Is there an association between rheumatoid arthritis and systemic lupus erythematosus (lupus)? Can someone have both diseases or must he or she be diagnosed with only one? What are the challenges in addressing these questions and more?

From a recent article published in the journal Arthritis Research & Therapy, the average RA patient has 1.6 comorbidities and that number increases with the patient's age.  There is increasing interest in the field of comorbidity (the existence of more than one disease in a person, usually independently of one another) and rheumatic diseases.

“The past decade has also brought new insights regarding the comorbidity associated with rheumatic diseases. Strong evidence now shows that persons with RA are at a high risk for developing several comorbid disorders, that these conditions may have atypical features and thus may be difficult to diagnose, and that persons with RA experience poorer outcomes after comorbidity compared with the general population. Taken together, these findings underscore the complexity of the rheumatic diseases and highlight the key role of epidemiological research in understanding these intriguing conditions.”

How are RA and Lupus diagnosed?

The American College of Rheumatology has defined criteria for the diagnosis of rheumatic diseases, including rheumatoid arthritis and lupus.  The following lists of criteria were developed in 1987 (for RA) and 1982 (for lupus).

Rheumatoid Arthritis - At least four of seven criteria must be met for diagnosis:

* Morning stiffness of >1 hour most mornings for at least 6 weeks.
* Arthritis and soft-tissue swelling of >3 of 14 joints/joint groups, present for at least 6 weeks
* Arthritis of hand joints, present for at least 6 weeks
* Symmetric arthritis, present for at least 6 weeks
* Subcutaneous nodules in specific places
* Rheumatoid factor at a level above the 95th percentile
* Radiological changes suggestive of joint erosion

Lupus - At least four of eleven criteria must be met for diagnosis:

* Malar rash: butterfly-shaped rash across cheeks and nose
* Discoid (skin) rash: raised red rashes that scar
* Photosensitivity: skin rash as a result of reaction to sunlight
* Mouth or nose ulcers: usually painless
* Nonerosive Arthritis (bones around joints do not get destroyed): in 2 or more joints with tenderness, swelling, or effusion
* Cardio-pulmonary involvement: inflammation of the lining around the heart (pericarditis) and/or lungs (pleuritis)
* Renal (kidney) disorder: excessive protein in the urine (proteinuria), or cellular casts in the urine
* Seizures or other neurologic disorder
* Hematologic (blood) disorder: low red blood cell count (hemolytic anemia), lower white blood cell count (leukopenia), or low platelet count (thrombocytopenia)
* Immunologic disorder: antibodies to doubled stranded DNA, antibodies to Sm, positive antiphospholipid antibody such as anticardiolipin, or false positive syphillis test (VDRL)