Longitudinal Improvement in Respiratory Function Following Plasma Exchange in Patients with Severe Myasthenia Gravis.

backgroundThere are no data on the effect size and timing of plasma exchange (PLEX) in patients with myasthenic crisis (MC).

methodsWe retrospectively analyzed measurements of forced vital capacity (FVC) and negative inspiratory force (NIF) in the days before and after PLEX (administered every other day) in patients with MC admitted to a tertiary hospital over 4 years. For multiple measurements in one day, the average value was used. The day immediately before the first treatment with PLEX was considered baseline. Using time as a continuous or categorical variable in mixed-effects multiple linear regressions, we estimated predicted values for these tests.

resultsTwenty-two patients (mean age 67.3 years, 51.9% male patients) with 27 MC episodes and 508 measurements (234 FVC and 274 NIF; from 5 days before to 20 days after PLEX) were included. Presence of antibodies was detected in 70.4%. Intubation and mechanical ventilation occurred in 36.6% of patients. The mean number of PLEX was 5.1 (range 3-11). NIF values decreased before the first PLEX but increased after by on average 1 cm H

conclusionsSignificant increases in bedside respiratory measurements are observed as soon as the first PLEX day but with more variability on FVC than NIF, which may either reflect more FVC technique inconsistencies or more consistent effect of the treatment on NIF.