Rheumatoid arthritis (RA) is a chronic autoimmune disorder that primarily targets the lining of the joints, causing inflammation and pain. Beyond the joints, the disease can manifest in other areas of the body, known as extra-articular involvement. Rheumatoid nodules are the most common of these signs, appearing as lumps that form just beneath the skin’s surface in many patients. These growths are a physical manifestation of the underlying inflammatory process associated with RA.
Visual and Physical Description
Rheumatoid nodules typically present as firm, rounded, or oval lumps located under the skin, known as subcutaneous nodules. Their size varies considerably, ranging from small, pea-sized formations to larger growths comparable to a walnut or small lemon. The overlying skin usually appears normal in color, or sometimes slightly reddish if irritated.
The texture of the nodules is often described as firm and rubbery, feeling much like a small pebble or marble beneath the skin. While they are generally non-tender, they can become painful if located near a nerve, infected, or if the overlying skin develops an ulceration. Some nodules are mobile, moving slightly under the skin, while others are fixed firmly to underlying structures like tendons, bone coverings, or fascia.
These formations are collections of inflammatory tissue and can sometimes feel doughy rather than hard. They may emerge as a single lump or appear in clusters, sometimes growing larger over time, or shrinking and disappearing spontaneously. Multiple, small nodules, often around 0.5 centimeters, are sometimes referred to as micronodules.
Typical Locations of Nodule Formation
Rheumatoid nodules most frequently develop over bony prominences or areas subjected to repeated mechanical pressure, friction, or minor trauma. This mechanical stress irritates the tissue, promoting nodule formation. The most common site is the extensor surface of the forearms, particularly near the elbow joint.
Other frequent locations include the fingers and knuckles, the Achilles tendon near the heel, and the sacrum or hips. In bedridden patients or those with limited mobility, nodules can form over other pressure points, such as the back of the head or the tailbone. Less commonly, they occur in the sclera, the vocal cords, or within internal organs.
Underlying Cause and Medical Significance
The formation of a rheumatoid nodule is a complex immunological process that begins deep within the tissue. Internally, the nodule has a characteristic structure known as a palisading granuloma. This structure consists of a central area of dead tissue, primarily made up of fibrin and collagen, surrounded by a ring of inflammatory cells.
This ring is composed of palisading macrophages and fibroblasts, which are immune and connective tissue cells arranged in a fence-like pattern. The presence of these nodules is associated with a more severe form of RA. They almost exclusively occur in patients who test positive for inflammatory markers, such as rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) antibodies.
Nodules that form in internal organs, such as the lungs or heart, are less common but represent a significant extra-articular feature. Pulmonary nodules are often asymptomatic and found incidentally, but they require careful monitoring to distinguish them from other conditions. The presence of rheumatoid nodules signals that the body’s autoimmune response is active outside of the primary joint structures.
Monitoring and Treatment Approaches
The primary approach to managing rheumatoid nodules is controlling the underlying systemic rheumatoid arthritis. Effective RA treatment, typically involving disease-modifying antirheumatic drugs (DMARDs) and biologic therapies, often leads to the shrinking or disappearance of the nodules. Newer therapies have been observed to reduce the incidence of nodule formation.
Patients should monitor existing nodules for signs of complication, such as rapid growth, pain, warmth, redness, or skin breakdown, which could indicate infection or ulceration. If a nodule is bothersome, a localized corticosteroid injection may be used to reduce its size and inflammation. This local treatment can provide relief for isolated lumps.
Surgical removal of a nodule is generally avoided because it carries a risk of recurrence at the same site and can lead to poor wound healing. Surgery is typically reserved for cases where a nodule causes severe functional impairment, presses on a nerve, becomes persistently infected, or leads to significant erosion of the overlying skin. Treating the systemic disease remains the most effective long-term strategy for nodule management.