Average hospital and intensive care unit (ICU) length of stay data were based on two studies. The first study compared the use of IVIG (400mg/kg/day for 5 days) vs. PLEX during 54 episodes of myasthenia gravis crisis at four major United States tertiary centers.11
IVIG was associated with an average ICU stay of 14 days (hospital stay of 17.7) while plasma exchange was associated with an average ICU stay of 17.4 days (hospital stay of 25.7). The second study evaluated patients from a nationwide inpatient sample database with ICD-9-CM codes for myasthenia gravis or myasthenia gravis crisis.12
This cross-sectional study found a median MGC hospital stay of 10 days with PLEX and 5 days with IVIG; although intensive care time after each therapy were not reported.
The estimated prevalence of side effects during PLEX or IVIG use for MGC was obtained from the best available prospective myasthenia treatment studies. Plasma exchange side effect prevalence was obtained from a prospective study evaluating the use of this therapy in 41 MG patients.13
The prevalence of IVIG side effects was based on a prospective study of 88 myasthenia gravis patients who received 1 gram/kg of IVIG on 2 consecutive days for myasthenia gravis exacerbation.14
Two additional side effects not reported in these studies were also given consideration given their potential to substantially increase the costs associated with PLEX or IVIG treatment. Although uncommon, the estimated incidence of stroke with IVIG use (0.6%)15
, and the potential incidence of death secondary to PLEX (0.02%)16
were included in the final cost assessments of these treatments.
Average costs for services and medicines (including daily professional fees, daily hospital rates, daily intensive care rates, costs for medicines, cost of IVIG, cost of albumin, cost of laboratory studies, cost of implementing PLEX, catheter costs, catheter placement costs, and catheter removal costs) were provided by the University of Rochester Billing Office and Lexi-comp. An average IVIG use of 400 mg/kg for five days, and an average exchange frequency of 5.5 was utilized.
All cost variables and their sources are provided in . Formulas utilized to calculate the total cost of each outcome arm are detailed in Supplemental Table 1
Using the above data, the average short term cost for utilizing plasma exchange for MGC was $101,140 per patient compared to IVIG which accrued an average cost per patient of $78,814. The TreeAge 4.0 cost analysis tree for these calculations is demonstrated in . The total cost for both IVIG and PLEX utilized the cost of all possible outcomes for each treatment and the likelihood that each of these outcomes occur. The average total difference in cost favored the IVIG arm with an estimated savings of $22,326 per patient.
Figure 1 Cost decision tree of IVIG vs. plasma exchange. Estimated total costs are provided for possible outcomes associated with each treatment arm. The average estimated cost for using each therapy ($101,140 for plasma exchange and $78,814 for IVIG) takes into (more ...)
For the IVIG therapy arm the greatest cost was for room and care in the intensive care unit (). At $21,581 the purchasing cost of IVIG comprised a significant portion of the total cost of implementing IVIG therapy. Although side effects with IVIG are reportedly common, the cost of treating these side effects was found to be low relative to other IVIG expenses.
Figure 2 Average itemized cost of treating a myasthenia gravis crisis patient with IVIG ($78,814 per patient) vs. Plasma Exchange ($101,140 per patient). For IVIG, the two greatest costs are the fees associated with patient time spent in an intensive care unit (more ...)
For plasma exchange, the greatest cost was for room and care in the intensive care unit (ICU) (). Because patients receiving PLEX spent more time in the ICU, these costs were comparatively higher than those in the IVIG arm. Exchange costs, non-ICU hospital care and room fees, professional fees, and the cost for albumin also produced a significant cost burden. Similarly to IVIG, costs secondary to side effects were relatively insignificant for this treatment arm.
Sensitivity analysis demonstrated that variations in several key variables significantly change the cost comparison of IVIG and PLEX for MGC. Specifically, the number of plasma exchanges required, the time a patient is required to be in the ICU, and IVIG dosing were found to be three of the most critical MGC treatment cost variables.
Historically, most MGC patients receive 4–6 exchanges; however, clinically this number can vary.11
A one-way sensitivity analysis of this specific variable demonstrated that the price of utilizing PLEX for MGC approaches (but does not equal) IVIG as the number of required exchanges becomes less ().
The comparative costs of IVIG vs. PLEX treatment of myasthenia gravis crisis based on the number of therapeutic plasma exchanges required.
Time spent in the ICU was also a critical variable in comparing the cost of treating MGC patients. A two-way sensitivity analysis of required ICU time for both PLEX and IVIG arms demonstrated that the comparative cost of MGC therapy is highly dependent on this variable (). In general, with equivalent or less ICU time, IVIG therapy was found to be the more cost saving therapy.
Figure 4 Two-way sensitivity analysis of PLEX vs. IVIG for myasthenia gravis based on ICU days associated with each therapy. PLEX is more cost effective for all points in blue whereas IVIG is more cost effective for all points in green. The associated ICU times (more ...)
Lastly, a sensitivity analysis on the mass of the myasthenia gravis patient was performed (). Dosing of IVIG is based on patient mass. This sensitivity analysis demonstrated that plasma exchange may become more economical than IVIG based on this variable alone, but only at patient masses over 162.8 kg. As most clinicians dose IVIG using ideal and not actual body weight, it is unlikely that IVIG dosing would frequently reach this level for MGC patients.
The comparative costs of IVIG vs. PLEX treatment of myasthenia gravis crisis based on the mass of the patient and subsequent IVIG dosing (total dose 2.0 g/kg).