Are the cut-offs of the rheumatoid factor and anti-cyclic citrullinated peptide antibody different to distinguish rheumatoid arthritis from their primary differential diagnoses?

OBJECTIVE: Rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibody (anti-CCP) are commonly used for diagnosis of rheumatoid arthritis (RA), although other rheumatic diseases with arthritis can test positive. This study aimed to determine the cutoff values for RF and anti-CCP with the best diagnostic performance in a sample of patients with RA, compared with other rheumatic diseases. METHODS: This was a descriptive, prospective study. EUROINMMUN enzyme-linked immunosorbent assays for RF isotypes immunoglobulin (Ig) A (IgA), IgG and IgM and third-generation assay IgG for anti-CCP were used in serum samples of patients with RA, other rheumatic diseases and healthy subjects. The cutoff with the best diagnostic performance was determined by the Youden Index and receiver operating characteristic analysis Results: Three hundred and thirty-two serum samples were analysed. The cutoffs proposed in our population were for RF in RA patients versus other rheumatic diseases, and healthy subjects IgM 135 IU/mL, for each disease, compared with RA, were psoriatic arthritis (Psa) IgA 47.2 IU/mL, clinically suspicious arthralgia (CSA) IgA 39.5 IU/mL, primary Sjögren's syndrome (pSS) IgM 180.6 IU/mL, systemic lupus erythematosus (SLE) IgA 42.6 IU/mL, primary fibromyalgia (pFM) IgM 68.6 IU/mL, osteoarthritis (OA) IgM 48 IU/mL, gout IgM 117 IU/mL and healthy IgM 16.3 IU/mL. For anti-CCP, in RA patients versus other rheumatic diseases, and healthy subjects 6.95 IU/mL, for each disease, compared with RA, were Psa 6.8 IU/mL, CSA 9.95 IU/mL, pSS 20.7 IU/mL, SLE 6 IU /mL, pFM 11.8 IU/mL, OA 11.9 IU/mL, gout 5 IU/mL and healthy 5 IU/mL. CONCLUSION: Irrespective of the manufacturer's suggested cutoff, the RA versus differential diagnosis cutoffs must be considered.

Low-dose rituximab therapy in steroid-refractory thrombocytopenia due to systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is an autoimmune disease, characterized by multi-organ symptomatology. 16% of the patients with autoimmune thrombocytopenia have SLE and are associated with high mortality. Intravenous methylprednisolone or high-dose steroids are the first-line treatments in those patients who experienced life-threatening bleeding or have a severely low platelet count, whereas a second line includes splenectomy, as well as other immunosuppressive agents as monotherapy or combined therapy, including azathioprine, cyclophosphamide, cyclosporine, and mycophenolate mofetil. However, response rates of these therapies vary considerably. Rituximab (RTX) became a useful tool in the treatment of autoimmune diseases, due to the decrease of autoantibodies production. In addition, there is evidence that low doses of RTX (100 mg IV per week for 4 weeks) can have a similar effect compared to the standard dose. The objective of this study was to describe the response to low doses of RTX in patients with lupus-induced thrombocytopenia. We present a report of four female patients with newly diagnosed SLE, accompanied by purpuric syndrome and severe thrombocytopenia (< 30 × 109/L) as the clinical debut that was refractory to glucocorticoids (GC) therapy and treated with low doses of RTX. By week 5, complete response (> 100 × 109/L) was achieved in two patients, partial response (> 50 × 109/L) in 1 patient, and no response in one patient. There is little information on the treatment of SLE-associated autoimmune thrombocytopenia. The most extensive study found at the time of our search was the study of 10 Asian patients. They found that 80% of the patients responded by week four and maintained until week 24 of follow-up. At week 36, a follow-up for two patients showed relapse; this occurred on patients with the most disease duration (> 5 years) and was associated with a lower response rate. In contrast, our study with four patients found that half of them presented a complete response: one patient added concomitant therapy with azathioprine (AZA) and another patient without the concomitant therapy. A third patient with a partial improvement, this was seen by week five of treatment. Moreover, a fourth patient who did not have a response by week five of treatment presented a clinical response in subsequent appointments with a count of > 100 at week 24. Those patients who required concomitant use of AZA were patients who had positive antiphospholipid serology. The use of low-dose RTX for the management of severe thrombocytopenia refractory to GC in patients with SLE has a good response. It could be a safe, economical, and effective therapy.