Long-term functional outcomes in immunoglobulin-treated multifocal motor neuropathy evaluated through the MMN-Rasch-built Overall Disability Scale

Abstract

Background Long-term functional outcomes are uncertain in immunoglobulin-treated multifocal motor neuropathy (MMN). Methods We retrospectively studied consecutive subjects with MMN from two neuromuscular centres in Southampton and Birmingham, UK. Initial and latest MMN-Rasch-built Overall Disability Scale (MMN-RODS) scores and latest immunoglobulin doses were collected. Latest dose alterations and resulting MMN-RODS changes were ascertained. Results We included 32 subjects with MMN (14 females and 18 males). Mean age was 60.0 years (SD: 11.7). Over a mean of 6.2 years, MMN-RODS scores improved in 29 out of 32 (90.6%) subjects and worsened in 3 out of 32 (9.4%) subjects. Mean latest centile MMN-RODS was improved compared to mean initial centile MMN-RODS (81.53 [SD: 14.14] vs. 63.47 [SD: 13.82]; p < 0.001). Mean latest immunoglobulin dose was 26.3 g/week (range: 4–70). There were no associations of the latest immunoglobulin dose with age/disease duration/weight/gender/comorbidities/initial disability/latest disability. There were no inter-centre differences in age/disease duration/weight/gender/comorbidities/initial disability/latest disability. The latest mean immunoglobulin dose was higher in Birmingham than in Southampton (33.9 g/week [SD: 17.1] vs. 18.8 g/week [SD: 8.0]; p = 0.004). Immunoglobulin dose dependency was observed in 16 out of 17 subjects whose last dose alteration was incremental, and in only 3 out of 15 subjects whose last dose alteration was decremental. Dose dependency was demonstrated in a greater proportion of subjects from Birmingham compared to Southampton (13/16 vs. 6/16; p = 0.03). Conclusions Function as ascertained by the MMN-RODS shows sustained improvement over > 6 years with individualised immunoglobulin dosing in most subjects with MMN. The large inter-centre/inter-individual dosing and dose dependency variations observed may suggest implications of patient- and physician-related factors, which require further study.