Respiratory decline in adult patients with Becker muscular dystrophy: A longitudinal study.

Becker muscular dystrophy (BMD) is a rare hereditary neuromuscular disease, caused by a genetic defect in the Duchenne Muscular Dystrophy (DMD) gene. We studied the natural history of respiratory function and its affecting factors in 23 adult BMD patients. These important data are needed for (future) clinical trials in BMD but are largely lacking. Patients had a median age of 51 years (28-78y) and median follow-up duration of 14 years (2-25y). We analysed 190 pulmonary function measurements with a median interval of one year (1-17y) and measured a 1.00% decline of Forced Vital Capacity percent predicted (FVC%pred) per year (p = 0.004). Loss of ambulation significantly increased the annual rate of FVC decline and was dependent of patient's body mass index (BMI; p = 0.015), with increases in BMI correlating with an even more rapid deterioration of FVC. A decline in Medical Research Council (MRC) sum score was significantly correlated with a decline in FVC (p = 0.003). We conclude that adult BMD patients experience a significant but mild respiratory decline. However, this decline is significantly more rapid and clinically relevant after loss of ambulation, which warrants a more vigilant follow-up of respiratory function in this subgroup.

Anti-streptavidin IgG antibody interference in anti-cyclic citrullinated peptide (CCP) IgG antibody assays is a rare but important cause of false-positive anti-CCP results.

BACKGROUND: The detection of anti-cyclic citrullinated peptide (anti-CCP) IgG antibodies in blood is mainly used for the diagnosis of rheumatoid arthritis. Falsely elevated anti-CCP IgG antibodies due to anti-streptavidin IgG antibodies were suspected in our laboratory. METHODS: In this study, we evaluated, in a standardized approach, the prevalence of anti-streptavidin IgG antibodies in a primary care setting and the effect of anti-streptavidin IgG antibodies on anti-CCP IgG assays from three different important commercial manufacturers (Abbott, Roche Diagnostics, Thermo Fisher Scientific). Three different populations were consecutively and prospectively studied: serum samples from 1000 ambulatory patients, 286 serum samples from patients for which anti-CCP was requested and 89 serum samples from patients which had previously given a positive anti-CCP result on Architect® i2000. RESULTS: The frequency of confirmed anti-streptavidin IgG-positive samples detected in this study was 0.6% (8/1375). Anti-CCP IgG was determined on the eight samples with confirmed anti-streptavidin IgG antibodies: with the Cobas® method, seven positive anti-CCP results were observed and five positive anti-CCP results with the Architect® method. No positive anti-CCP IgG results were obtained with the EliA™ method. Rheumatoid factor was negative in these eight samples. CONCLUSIONS: Anti-streptavidin IgG antibodies rarely cause false-positive results in some anti-CCP assays. However, despite being an infrequent assay problem, it could possibly lead to diagnostic confusion or even an incorrect diagnosis of rheumatoid arthritis.

Elimination of complement interference can improve the diagnostic performance of the VIDAS CMV IgG assay in acute cytomegalovirus infections.

In this study we showed that complement factors are responsible for assay interference in the VIDAS cytomegalovirus (CMV) immunoglobulin G (IgG) assay. Three different serum treatments were applied to show the cause of interference: heat treatment (56 °C), adding cobra venom factor, and adding EDTA. Elimination of complement interference by EDTA treatment of serum was prospectively evaluated on 215 CMV IgM positive samples and a sensitivity increase of the VIDAS CMV IgG assay was noticed. On average the CMV IgG level increased 100% after EDTA treatment of the serum. In paired serum samples from 38 patients we could show that serum treatment with EDTA can make the CMV IgG level changes more obvious in recent CMV infections. Since the CMV IgG avidity II assay on VIDAS depends on the determination of CMV IgG, the CMV IgG avidity was also evaluated in this study but only a limited effect of the complement interference was observed.