Systemic Lupus Erythematosus (Lupus) and Rheumatoid Arthritis (RA) are chronic autoimmune diseases where the immune system mistakenly targets the body’s healthy tissues. Lupus is a systemic condition that can cause inflammation in almost any organ system, including the skin, joints, kidneys, and brain. Rheumatoid Arthritis, by contrast, primarily focuses its inflammatory attack on the lining of the joints, known as the synovium. This shared immune system dysfunction leads to similar symptoms, such as joint pain and fatigue, but the overall presentation and progression of each disease are distinct.
Understanding Co-Occurrence and Overlap Syndromes
An individual can develop both Systemic Lupus Erythematosus and Rheumatoid Arthritis, meeting the established diagnostic criteria for each disease. This simultaneous presence is rare, but when it occurs, it is sometimes referred to as Rhupus syndrome. This designation describes a true co-occurrence where a patient exhibits the specific clinical and laboratory markers necessary to confirm both RA and SLE diagnoses.
The concept of an overlap syndrome is slightly different from a full co-occurrence. An overlap syndrome describes a scenario where a patient presents with features of multiple connective tissue diseases, but does not fully satisfy the classification criteria for any single one. Rhupus is considered a specific type of overlap syndrome, though some rheumatologists debate whether it is a unique entity or simply an erosive form of Lupus arthritis. The prevalence of this simultaneous presentation is low, occurring in approximately 0.09% to 2% of patients with systemic rheumatic diseases.
Key Differences in Clinical Presentation
While both conditions cause joint pain, the pattern and nature of the arthritis often differ, guiding diagnosis. Rheumatoid Arthritis typically involves a symmetrical pattern of inflammation in the smaller joints, such as the hands and feet. A hallmark of RA is destructive arthritis, where chronic inflammation leads to progressive erosion of the bone and cartilage within the joint capsule.
Joint stiffness associated with RA is often most pronounced in the morning and can last for 30 minutes or more. Lupus arthritis, in contrast, is frequently non-erosive, causing pain and swelling but rarely resulting in permanent joint damage or deformity. If deformity occurs in Lupus, it is often a reversible condition known as Jaccoud arthropathy, which is less disabling than the joint destruction seen in RA.
Beyond the joints, the systemic features of Lupus set it apart from RA. Lupus frequently involves major organs, with inflammation of the kidneys (nephritis) being a common and serious manifestation. Skin involvement is also characteristic, including the distinct butterfly-shaped malar rash across the cheeks and nose, and heightened sensitivity to sunlight (photosensitivity). While RA can involve organs like the lungs and heart, it is less likely to affect the kidneys or present with characteristic rashes.
Diagnostic Confirmation of Dual Conditions
Confirming the presence of both Lupus and Rheumatoid Arthritis requires laboratory testing and advanced imaging. Blood tests search for specific autoantibodies characteristic of each disease. For Lupus, the presence of antinuclear antibodies (ANA) is common, but more specific markers include anti-double-stranded DNA (anti-dsDNA) and anti-Smith (anti-Sm) antibodies.
In contrast, the diagnosis of RA is heavily supported by the presence of Rheumatoid Factor (RF) and antibodies against cyclic citrullinated peptide (anti-CCP). Anti-CCP antibodies are considered highly specific for RA and are particularly associated with erosive joint damage. General inflammatory markers and complement proteins can also differentiate the two conditions.
During Lupus flares, levels of complement proteins C3 and C4 are often low, while the C-reactive protein (CRP) level may remain relatively normal. In active RA, however, the CRP level is typically elevated, a pattern that helps distinguish the primary driver of inflammation. Imaging studies, such as X-rays or magnetic resonance imaging (MRI), are also used to look for the characteristic bone erosions that are a definitive sign of chronic RA.
Managing Combined Autoimmune Disease
Treating a patient with both Lupus and Rheumatoid Arthritis presents a therapeutic challenge, as the strategy must address the most aggressive symptoms of both conditions. The initial approach often involves using a conventional disease-modifying antirheumatic drug (DMARD) like methotrexate, which manages joint inflammation and helps prevent the bone damage characteristic of RA. Hydroxychloroquine, an antimalarial drug, is also a standard component of Lupus treatment, continued for its ability to reduce flares and organ damage.
If joint inflammation remains active, a biologic therapy may be introduced to target specific inflammatory pathways for the RA component. The systemic and organ-specific inflammation of Lupus often requires the addition of immunosuppressants, such as azathioprine, to control disease activity and protect organs like the kidneys. Glucocorticoids, or steroids, are frequently necessary during severe disease flares in both conditions. Close, ongoing monitoring by a rheumatologist is required to balance the medications, minimize side effects, and adjust the treatment plan.