Monopolar needle electrode spatial recording characteristics

The recording characteristics of the monopolar needle in three dimensions have not been well established. A simple spherical recording territory is commonly assumed with the very tip proposed to have a greater spatial recording sensitivity by some authors. We demonstrate, by enlarged physical modeling in a homogeneous volume conductor, that the recorded amplitude diminishes more gradually radially away from the conical surface than distally past the tip or proximal to the insulation edge. The sensitivity over the exposed metallic surface is found to be uniformly proportional to the area, which results in relatively less sensitivity at the tip than the middle and proximal portions of the conical recording surface. The overall spatial amplitude recording characteristics can be better described by an apple shape than a sphere, centered at the midportion of the exposed conical surface. A better appreciation of the actual spatial recording characteristics of the monopolar needle electrode can result in more accurate physiologic interpretations of quantitative motor unit analysis. © 1996 John Wiley & Sons,Inc.     

B cell epitope specificity in ANCA‐associated vasculitis: does it matter?

Pauci‐immune idiopathic small‐vessel vasculitis is strongly associated with the presence of antineutrophil cytoplasm autoantibodies (ANCA). Antibodies to PR3 predominate in patients with Wegener's granulomatosis; antibodies to myeloperoxidase (MPO) are found more frequently in patients with microscopic polyangiitis. There is increasing in vivo and in vitro evidence for a pathogenic role of ANCA in systemic vasculitis based on associations of ANCA with disease activity. If ANCA are pathogenic, why is the course of disease different from one patient to another? Antibodies can recognize different binding sites (epitopes) on their corresponding antigens. Differences in binding specificity may influence the pathogenic potential of the antibodies. Differences between epitope specificity of ANCA between patients or changes in epitope specificity of ANCA in time in an individual patient may, accordingly, result in differences in disease expression. This review will focus on epitope specificity of autoantibodies in systemic autoimmune diseases and especially on the epitope specificity of PR3– and MPO–ANCA. We will discuss whether PR3–ANCA or MPO–ANCA recognize different epitopes on PR3 and MPO, respectively, and whether the epitopes recognized by ANCA change in parallel with the disease activity of ANCA‐associated vasculitis. Finally, we will speculate if the direct pathogenic role of ANCA can be ascribed to one relapse‐ or disease‐inducing epitope. Characterization of relapse‐ or disease‐inducing epitopes bound by PR3–ANCA and MPO–ANCA is significant for understanding initiation and reactivation of ANCA‐associated vasculitis. Elucidating a disease‐inducing epitope bound by ANCA may lead to the development of epitope‐specific therapeutic strategies.