Figure 1.

(A) CSF IgG passively diffused from blood to CSF in normal population. Plot of CSF/serum quotients with hyperbolic function of quotient ratios (“Reibergram”). Reference range defined by Q_{L im} = Q _mean ± 2SD or ±3SD involving 96% and 99% of normal population, respectively. Dotted line is upper normal limit (>0.7) of IgG index, intersecting Q_{L im} curve at two points. Right insert: probability curve of basal Q_{I gG} for a given Q_{A lb}. The maximum probability is obtained for Q_mean. Points are obtained from a simulated healthy population. (B). Range of calculated intrathecal IgG synthesis depending on basal Q_{I gG} estimation. True IgG_{L oc} should be calculated based on normal Q_{I gG_basal} preceding disease onset (gray circle), which is unknown. In practice, Q_{I gG_Loc}, and therefore, IgG_{L oc,} strongly depend on choice of possible Q_{I gG_basal}. By raising point B as a definitely abnormal Q_{I gG} (≫Q_{L im}), the range for the ratio of intrathecally synthesized IgG depends on estimation of basal (before disease onset) Q_{I gG_basal}. In individual patients, Q_{L im}(+3SD) (point A’) is usually used as an approximation of basal Q_{I gG_basal}. However, the true Q_{I gG_basal} may be anywhere on the segment A’ – A’’, with the highest probability closest to Q _mean at point A. Therefore, quantitative estimation of IgG synthesis IgG_{L oc}=(Q_{I gG} – Q_{I gG_basal}) x [IgGserum] is strongly influenced by arbitrary choice of Q_{I gG_basal}. (C) IgG_{L oc} depending on basal Q_{I gG} estimation. IgG_{L oc(}Lim3SD)= 20 mg/L, IgG_{L oc}(mean) ≈ 43 mg/L. Therefore, the true IgG_{L oc} of Q_{I gG}(B) is in the range of 20–65 mg/L. Using point B at Q_{I gG}=Q_{L im}(3SD) + 2 and [IgGserum] = 10 g/L. (D) Error range of IgG_{L oc} calculations assuming various R ratios (R=Q_{I gG_norm}/Q_{I gG_basal}). A ratio of 1.5 is equal to Q_{L im}3SD/Q _mean. Calculations assume that [IgGserum] = 10 g/L and Q_{I gG_basal} = Q _mean.