Background The analysis of cerebrospinal fluid (CSF) is usually done under
steady-state conditions, when proteins (e.g., immunoglobulins) reach diffusion
equilibrium between blood and CSF. However, little data has been published on
CSF analysis under non-steady-state conditions after therapeutic apheresis. By
reducing serum proteins (e.g., immunoglobulins), while leaving CSF unchanged,
therapeutic apheresis might cause spuriously altered intrathecal
immunoglobulin fractions. Methods Based on the incidental finding of plasma
exchange-induced increased intrathecal immunoglobulin fractions in a cohort of
12 unsystematically selected patients with various neurological disorders, we
retrospectively investigated CSF results that had been raised during routine
diagnostic work-up from 41 consecutive neurological patients (predominantly
Guillain-Barré syndrome and autoimmune encephalitis) treated with
plasmapheresis or immunoadsorption in a tertiary care university hospital in
whom lumbar puncture (LP) was performed after a varying number of treatments
of therapeutic apheresis. Results Only when LP was performed 1 day after
therapeutic apheresis, spurious quantitative intrathecal immunoglobulin (Ig)
synthesis of at least one subclass (IgG, IgA and/or IgM) was found in 68.4 %
of the patients, irrespective of the number of treatments, in all age groups
and independent of other previous immunotherapies (e.g., steroids). This
phenomenon occurred only transiently and was almost always accompanied by an
elevation of the IgG index. In one patient, an elevated IgG index was noticed
even 2 days after plasmapheresis. Neither quantitative Ig synthesis, nor
elevated IgG index was observed when the LP was performed three or more days
after therapeutic apheresis. Conclusions Spurious quantitative intrathecal Ig
synthesis and increased IgG index are common findings shortly after
plasmapheresis or immunoadsorption due to altered serum immunoglobulin levels.
Knowledge of this phenomenon is needed for clinicians to prevent false
interpretations leading to unnecessary diagnostic and therapeutic procedures.
Misdiagnoses can be avoided by considering the characteristic CSF
constellation including absence of oligoclonal bands and the close temporal
relation to therapeutic apheresi
