(P-TA-3) Characterization Of Spirometric Response To Therapeutic Plasma Exchange (TPE) And Factors Associated With Respiratory Distress In Myasthenia Gravis Patients

Background/Case Studies: Myasthenia gravis (MG) can lead to can lead to respiratory failure in 15-30% of patients. Although therapeutic plasma exchange (TPE) is frequently utilized to manage MG, consensus on the time course of response to TPE is lacking in literature. This observational, cohort study was designed to evaluate the spirometric response to sequential TPE procedures and identify factors associated with mechanical ventilatory support (MVS).

Study

Design/Methods: An observational, retrospective cohort study was designed. The electronic medical records were probed from 2009 to 2020. This study captured all pertinent demographic, medical history, Vital Capacity (VC) and Negative Inspiratory Force (NIF) in a series of MG patients managed with TPE at a single institution. Patients treated with a series of 5 TPE sessions who also had complete spirometric and clinical data were included in the study. Percent (%) of Maximum; Normal values for NIF (%NIFMax; %NIFNL) and VC (%VCMax; %VCNL) over time were assessed using linear regression with Response designated using an alpha < 0.1. Multivariate regression was used to identify factors independently associated with MVS.

Results/Findings: Of 41 patients in the study, improvement in mean %VCMax (56% to 91%) and %VCNL (43% to 70%) was observed in 26 patients (63%) after five TPE procedures while improvement in mean %NIFMax (59% to 93%) and %NIFNL (43% to 70%) was observed in 22 patients (54%).
Among responders, a linear (R2=0.97), time dependent increase in mean %VCMax and %VCNL values was observed after the third of five TPE procedures (Figure 1). %VCMax increased from 56% after TPE number 1 (i.e., at 16±8 hours), to 70% after TPE 3 (i.e., at 99±18 hours), and to 91% after TPE 5 (i.e., at 200±38 hours). A similar trend was noted with %NIFMax and MIFNL.
The following were independently associated with MVS (overall model r2 = 0.84) with listed (partial r values): male gender (0.77), higher doses of pyridostigmine (0.6), lower prednisone doses (-0.44), use of mycophenolate mofetil (0.51), pneumonia (0.75), absence of dysarthria (-0.45) or extremity weakness (-0.53) and both VC (-0.47) and NIF (0.69).

Conclusions: NIF and VC are important when assessing the risk for MVS and the requisite time for response with TPE, which was observed after the third of five TPE procedures.

Importance of research: TPE is frequently utilized to manage myasthenia gravis (MG) but characterization of the degree and time course of response to TPE using pulmonary function measurements is lacking in literature. This study characterizes spirometric responses to sequential TPE procedures, noting improvements in lung function after the third TPE session. In MG patients with impending respiratory failure, this can inform clinical decisions to initiate mechanical ventilatory support early, before TPE sessions.