Further out into the fibrous shell there is a zone that contains T cells and plasma cells in association with blood vessels. The histology of pulmonary nodules are similar to that of subcutaneous nodules, with central necrosis surrounded by palisading macrophages and inflammatory infiltrate. Risk Factors
Rheumatoid nodules develop if a person currently has rheumatoid arthritis. However, not all people with rheumatoid arthritis develop rheumatoid nodules. Some risk factors for rheumatoid nodules for people with rheumatoid arthritis may include:
Smoking (strong association)
Elevated levels of serum rheumatoid factors
HLA-DRB1 gene (weak association)
Trauma to small vessels
Having severe rheumatoid arthritis
Taking Methotrexate over other arthritis drugs

Diagnosis
Differential diagnosis of rheumatoid nodules can be classified from localization, depth pathology, age of onset, persistence, rheumatoid factor, concomitant joint disease, and bone erosions. Diagnosis is typically determined clinically by a rheumatologist. Rheumatoid arthritis associated rheumatoid nodules are typically subcutaneous and occur at extensor sites. The onset typically starts in adulthood and presents with rheumatoid factors and bone erosions, and concomitant joint diseases. The pathology is characterized by central necrosis, palisading mononuclear cells, and perivascular lymphocytic infiltrations.Rheumatoid nodulosis is characterized by multiple subcutaneous nodules presenting with rheumatoid factors but an absence of joint complaints. The nodules are typically small and concentrated on the extensor sites of the hands and feet, sometimes accompanied by bone erosions. The onset typically starts in adulthood with a pathology similar to rheumatoid arthritis associated rheumatoid nodules.Benign rheumatoid nodules are often not associated with rheumatoid factors or concomitant joint diseases. They are typically found on the feet, scalp, and pretibial regions.
A rheumatoid nodule is a lump of tissue, or an area of swelling, that appear on the exterior of the skin usually around the olecranon (tip of the elbow) or the interphalangeal joints (finger knuckles), but can appear in other areas. There are four different types of rheumatoid nodules: subcutaneous rheumatoid nodules, cardiac nodules, pulmonary nodules, and central nervous systems nodules. These nodules occur almost exclusively in association with rheumatoid arthritis. Very rarely do rheumatoid nodules occur as rheumatoid nodulosis (multiple nodules on the hands or other areas) in the absence of rheumatoid arthritis. Rheumatoid nodules can also appear in other areas of the body other than the skin. Less commonly they occur in the lining of the lung or other internal organs. The occurrence of nodules in the lung of miners exposed to silica dust was known as Caplan’s syndrome. Rarely, the nodules occur at diverse sites on body (e.g. upper eyelid, distal region of the soles of the feet, vulva and internally in the gallbladder, lung, heart valves, larynx, and spine).Rheumatoid nodules can vary in size from 2 mm to 5 cm and are usually rather firm to the touch. Quite often they are associated with synovial pockets or bursae. About 5% of people with rheumatoid arthritis have such nodules within two years of disease onset, and the cumulative prevalence is about 20 to 30%. Risk factors of developing rheumatoid nodules include as smoking and trauma to small vessels.In the majority of the time, nodules are not painful or disabling in any way.