arthritis
• may be asymptomatic or painful

* images

Laboratory

• occur almost exclusively in patients with rheumatoid factor

Complications

• breakdown of the skin over rheumatoid nodules
• ulceration & infection
• spread of infection to local bursae, bone or hematogenous spread to distant joints
• accelerated nodulosis
  • treatment with methotrexate or azathioprine increases frequency of rheumatoid nodules & may lead to the occurrence of nodules at unusual places such as fingertip pads

Differential diagnosis

• gouty tophus
• tendon xanthoma
• fibroma
• subcutaneous granuloma annulare
• malignancy, including metastatic lesions

More general terms

• abnormal morphologic structure (malformation)

Additional terms

• Caplan's syndrome
• rheumatoid arthritis (RA)