Rheumatoid arthritis (RA) is a chronic autoimmune disease known for affecting joints, causing pain, swelling, and stiffness. As a systemic condition, RA can also impact various other organ systems, including the skin, leading to diverse manifestations.
Underlying Mechanisms of Skin Involvement
Systemic inflammation in RA plays a significant role in its skin manifestations. The immune system, which mistakenly attacks the body’s own tissues in RA, releases inflammatory mediators like tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). These circulate, contributing to widespread inflammation that impacts skin health.
Autoantibodies, such as rheumatoid factor and anti-citrullinated protein antibodies (ACPA), also contribute to immune dysregulation. These antibodies can form immune complexes that deposit in skin and blood vessel tissues, triggering localized inflammation and damage, which results in visible skin changes.
Vascular changes also affect the skin. Chronic inflammation can lead to vasculitis, or inflammation of blood vessels. This impairs blood flow to skin areas, causing issues from subtle discoloration to severe tissue damage and ulceration.
Specific Skin Manifestations of Rheumatoid Arthritis
Rheumatoid Nodules
Rheumatoid nodules are among the most recognizable skin manifestations associated with rheumatoid arthritis. These are firm, painless lumps typically forming under the skin, often over bony prominences like elbows, fingers, or the Achilles tendon.
Nodules can also develop in other areas subject to pressure or trauma. While generally benign, their presence often indicates more severe or long-standing RA. Approximately 20% to 30% of individuals with RA develop rheumatoid nodules.
Rheumatoid Vasculitis
Rheumatoid vasculitis involves inflammation of blood vessels, a less common but potentially serious RA complication. Damage to small vessels can lead to palpable purpura, which are small, raised red or purple spots that do not blanch when pressed.
Medium-sized vessel involvement can cause skin ulcers, particularly on the lower legs, which can be slow to heal. Other presentations include livedo reticularis, a net-like, reddish-blue skin discoloration, and digital infarcts, small areas of tissue death on fingertips or toes. Though rare, rheumatoid vasculitis is often associated with severe, active RA and may require intensive treatment.
Other Less Common Skin Conditions
Palmar erythema, a reddening of the palms, can occur in RA. It appears as diffuse redness, often more pronounced on the thenar and hypothenar eminences (fleshy parts at the base of the thumb and little finger). This is thought to relate to the systemic inflammatory state.
Pyoderma gangrenosum is a rare but painful ulcerative skin condition associated with RA. It typically begins as small, red bumps or pustules that rapidly enlarge and break down into deep, painful ulcers with undermined, violaceous borders. These ulcers require aggressive management.
Interstitial granulomatous dermatitis presents as skin-colored to red papules, plaques, or nodules, sometimes arranged in a cord-like pattern, often on the trunk or limbs. It is considered a reactive process linked to systemic inflammatory conditions like RA.
Atrophie blanche refers to white, atrophic (thinned) scars that can develop on the lower legs and ankles. These scars often have a telangiectatic (spider vein) border and are typically associated with chronic venous insufficiency or previous vasculitis, which can occur in RA. They represent areas of skin that healed poorly after injury or inflammation.
Identifying Skin Changes in Rheumatoid Arthritis
Recognizing RA skin manifestations requires a thorough clinical examination by a healthcare professional. A dermatologist or rheumatologist will carefully inspect the skin for characteristic lesions like nodules, rashes, or ulcers. Their appearance, location, and progression provide diagnostic clues.
Diagnostic tools aid in identifying these skin conditions. A skin biopsy, where a small tissue sample is taken for microscopic examination, can confirm diagnoses like vasculitis or granulomatous inflammation. This analysis helps differentiate RA-related skin issues from other dermatological conditions.
Blood tests, while not specific for skin involvement, assess inflammation markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), and detect autoantibodies. These tests support RA diagnosis and indicate disease activity. The presence of skin changes often correlates with more active or severe RA.