Rheumatoid Nodule

Definition

Clinical Features

• In ≈20% of patients with rheumatoid arthritis1
• Rarely in systemic lupus erythematosus2–4
• Location:
  • usually vicinity of joints
  • primarily subcutaneous tissue
  • may involve deep and even superficial dermis
• Usually persist months to years

Pathogenesis

• Probably vasculitic5

Gross Pathology

• Fibrous white mass:
  • mm to cm in size
  • creamy yellow irregular areas of necrobiosis:
    • may be clefts and cystic spaces in old lesions

Histopathology

• Areas of necrobiosis (Figs 1 and 2
  

  Fig. 1: Rheumatoid nodule. (H&E)

  

  Fig. 2: Rheumatoid nodule. A palisade of elongate histiocytes surrounds a zone of ‘necrobiosis'. (H&E)

  ):
  • irregular
  • one or more
  • in subcutis and dermis
  • surrounded by:
    • well-developed palisade of elongated histiocytes
    • occasional lymphocytes, neutrophils, mast cells and foreign body giant cells6
  • center of necrobiotic focus:
    • usually:
      • homogeneous
      • eosinophilic7
    • sometimes contains necrotic blood vessel associated with nuclear fragments or sparse neutrophils
    • fibrin8
• Old rheumatoid nodules:
  • may be:
    • dense fibrosis
    • clefts
    • ‘cystic’ degeneration of necrobiotic foci
• Dermis and subcutis surrounding necrobiotic granulomas:
  • perivascular round cell infiltrate:
    • includes plasma cells
    • may be eosinophils
  • Uncommonly, acute vasculitis in surrounding vessels
  • Occasional superficial nodule may perforate epidermis9

Diagnosis

• Accelerated rheumatoid nodulosis:
  • development of multiple small nodules on hands, feet and ears during methotrexate therapy10

Differential Diagnosis

• Subcutaneous or deep variant of granuloma annulare:
  • areas of necrobiosis often pale and mucinous with tendency to basophilia:
    • unusual to find mucin in necrobiotic foci in rheumatoid nodules7